Tag Ford 300 Inline Six

Published on November 4, 2025

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Part of the Bullnose Era Transmissions series.
Part of the Ford Truck Systems and Parts series.

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Show Transcript
If your bullnose still has that old four-speed cloer, you’ve probably thought about it. That five-speed swap — five real gears, smoother shifts, maybe even a little better mileage — is the promise of the Mazda M50. Sounds like the perfect upgrade right up until your 351 decides to eat it for lunch. Hi folks, Ed here. Welcome back to Mono’s Garage. Our subject is Ford’s most controversial 5-speed, the Mazda M50: the one that turned a lot of old-school truck guys into believers and just as many into skeptics. When they’re good, they shift clean and make your old truck feel almost civilized. But when they’re bad, you get whining, grinding, and maybe a little puddle under the tailshaft just to remind you who’s boss. I’m covering everything you need to know: the good, the bad, how to take care of one, and when you’re better off with a ZF5, especially if your truck has some muscle behind it. Picture the mid-’80s. Ford was trying to move away from brute-force manuals like the MP435 and the T18. Great boxes if you wanted to pull stumps, but they were heavy, loud, and about as refined as a tractor. The world was changing: fuel economy, emissions, and comfort started to matter. Ford wanted something that felt more like a modern pickup than a farm implement. Ford already had a solid working relationship with Mazda by then — they owned part of the company. Mazda was already supplying transmissions for smaller cars, and Ford knew they could build a gearbox that would shift smoothly. So they went to Mazda and said, ‘We need something that feels like your car boxes but can handle a truck motor.’ That’s how we ended up with the M50: a Mazda 5-speed with overdrive. A transmission born from Mazda’s smooth-shifting DNA but built tough enough, almost tough enough for Ford’s half-tons. It’s not something Mazda ever used in their own trucks. This was a Ford baby, raised in a Mazda factory. You’re going to hear a lot of alphabet soup with these — R1, R2, HD, and a few other oddballs — but really it’s just two families: the R1 for the little trucks and SUVs, and the R2 for full-size rigs like the F-150 and the Bronco. The R1 HD came later when Ford started hanging bigger engines on Rangers and Explorers. The R2 quietly got the same kinds of upgrades over the years: better bearings, stronger forks, little tweaks to make it live longer. There was even a version stuck in a Thunderbird Super Coupe, which is wild because it’s basically a truck transmission behind a blown V6. The first thing you’ll notice is the case. It’s all aluminum — bellhousing and all — cast as one piece. Saves weight, sure, but if you crack it you don’t just swap the bell; you’re shopping for a whole new transmission. Mazda didn’t mess around with separate parts on this thing. They also fully synchronized every forward gear and reverse, which was a big step up. No more double clutching to get into first. No more grinding into reverse because you didn’t let it stop spinning. It was a slick design for its time. The shifter connects straight into the top cover rails, so it’s got a tight, direct feel. None of that long-throw wooden-stick-in-a-bucket action like the MP435. You can tell Mazda tuned it to feel like a car, and when it’s working right it really does — the first time you drive one, you kind of forget it’s a truck transmission. All of that smoothness, though, came with a few compromises. There’s no oil pump inside; it’s all splash lube. That means the… Gears fling fluid around to keep everything happy. It works fine if you have the right fluid at the right level. We’ll get into that later, but that’s a big one. The clutch setup was another modern touch: hydraulic with a concentric slave bearing inside the bellhousing. Great when it’s working—smooth pedal, no adjustment needed. While Ford never published an official torque rating for the R2, in practice they live fine behind stock 300 and 302 engines. That means roughly 300 to 350 lb·ft of torque. Once you start making more power, like a healthy Windsor build, you run out of headroom pretty fast. It will take it for a while if you baby it, but you can’t dump the clutch at 4,000 rpm and expect it to smile. Dry weight on an R2 is about 115 lb depending on year. The R1s are lighter, more like 85 to 90 lb, but still no featherweight compared to a car transmission. The R2 is roughly 28 inches long overall, give or take, depending on the tailhousing. For comparison, the NP435 tips the scales closer to 130 to 140 lb, and the ZF5 lands in the 160 to 175 lb range, so you’re saving a solid chunk of weight, which was a big part of the design goal. Ratios vary a bit depending on year and application, but most R2 truck boxes fall in a similar range. You can find little differences between early and late units, and the Thunderbird SC version runs a bit shorter at 0.75 overdrive, but those numbers get you in the ballpark. In practice, first gear is a lot taller than the old 6.68 granny in an NP435—you won’t be crawling out of ditches with this thing. It’s built for driving, not digging. The overdrive makes a 3.55 or 3.73 rear gear feel perfect on the highway, the sweet spot for guys dailying their old trucks. Internally, it’s a five-speed, fully synchronized, constant-mesh box. The input shaft runs on tapered roller bearings front and rear with a countershaft that carries the rest of the geartrain. Mazda used brass or carbon-lined synchro rings depending on year: early ones were brass, later ones used the updated friction lining for smoother shifts. The gears are helical cut and quiet, and the countershaft sits in a pair of pressed-in races inside the aluminum case. The clutch splines are 1-1/16 in x 10, standard small-block Ford size, and the input shaft pilot is the same diameter as the NP435, so pilot bushings are easy to match. Output spline count depends on the unit: many 4×4 R2s are 31 spline, while two-wheel-drive versions are often 28 spline, so match the yoke to your specific transmission. Fluid capacity is about 3.8 quarts of automatic transmission fluid. Even though it’s a manual, they were designed for Mercon ATF, not gear oil. These transmissions are picky: gear oil is too thick for the splash action to lube correctly, and it will pool in the bottom while the transmission cooks. If you just bought a truck and don’t know what’s in it, drain and refill it—cheap insurance. When you look at what it replaced, the M50D was a step forward in the ways that mattered for the trucks of the time. It made old trucks feel new, made new trucks easier to live with, and gave Ford a shot at competing with the lighter, smoother rigs from GM and Dodge. It was the beginning of the modern era for Ford manuals, an era where a truck could still work hard, but. It didn’t have to sound like it was angry about it all the time. And now for the inevitable call to action: if you’re enjoying the video, hit like, subscribe, or better yet, check out patreon.com/bullnosegar. You’ll see some neat behind-the-scenes stuff and even more of me, which is definitely why you’re here, right? So we’ve talked about what the M50 is. Let’s talk about what it does when it decides to remind you it’s not bulletproof. Because for every guy who swears his M50 has been smooth and quiet for 200,000 miles, there’s another guy sitting on the side of the road with a dipstick full of glitter wondering what the hell just happened. The most famous failure, the one that’s practically a rite of passage, is the input bearing. That bearing sits at the front of the transmission right behind the input shaft, and it lives a hard life. Because it’s splash-lubed, the only oil that bearing gets is whatever gets flung up while the gears are spinning. On the highway that’s fine, but around town, especially with thick fluid or a low fill, it starves. It starts to whine, then it howls, then it eventually wipes itself out and takes the input gear with it. If you get a faint 45 to 60 mph whine under light load, that’s an early sign. If the pitch tracks road speed off throttle, start planning a teardown. The next most common issue is synchro wear, especially in third gear. Third is kind of the workhorse of the M50. It’s used a lot in city driving and it takes the brunt of any sloppy shifting or mismatched revs. Over time the synchro cones glaze, the rings lose bite, and you start getting that crunchy, notchy feel when you shift fast. If you have to baby it into third, that’s your sign. Sometimes fresh fluid helps, sometimes it’s just plain worn out. Shift forks are another weak link. They can crack at the base or wear the pads down so far the gear never fully engages. Then there’s the countershaft support bores. Over time the soft aluminum wears where the countershaft bearings sit. Once that happens the gears don’t mesh quite right, and you start hearing that high-pitched whine in second or third gear. Some rebuilders sleeve those bores or use oversized bearings to restore the fit, but if it’s really hogged out, the case is done. Let’s not forget the top cover leaks. These things love to seep around the lid and the shifter tower. The original gaskets were cork, and after a few heat cycles they shrink and weep. Most rebuilders just use RTV now and call it a day. It’s not catastrophic, just annoying. The good news is at least you’ll know when you have this issue because it’ll mark its territory on your driveway. Case cracking is less common, but it’s worth mentioning. The integral bell design means the case is doing double duty: it’s not just holding gears, it’s also part of the mounting structure. Over-torque the bell housing bolts or leave a dowel pin out and the whole thing can flex or crack around the flange. Usually it happens to people who rush a clutch job or bolt it up crooked. That’s a very expensive oops. And then there’s that funky internal slave cylinder. It’s technically part of the clutch system, but it’s inside the transmission. So when it leaks, you’re pulling the whole unit out to replace a $50 part. I don’t know who thought that was a good idea, but they very clearly never had to service one on a gravel driveway. And that’s really the story when it comes to the bad news. When they’re taken care of, they’re fine. But if you run them poorly, they will fail. The wrong fluid, slammed gears, or putting it behind a hot 351 asks it to do something it wasn’t born to do. If you’ve ever rebuilt a manual transmission before, the M50 isn’t that bad. But if you’ve never been inside one, it can humble you pretty fast. You don’t need a degree in rocket science, but you’ll want some mechanical sense, a clean workspace, and the right tools. Get a rebuild manual, or at least some photos before you start. The parts themselves aren’t hard to find. There are complete bearing and synchro kits on eBay, RockAuto, and some transmission suppliers that specialize in these. A typical rebuild kit runs about $150 to $250. Add seals, a new slave cylinder, and maybe a new shift fork or input bearing upgrade, and you’re still under $400 in parts. The biggest challenge for a rebuild here isn’t cost, it’s precision. Everything in this box runs on very tight tolerances. The manual calls for specific clearances, and those numbers actually matter. If that sounds intimidating, there’s no shame in taking it to a shop. A professional rebuild usually runs between $800 and $1,200 depending on how deep they go, how bad your core is, and where you live. You’ll get new bearings, synchros, seals, and usually a one-year warranty. That’s not bad for something that will last you years. If you want to keep one of these alive, keep a few things in mind. People treat them like an old iron four-speed and then wonder why it doesn’t act like one. This unit wants finesse, not violence. First rule: change the automatic transmission fluid every 30,000 to 50,000 miles. Second rule: be gentle when it’s cold. ATF is thick when cold, and these boxes don’t like to be rushed. Synchros need the fluid moving freely to grab cleanly. If it’s stiff or notchy in the first few blocks, that’s okay—don’t force it. Third, learn to shift with some feel. The shifter is short and precise, which is part of its charm. Hammering a two-to-three shift punishes the synchros. You’ll be amazed how much smoother and longer it will last when you stop pretending you’re running a quarter mile. If you’re towing or running it behind a torquey engine, keep an eye on heat. Long highway pulls on a hot day can cook the oil faster than you’d think. Some people drill a small port and plumb a cooler line, but for most, regular fluid changes are sufficient. And probably the biggest rule: be nice to it. No clutch dumps, no burnouts, no speed shifting at 4,000 rpm. It’s not a top loader or a Tremec. The gears are small, the case is aluminum, and the bearings rely on splash oil. That may sound delicate for a truck part, but that’s the trade-off you made when you left the NP435 behind. You gave up brute strength for drivability. That doesn’t mean it’s weak; it rewards the driver who pays attention. If you do that, it’s not unusual to see these go 200,000 miles or more before needing a full teardown. But if you neglect it, it’ll let you know in the loudest way possible. After all that, are you thinking about swapping one of these in? I was too until I did the math on how much torque I’ll get out of my old stoked Windsor. But if you’re here to learn whether that math works out for your truck, let’s set you straight, because yeah, the M50 will bolt up It fits a lot of engines, but that doesn’t mean it’ll survive them all. So let’s start with the easy one, the 3096. The M50 and the 3096 are a perfect marriage: smooth torque curve, low RPM, not a high-rev screamer. That engine and transmission were basically made for each other. Ford ran that combo from the factory for years, and it just works. You’ll wear out the clutch before you hear the transmission. If you’ve got a bullnose 300 and you want overdrive, this swap is a no-brainer. Next up, the 302. This is where things are still mostly safe, but the gray area starts creeping in. A stock or mild 302—headers, intake, maybe a small cam—the M50 will handle it fine as long as you don’t abuse it. You can even get away with towing light loads or running a little extra timing. But once you start building a serious 302—big cam, heads, high compression, or, God forbid, boost—that’s when the M50D starts sweating a little. In my case, the 351 wins here. This is where people get themselves in trouble. On paper, it bolts right up and it fits beautifully. In reality, a healthy 351 puts down way more torque than the M50D was ever really rated for. A bone-stock 351, especially a late-’80s smog motor, is probably fine. It’s right on the upper edge of what the transmission’s comfort zone is. But as soon as you wake it up—intake, cam, heads, maybe a stroker kit—you’re flirting with rapid, unscheduled disassembly. The truth is, if you’re running anything beyond a mild Windsor, you’re probably in ZF5 territory. The ZF was designed to handle torque in the 450 ft-lb range, sometimes more. It’s heavier, but it’s made for that kind of punishment. If your truck has a stock 300 or Windsor and you’re the kind of driver who rolls into the throttle and shifts cleanly, the M50 will make your truck feel like a new machine. But if you’ve got a heavy right foot or you treat every on-ramp like a drag strip, it’s probably the wrong transmission for you. And when you start talking transmissions to the Ford guys, you find out real quick everyone’s got a favorite. Half the crowd swears by the old MP435 because you just can’t break it. The other half worships the ZF5 like it’s holy scripture. And somewhere in the middle sits the M50—the good-enough five-speed that makes sense on paper and feels great behind the wheel but just can’t shake the shadow of those iron legends. If you’re trying to decide between them, let’s see what the competition looks like. We’ll start with the MP435 because every bullnose owner either has one or has fought with one. It’s a tank: cast-iron case, granny-low first gear you could practically climb a tree with, and enough mass to anchor a small ship. It’ll take anything you throw at it, but driving one every day is like doing manual labor. You’re rowing a gear stick the length of a pool cue through gates that feel like you’re stirring a bucket of rocks. Fantastic for crawling, horrible for commuting. The T18 and T19 are the same story. The old Borg-Warners are workhorses. Sure, they’re heavy and clunky and reliable as gravity, but they shift like they’re full of peanut butter. If you’ve ever double-clutched a T18 at a first-and-a-half stoplight, you know what I mean. Then there’s the mighty ZF5, the one everyone brings up when they say, “Yeah, but I want something strong.” They’re not wrong. The ZF5 is the heavyweight champ in this weight class: all aluminum like the M50D, but built like a bridge. Bigger gears, better… Oiling, a real pump inside, and torque ratings up in the 400s. It will take whatever your 351 or 460 can dish out. The trade-offs are weight, cost, and complexity. It’s a big transmission — about 40 pounds heavier — and it’s longer, so you’ll be dealing with driveshaft and crossmember work all over again. It also shifts a little more like a truck; it’s not bad, but it’s not nearly as slick as the M50. They can also be hard to find in the right configuration for your truck. If you want something modern and bulletproof, there’s always the TMIC route. TKO or TKX five-speeds will handle 600 lb-ft all day, but you’ll pay dearly for that privilege. Expect around three grand before the clutch, and you’ll still be fiddling with shifter replacement and crossmember alignment. Beautiful gearboxes, just not exactly budget-friendly. For most bull-nose guys, the M50 makes sense. It gives you overdrive, keeps the truck quiet, saves weight, and makes it feel ten years newer. It’s not a torque monster, but if you drive it like a grown-up, it will do what you want. If after all that you decide you want one of these middle-of-the-road, nice-shifting transmissions, let’s help you find one. The M50 R2 — that’s the big one from the F-150s and Broncos — uses the standard Ford small-block bell pattern. That’s the same bolt pattern as the 302, 351, and 300 inline-six. It will bolt right up to any of those; no adapter needed. That’s what makes it such a natural fit for bullnose guys, because your truck already runs one of those engines. The 300 and the Windsor family both share that pattern. For once, Ford kept building the R2 long after the bullnose years. In 1997, when the new F-150s came out, they reused the name but changed the bell pattern. The 4.2L V6 version got the S6/3.8L V6 pattern, and the 4.6L modular V8 version got its own modular-family bolt pattern. These won’t bolt to a 300, 302, or 351 without an adapter. And before you go hunting for an adapter, here’s the deal: nobody makes one. You would have to machine a custom adapter plate and deal with input shaft length, pilot engagement, and clutch spacing. The newer transmissions also run electronic sensors and have slightly different mount points. So even if you could get it to bolt up, it would still be a pain to get it to work right. The M50 R1 family is where things start branching out. The R1s came in Rangers and Explorers and used different bell patterns depending on the engine. The 2.3L four-cylinder version has its own pattern shared with nothing else. The 2.9L and 4.0L V6 versions share a Cologne V6 pattern totally different from the small-block Ford bolt circle. The 3.0L Vulcan V6 used another unique pattern shared with some Taurus and Tempo cars. The takeaway for full-size truck guys is that R1s come in every flavor of wrong. If you’re trying to hang one off a 302 or 351, the cases and bell are cast as one piece, so you can’t just swap a bellhousing like you could with an old top-loader or an NP — you have to swap the whole transmission. There is also one oddball version of the R2 that throws people off sometimes: the one used in the Thunderbird Super Coupe and the Cougar XR7 behind the supercharged 3.8L V6. It looks like an R2 on the outside but has a different bell pattern unique to that engine, plus a shorter tailhousing and a different shifter location. It’s a great gearbox for those cars. Totally useless for a truck unless you plan on doing some serious creative adapter-plate work. For swapping into a bullnose, you’re hunting for an R2 that came out of a 300 or a 302 truck. Even though they’ll bolt to a 351, they almost never came that way from the factory because the torque numbers are right on the line, and that pairing is so rare you’ll likely never see one. The easiest donor is an ’88 to ’96 F-150 or Bronco with a 300 or a 302. Beyond the bolt pattern, there are a few other things you’ll need to consider for this swap. The crossmember will probably need to move a few inches, and your driveshaft length might change depending on whether you’re coming from an MP435 or a T18. It’s nothing major, but it’s worth measuring before you start cutting. You’ll also need to move to hydraulic on the clutch if you’re not already. The M50 uses an internal concentric slave cylinder instead of an external fork. It’s a clean setup, but it means you’ll need a master cylinder, line, and the correct pedal assembly. If you’re handy, you could adapt the later F-150 hardware into your bullnose pretty easily. Some guys even use the whole clutch pedal box from the donor truck. Shifter placement is nearly perfect; in most bullnoses it lands right about where the factory four-speed shifter did. You might need to trim or move your boot just a little, but it’s not a hack job. The transmission mount pattern is a little different, so plan on fabricating a small adapter plate or modifying your crossmember. To summarize: if you’re looking for one in a yard, get the right donor. If it came out of a small-block or 300 truck, it’s basically made to live in your bullnose. If it came out of anything else, it’s probably not worth the trouble. If you find one in the wild, check that the bellhousing pattern matches your block before you buy it. In either case, spin the input shaft and listen—if it sounds like a box full of marbles, walk away. That’s your starting point for a bullnose swap that actually feels like an upgrade instead of a regret. The M50 isn’t a hero or a villain. It’s more like that buddy who will help you move furniture but draws the line at a piano. You have to respect it for what it is, not what you wish it was. It was Ford’s first real step toward trucks being something you could drive every day without feeling like you’d been in a fist fight. It wasn’t perfect, but it delivered something Ford desperately needed: a manual that made a truck feel modern, and one that served Ford well for the next decade. If you’re a bullnose guy seriously thinking about a swap, it’s one of the best ways to make your truck genuinely enjoyable to drive day to day. If you already own one, take care of it. Treat it like the precision piece of machinery it actually is. Do that and it’ll reward you with years of easy, quiet service. If you’re the type who can’t leave anything stock and you’re throwing serious torque around, that’s fine too—just know what the M50 is and what it isn’t. It’s not a race box. It’s not a heavy hauler. It’s a great, honest five-speed that gave old trucks a second life, and for that it deserves a little respect. That’s everything I know (or pretend to know) about the Mazda M50 five-speed. Do you have one you love or hate? Thinking about swapping one in? If so, drop a comment and let me know. If I change your mind, for or against, let me know. Know that, too. I really enjoy hearing about how this information might influence your decision. As always, if you have any questions, comments, concerns, gripes, or internet ramblings, stick them below. Thanks again so much for watching, and we’ll see you next time. If you want to dig deeper into the builds, the side projects, and the stuff that doesn’t always make it onto YouTube, or just want to get to know me a little better, come hang out on patreon.com/bullnosegar. It helps keep the lights on, keeps the beer fridge full, and funds the builds. I appreciate you being part of the garage. Shine Garage — she’s considered divine. Thanks again for watching; we’ll see you next time.

If your Bullnose still rows a four-speed, you’ve probably daydreamed about a five-speed that shifts clean, cruises quiet, and doesn’t feel like you’re stirring gravel. Enter the Mazda-built Ford M5OD. It turned a lot of old-school truck guys into believers and a fair few into skeptics.

In this deep dive, I break down what the M5OD is, why Ford used it, what actually fails, how to keep one alive, and when you should skip the drama and grab a ZF5. If you’re eyeing a swap behind a 300, 302, or 351W, this will save you time, money, and maybe a tow bill.

Ford × Mazda: What M5OD Really Is

Mid-’80s Ford wanted out of the tractor-transmission era (think NP435/T18) and into something that felt modern. They went to Mazda, already a partner and known for slick-shifting manuals, and asked for a car-like five-speed strong enough for half-ton trucks. The result was the M5OD: a Mazda-built five-speed with overdrive, purpose-built for Ford trucks. Mazda didn’t use it in their own trucks; this was Ford’s baby, raised in a Mazda factory.

There are two main families:

  • R1: Rangers/Explorers (light-duty), later with an “HD” variant
  • R2: Full-size trucks like F-150 and Bronco

Both evolved over time with better bearings, stronger shift forks, and small tweaks to help them live longer. There’s also an oddball: a version in the Thunderbird Super Coupe/Cougar XR7 behind the supercharged 3.8 V6. Looks like an R2, but the bell pattern, tail, and shifter location make it a car-only deal.

Design Highlights

There are a few choices that define the M5OD’s personality—both the good and the bad.

  • One-piece aluminum case and bell: Light and tidy, but if you crack it, you’re shopping for a whole transmission.
  • Full synchros (including reverse): No more double-clutching into first, and reverse doesn’t grind if you operate like a civilized human.
  • Direct top-rail shifter: Short, precise throws with a car-like feel. No “broomstick in a bucket.”
  • Splash lubrication: No internal pump. It relies on gears flinging ATF. This is fine—until you put in the wrong fluid or run it low.
  • Hydraulic, concentric slave: Smooth and self-adjusting. When it leaks, the trans has to come out to fix a cheap part. Ask me how much fun that is in a driveway.

Specs Snapshot (What Actually Matters)

  • Real-world torque range: Happy behind stock 300 and 302. A mild 351W is the ceiling. Hot Windsors push it past its comfort zone.
  • Weight: R2 around 115 lb dry. R1 closer to 85–90 lb. Lighter than NP435 and much lighter than ZF5.
  • Length: R2 is about 28 inches overall (varies slightly by tailhousing).
  • Ratios: First is tall compared to the NP435 granny; overdrive makes 3.55–3.73 gears nice on the highway. Thunderbird SC got a shorter OD (~0.75).
  • Guts: Helical gears, constant-mesh 5-speed, tapered roller bearings on the input, countershaft in pressed races. Early synchros were brass; later units got carbon-lined rings.
  • Splines: Input clutch splines are 1-1/16 x 10 (small-block Ford standard). Output is commonly 31-spline for 4×4 and 28-spline for many 2WD. Match your driveshaft yoke to the box you buy.
  • Fluid: About 3.8 quarts of Mercon ATF. Not gear oil. Gear oil is too thick for splash lube and will cook the transmission. If you don’t know what’s in there, drain and fill… cheap insurance.

Why Ford Used It

Compared to the iron legends it replaced, the M5OD made trucks feel newer, quieter, and less punishing to drive daily. It helped Ford keep up with the “modern manual” era… still a truck, but not mad about it all the time.

Common Failures (And What They Sound Like)

1) Input Bearing Oil Starvation

The celebrity failure. Splash lube plus thick fluid or a low fill means the front bearing doesn’t see enough oil around town. Early sign: a faint 45–60 mph whine under light load that tracks road speed off throttle. Ignore it and it’ll take the input gear with it.

2) Third-Gear Synchro Wear

Third does a lot of work in city driving. The synchro cone glazes and the ring loses bite. Result: notchy, crunchy shifts if you’re quick with the lever. Fresh fluid may help a little. If you’ve got to baby it into third, it’s wearing out.

3) Shift Fork Issues

Forks can crack at the base or wear pads so thin the gear doesn’t fully engage. That turns into pop-outs and more grinding.

4) Countershaft Bore Wear

The aluminum case can wear where the countershaft bearings sit. When that happens, gear mesh is off and you get a high-pitched whine (often in second or third). Some shops sleeve the bores or use oversized bearings. If it’s too wallowed out, the case is done.

5) Leaks and Seepage

Top cover and shifter tower love to weep. Original cork gaskets shrink; RTV fixes it. Annoying, not catastrophic. Just marks its spot on your driveway.

6) Case Cracking

Integral bell means the case is structural. Over-torqueing or misalignment can crack it around the flange. Leaving a dowel pin out or rushing a clutch job can get expensive fast.

7) Internal Slave Cylinder

When it leaks, the whole transmission comes out. It’s part of the clutch system, but it lives inside the bell. Whoever greenlit that never lay on gravel doing one.

Rebuild Reality: Tools, Cost, Precision

If you’ve rebuilt a manual before, an M5OD won’t scare you. If you haven’t, it can humble you. A clean bench, the right tools, and a manual or photo guide are mandatory. The box runs tight clearances and those specs matter.

  • Parts availability: Good. Complete bearing/synchro kits are plentiful.
  • Parts cost: ~$150–$250 for a kit. Add seals, a new slave, maybe a fork or an input bearing upgrade, and you’re still usually under $400 in parts.
  • Pro rebuild: Roughly $800–$1,200 depending on condition and region, often with a 1-year warranty.

How to Keep an M5OD Alive

  • Run the right fluid: Mercon ATF only. Change it every 30,000–50,000 miles.
  • Be nice when it’s cold: ATF thickens; synchros need fluid flow to work. Don’t force it in the first few blocks.
  • Shift with feel: The short shifter encourages hero moves. Every ham-fisted 2–3 punishes the synchros.
  • Avoid shock loads: No clutch dumps, burnouts, or speed-shifting at 4,000 rpm. Small gears, aluminum case, splash oil so act accordingly.
  • Watch heat on long pulls: Towing on hot days cooks oil faster. Some folks add a cooler with a drilled feed, but for most, timely fluid changes are enough.

Treat it like precision machinery and 200,000-mile service life isn’t unusual. Neglect it and it’ll sing you the song of its people right before it lets go.

Swap Sanity Check: 300, 302, 351W

300 Inline-Six

This is the easy win. Smooth torque curve, low RPM, and Ford ran this combo from the factory. If you’ve got a Bullnose 300 and want overdrive, this is as close to a no-brainer as swaps get.

302

Stock or mild? You’re fine, just don’t abuse it. Light towing and sensible driving won’t scare an R2. Once you go big cam, big heads, high compression, or (bless your heart) boost, you’re into “this gets expensive” territory.

351 Windsor

It bolts up and fits great on paper. Reality check: a healthy 351 makes torque the M5OD wasn’t built to digest long-term. A smog-era stocker is on the edge of acceptable. Wake it up with intake/cam/heads, or a stroker, and you’re flirting with rapid, unscheduled disassembly.

If your build goes past “mild Windsor,” you’re in ZF5 territory. The ZF5 was designed for torque in the 400s and has real oiling with a pump. Heavier and longer, yes, but it’s built for that punishment.

Alternatives: What You’re Comparing Against

  • NP435 / T18 / T19: Iron workhorses with granny-low first. Nearly unbreakable, but heavy and clunky. Great for crawling, awful for commuting.
  • ZF5: All aluminum but beefy. Bigger gears, internal pump, torque ratings in the 400s. Heavier/longer (driveshaft and crossmember work required) and a bit more “truck” in shift feel, but the right answer for real torque.
  • Tremec TKO/TKX: Modern aftermarket option that’ll take serious torque, but pricey and you’ll still be sorting shifter placement and mounts. Awesome gearboxes; not budget-friendly.

Finding the Right M5OD-R2 (And Avoiding the Wrong Ones)

You want the R2 from an F-150 or Bronco with a 300 or 302. That lands you in the 1988–1996 donor window with the small-block Ford pattern that bolts to 300/302/351W.

In 1997, Ford reused the name but changed the pattern:

  • 4.2L V6: Shares the 3.8/Essex V6 pattern
  • 4.6L modular V8: Modular-family pattern

Those won’t bolt to a 300/302/351W without an adapter and nobody sells an off-the-shelf adapter. Even if you custom-machine one, you’ll have to sort input length, pilot engagement, clutch spacing, sensors, and mount points. It’s a headache you don’t need.

About the R1 Family

R1s came in Rangers/Explorers with multiple bell patterns (2.3 four, 2.9/4.0 Cologne V6, 3.0 Vulcan V6). The bell is cast into the case, so you can’t swap bells. For full-size trucks with 300/302/351W, R1s are basically every flavor of wrong.

The Thunderbird SC Oddball

Looks like an R2, but it’s unique to the supercharged 3.8 V6. Different bell, shorter tail, different shifter location. Great for that car, useless for a truck unless you love fabricating adapters.

Yard Tips & Fitment Notes

  • Check the bell pattern: Make sure it matches your block before you hand over cash.
  • Spin the input shaft: If it sounds like a box of marbles, walk away.
  • Output splines: Know if you’ve got 28- or 31-spline and match the yoke.
  • Crossmember: Plan to move it a few inches. The mount pattern differs; a small adapter plate or minor fab solves it.
  • Driveshaft length: May change depending on what you’re coming from (NP435, T18, etc.). Measure before you cut.
  • Hydraulic clutch conversion: You’ll need a master, line, and the right pedal setup. Many folks adapt later F-150 hardware; some swap the whole pedal box.
  • Shifter location: Lands close to where the factory four-speed shifter was. You might massage the boot a bit—nothing hacky.

So… Is the M5OD the Right Move?

The M5OD isn’t a hero or a villain. It’s the buddy who’ll help you move a couch but draws the line at a piano. Respect what it is: light, smooth, honest. It makes an old truck feel ten years newer. Abuse it or throw big torque at it and it’ll remind you it’s splash-lubed aluminum with smallish gears.

If you’re driving a stock 300 or a mild 302 and you shift with some finesse, the M5OD is a great upgrade. If your right foot is heavy or your Windsor is spicy, save yourself the rebuild and start with a ZF5.

Wrap-Up

I broke down the history, what fails and why, how to rebuild or maintain one, donor years that actually fit, and where the M5OD makes sense (and where it doesn’t). If you’re swapping into a Bullnose, get the right R2 and set it up properly and you’ll actually feel like your truck wants to commute.

Got M5OD war stories or a swap plan? Drop them in the comments. Want the full rundown in motion? Check out the video above and let me know what you think.


Bullnose Garage at YouTube

If you want more specific information on Bullnose Ford Trucks, check out my YouTube Channel!

For more information on Bullnose Fords, you can check out the BullnoseFord SubReddit or Gary’s Garagemahal. Both are excellent resources.

As an Amazon Associate, I earn from qualifying purchases. If you see an Amazon link on my site, purchasing the item from Amazon using that link helps out the Channel.
300 Six Fuel Pump Replacement

Published on August 11, 2024

Click to play the video inline  or  see it on YouTube

Part of the The Bullnose F-150 series.
Part of the Ford Truck Systems and Parts series.

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Show Transcript

Howdy folks, Ed here. Welcome back to Bullnose Garage for the first time, and man, it’s been almost two years. Uh, life, pandemic, all kinds of stuff just got in the way of me working on this truck. And I’ve gotten several comments on many of my videos asking where I am and what’s going on, and people even actually worried about me, and I appreciate that. I really do. Uh, everything’s fine.

But today, the reason that I’m out here right now is because something broke on the Bullnose, and I need to fix it. And the last thing that I want to do is fix something on that truck without bringing you guys along with me. So what broke is this. It’s a mechanical fuel pump. So I try to start my truck every couple of weeks at the very least just to get it running and make sure that it’s okay, make sure the battery stays charged, all that fun stuff. Then about once a month or so, I’ll go out and, uh, actually stretch its legs, run it for, uh, you know, 10, 15 miles, something like that, and then bring it back and make sure that it’s running all right.

And this last time I went out to start it, it was kind of hard to start. I had to give it a whole lot of gas, and it cranked and cranked and cranked and wouldn’t catch. And then eventually it did catch and then die, and then it caught and then died. And then I gave it even more gas, and it caught and then it ran, but it sounded kind of strange, and I started smelling a little bit of gas. And so I turned it off and opened up the, uh, the hood back there and looked underneath, and there’s a big puddle of something, and it wasn’t oil, and it smelled like gas. So I’m guessing it was gas.

And sure enough, I turned the truck on and, uh, went back around to the front, and you could see it was running, but you could see, uh, where the fuel pump was just draining fuel, um, out onto the driveway here. And I don’t know if you’ll be able to see this or not, but these mechanical fuel pumps are designed with a little weep hole right here. So they’ve got a diaphragm inside of here, and then this, this, uh, right here rides on top of a cam inside the engine. And, uh, if that diaphragm goes out, it leaks out of this hole as an indicator to what, you know, that there’s something wrong and you got to replace it. And there’s no fix in the diaphragm. You can’t get in here, and there’s no serviceable parts. This thing is like a one-piece unit, and it’s like 30 bucks, so it’s not worth even trying to fix anyway, even if you could.

Um, so just go out and grab yourself a new one if you’ve got that problem. And these are actually, uh, pretty easy to change. You just get in there, takes a, uh, I think it’s like a 12 millimeter or a half-inch driver with a ratchet, and, uh, you got to get yourself the fuel pump itself. Like I said, it’s about 30 bucks. I got myself a Felpro gasket, like two bucks, and, uh, I didn’t have any of this, so I went out and grabbed some Permatex Orange. Um, that’s what’s good around fuel, uh, just to go around the gasket there. Now, there shouldn’t be any fuel touching that gasket. It’s in between the block and the fuel pump itself. There’s some oil in there, but there shouldn’t be any gas. But anyway, it’s around the fuel line, so in case something were to break or bust, I don’t want that getting out of the gasket material and giving me problems, so that’s why I’m using that.

So let’s get to it. All right, so that right there is the fuel pump. The, uh, line on the bottom of your screen, let me move this up a little bit so you can see, that’s going to the fuel tank, and the one on the top in the back there is going up to the carburetor. And you can see that, uh, there’s a bracket right there, and, uh, that bracket holds the ignition coil connector. Uh, so we’re going to have to remove that bracket as well. Now, not all vehicles have that, but mine happens to. Um, let’s see, and again, this is on a 3006. Uh, your mileage may vary, but, uh, on my ’85 36, this is how everything’s set up.

Now, a lot of these fuel pumps actually have the can facing down. In my case, it faces up. That’s just the way that it is. So I’m not sure if you can see it from this angle here. There’s a couple of bolts that hold that on, so it’s a fairly easy replacement, and we’re going to start by taking off the lines. So we’re going to start with this fuel line from the tank. Um, now, because my truck is outside, I’ve already leaked a bunch of fuel on the ground. I don’t really care that much, but if you’re going to be inside of your garage or in a place where the floor kind of matters, you want to make sure to put something under the truck because you might get some fuel leaking out of here when you take it off. And you just, uh, loosen up this hose clamp here and wiggle it off. Takes a little bit of force, especially if it’s been on there for a while. You just take it right off, and you want to cap this with something. I’m just using a driver extension and then kind of tuck that out of the way.

Now for the other one, we need to get a wrench in there and loosen that up. Now for the line going to the carburetor, I’m going to use a 5/8 flare nut wrench, and I’m going to use that because I don’t want to have to round this nut off and replace this line. So, um, whenever you’re working on, like, brake lines or lines like this, it’s always a good idea to use a flare nut wrench, um, because they have a more positive grip and you’re less likely to round things off. It makes them harder to get on. They’re a little bit, takes a little bit longer to do, but it’s just a little bit of insurance.

All right, that took a while, but we are on. Okay, I’m trying to get you guys a pretty good angle. Um, it’s a little hard to get down in here and see what I’m doing, but the next step is to actually unmount it from the block. And if you can see there, a couple of bolts there, they are half-inch, and so I would use my half-inch ratchet to take them off. Oh, and I was wrong. They’re not bolts, they’re nuts. That’s what happens if you’re not a mechanic. You think you know something, and then you’re not. Because, um, I have this, uh, um, ignition coil bracket behind there, uh, and it’s down by where the gasket is, I’m going to have to take that off so that I can get to the existing gasket and make sure that I get all that gasket material out of there. So this is a 9/16, and it’s right up here, and now I can move this out of the way and actually get to the pump.

So here’s something that I actually didn’t know about and expect. Um, the first bolts that I took, or the first nuts, excuse me, that I took off of the bottom where the fuel pump is at actually held this bracket on. So the actual fuel pump mounting, uh, nuts are still on there. So now I have to remove those, and they are also a half-inch. And up she comes. Now that I’ve got the fuel pump out of there, you can see inside the cam that’s down there that the fuel pump, um, arm rides on. You can also see all the, the gasket material that’s left on there. We want to make sure we get all that gasket material off so we have a nice clean mating surface with the block again for the new pump.

I want to start by using a, uh, a nylon brush just to kind of peel away the gasket material that’s there. You don’t want to be too harsh because you don’t want to, so there’s not actually even a gasket there. It looks like there’s just some gasket material that someone had put on before, and I have an actual gasket that I’m going to use. But, uh, make sure this is nice and clean. You don’t want to be too harsh and rough up too much, but you do have to make sure that it’s nice and clean. And now finally, get this as clean as, uh, I can. Oops, out of the way. I’m going to use this brass bristle brush. Brass bristle brush, um, it’s a little rougher than nylon but not as rough as steel. And this is just, uh, if I had a scratch pad, I’d probably use a scratch pad, but I don’t have one. Um, you could probably use steel wool, but that may be a little bit harsh for me. So that’s just to make sure that I got any remaining gasket material or any other kind of contaminants, uh, definitely off of there. And then I’m going to, uh, take some isopropyl alcohol and dilute it just a little bit. It’s not quite so strong, and give it a good final rub down with a shop rag just to make sure I don’t have anything going around there. Then we will let that dry and take a look at the old pump.

All right, so there’s our old pump, obviously, and our new one. And, uh, you, I mean, you can’t visually look at this and tell that it’s bad. Um, yeah, there’s not really any kind of diagnostics that you can do, um, except run fuel through it and watch it pour out of the weep hole. Um, that’s about it. But, uh, as you can see, they’re not exactly the same, but, uh, they’re definitely going to fit. So now the next job is just to install the new one. Just a quick note here, um, there can be some difficulty with installing these because of the position of the cam. Um, sometimes you’ll have to actually turn the engine. Um, you have to get on the crankshaft pulley with a ratchet or something or a breaker bar and actually turn the engine a little bit to get that cam into the right position to put this in. You can muscle this in without doing that. It’s kind of up to you how you want to do it. This one came out really, really easy, so I’m hoping that my engine is in the correct position to make it pretty easy to install this one. Uh, we’re going to find out.

So my first job here is going to be getting this gasket, um, onto here. The easiest way to do that is to take some of your gasket maker and just run a little bit seal area here, okay? And then you can put your gasket on, and what that’s going to do is that’s actually going to sort of lock the gasket to this part, and that way you’re not fighting with the gasket to stay on, um, while you’re getting it actually on the engine itself. And then while you’re out here, you actually do the same thing the other side, just a real light thin coat here. You don’t want too much. You don’t want it really oozing out, just enough to go around all the surface areas so that, uh, it mates real good and it fills in any micro gaps or anything between this gasket and the block itself. So let’s get to it.

All right, here we go. This is kind of hard with the camera here, but this is a little tight, but you just keep at it, and it’ll get in there. It’s a little hard to work with. I don’t really have a lot of space here for my fingers. There we go. Getting these in is kind of the hardest part, and I can see my gasket starting to get tacky, so I want to make sure that I get this tightened up really quickly. Sorry if you’re wobbling around. Sometimes this stuff is hard to do with the camera in the way. There we go. Now we want to slide our bracket back on. Should be fairly simple, just like that. I’ll get this thing tightened up and be right back with you.

All right, so it’s now installed. The only thing that remains is to put the, uh, the hoses back on. Now this is going to be tricky. You want to make sure that you’re not going to cross-thread that as it goes in. There we go. Now, like I said, wh off my sunglasses. Now, like I said, you want to be careful that you don’t cross-thread this nut right here. Um, it took me a little bit to get it in the right position. You may have to actually bend your line just a little bit to, uh, to get it to line up. You’ll know when you get it right ’cause it’ll start going on, uh, fairly easy. If it’s real, real hard to get on there, then you’re probably cross-threading it, and you don’t want to do that because then you have to replace this nut, flare nut right there, and, uh, that means replacing the whole line. So you want to make sure you’re careful.

And the last thing is putting your fuel line back on, and you just shove it on there, make sure it goes on all the way, and you can, uh, tighten up your hose clamp. All right, now we should be good to go. Now when you go to start this, it’ll probably take a long time because that have to pre, so, uh, be patient, and we’ll see how long it takes.

All right, here we go, and success! There is no fuel leaking out of my new fuel pump. Keep an eye on it just when you first, uh, get it started up. Make sure all your connections are dry, and you put your finger on it, you can actually feel the vibration of that pump lever in there moving up and down on the cam. At this point, I think we’re good to go.

All right, guys, well, there you go. Pretty simple job, a little bit dirty, but what is it? And, uh, pretty cheap too. Actually, it’s about, uh, I think, uh, 30, 40 bucks for all the parts that you need to do it. Um, it’s about an hour’s worth of work for me, and that includes filming. So for, uh, somebody who doesn’t have to worry about dealing with the camera and getting the right angles and going through all that stuff, it’s probably really a 20, 30-minute job at the worst. If you’ve never done it before, um, it’s a little fiddly getting in there sometimes, get those bolts out, and you got to be careful with that fuel line that you don’t, uh, cross-thread that flare nut or round it off or anything like that. But I mean, as long as you’re careful, you’re not going to worry about, uh, the truck runs like a top once again. It’s nice to have the old inline six running great again. Um, sounds as good as it did before, or actually probably better now with the new fuel pump. Uh, took it around the block a couple times, no issues at all, no leaks, no nothing. So it’s very nice to have that thing back on the road again.

As always, if you have any questions, comments, concerns, gripes, internet ramblings, stick them below. Thanks again for watching, guys, and we will see you next time.

Hey folks, Ed here from Bullnose Garage. It’s been a while since I cracked open the hood of the old ’85 Ford F150 on camera, but today we’re diving right back into it. Seems like the universe conspired to keep me away with all kinds of life stuff, but the Bullnose decided it had enough of sitting idle and developed a bit of a fuel problem.

So, in this video, I tackled something that every classic Ford truck owner will likely face at some point—replacing the mechanical fuel pump on a Ford 300 Inline Six. Let’s break down the process, shall we?

Diagnosing the Fuel Pump Issue

It all started with the truck being a bit stubborn to start. You know the drill—crank, crank, crank, and still no joy. When it finally fired up, the engine ran rough and there was a whiff of gasoline in the air. Cue the dread.

As it turns out, the mechanical fuel pump was leaking gas. These pumps have a nifty little feature—a weep hole—that lets you know when the diaphragm inside has called it quits. When fuel starts dribbling out of this hole, it’s your cue to swap the pump.

Tools and Parts Needed

You’ll need a few tools to get this job done: a 1/2-inch ratchet, a 9/16-inch wrench, and a 5/8 flare nut wrench. For parts, grab a new mechanical fuel pump, a Fel-Pro gasket, and some Permatex Orange Gasket Maker. All in, it’s about 30 to 40 bucks.

Removing the Old Fuel Pump

First things first, disconnect the fuel lines. The line from the fuel tank can be a bit messy—so, toss a pan under there unless you want your driveway smelling like a gas station.

The line to the carburetor is a bit trickier. Use that flare nut wrench to avoid rounding off the nut. Trust me, the last thing you want to do is replace that whole line.

Cleaning the Mating Surface

Once the old pump is off, you’ll see the cam inside the engine where the pump’s arm rides. Clean off any old gasket material from the engine block. I used a nylon brush to keep it gentle, but threw in a brass bristle brush for the stubborn bits.

Installing the New Fuel Pump

Slap a bit of gasket maker on both sides of your new gasket and position it on the pump. This helps keep the gasket in place while you maneuver the pump into position.

This can be a bit fiddly, especially if the cam isn’t in the perfect spot. Sometimes you have to turn the engine a smidge to line things up. Once it’s seated, bolt it in, reattach the lines, and make sure everything’s snug.

Testing the Installation

Once everything’s back in place, fire up the engine. It might take a bit for the fuel to get moving, but once it does, check for leaks. If all’s dry and running smooth, you’ve nailed it.

Conclusion

And there you have it—a fairly straightforward job that won’t break the bank or your back. If your Bullnose starts acting up with similar symptoms, now you know what to do.

Got questions, or just want to share your own tales of wrenching on a Bullnose Ford? Drop them in the comments below. Thanks for sticking with me through the hiatus, and I’ll catch you in the next video!


Bullnose Garage at YouTube

If you want more specific information on Bullnose Ford Trucks, check out my YouTube Channel!

For more information on Bullnose Fords, you can check out the BullnoseFord SubReddit or Gary’s Garagemahal. Both are excellent resources.

As an Amazon Associate, I earn from qualifying purchases. If you see an Amazon link on my site, purchasing the item from Amazon using that link helps out the Channel.