Learn Me 5 Speed V6 F150

The F150 M5OD is supposedly stronger than the ranger version. If you're worried about heat put a full synthetic fluid in it and call it a day. Situations that would continuously put a lot of heat into it (e.g. trailer on the highway) are generally going to dictate 4th gear, where no power goes though the gears, so no significant heat is generated anyways.

I've never heard of them eating slave cylinders, I wonder if that might just stem from people trying to get more than one clutch out of them because they're expensive (though cheap compared to the labor of R&Ring the trans again), concentric slaves are not a part you should cheap out on. I have heard the slaves are hard to bleed though, like plenty of pro mechanics struggle with them.

I've had two friends personally need to do more than one slave in them over the course of a few years. One F150 one ranger. Granted that's only 2 people but definitely do not like the idea of having to pull the trans to do one.

My '89 never needed one but I also only had it a year or so.

The M5OD came in two types, the light duty R1 in the ranger and a heavier R2 in the F150. I had one live just fine behind a 300/6 in a previous gen F150. It was perfectly capable.

My M5oD has been flawless and needed nothing, I'm on the original clutch. I have beat on it pretty hard, but I do have mechanical empathy to a point. smoked the clutch real bad once trying to back up a hill fully loaded bed and trailer. Also the 4R70/75 auto they put behind these V6 trucks is way stronger than the manual.

My brother worked as a FORD technician and trainer for years. I have a Ranger with that transmission. He told me to never tow in the overdrive gear, its too weak and he saw a bunch of those transmissions go out because of it. You probably won't want to anyway due to low acceleration potential in overdrive/5th.

His assumption is that most gears are designed for infinite life at rated max output tq.

And that's basically true. Actual gear wear can pretty much never be considered normal at any mileage. It always goes back to fluid contamination or bearing play.

As far as heat, towing doesn't have a huge impact on that either. In an auto the most variable source of heat has to do with the torque converter being unlocked for long periods. In a manual there isn't really anything that generates a bunch of extra heat depending on load. To put it in perspective, in a lot of constant-mesh gearboxes friction-generated heat is such a big concern that they don't even put a bearing between the gears and the shaft in spite of the fact that 1st gear is probably spinning 10000 rpm faster than the shaft it sits on the whole time you're going down the highway at 70mph for all 350k miles it takes to wear out the bearings (not the gears and shafts!) in a manual transmission.

Also the 4R70/75 auto they put behind these V6 trucks is way stronger than the manual.

I think the 4r70w is a pretty good auto trans but it's definitely not more reliable than a manual that's always had fluid in it and not been driven incorrectly.

More load on the gear teeth during mesh will definitely cause more heat output. You can see the same in the rear diff. Hit it with an IR gun after a highway drive, then do that again after towing on the highway for a bit. I can guarantee it'll be a good bit hotter after towing (more average power through the diff, more frictional losses on the the gear teeth as they mesh, more heat).

Blaise wrote: As I suspected, the issue seems to be heat. We do helicopters here not trucks, but my understanding from my friend is that the above statement by curtis is correct. With the bed loaded or a trailer you're going to load it for LONGER, you can't load it more than the engine can output. His assumption is that most gears are designed for infinite life at rated max output tq. But it's likely a larger trans will handle the heat a whole lot better.

It was described to me like this:

Think of the load as a big box on the floor. The transmission is a piece of string tied to the box. The engine is someone pulling the string. If the person pulling the string is a toddler (4cyl) and the box is empty you won't have any worries. If you swap out the toddler for a body builder (V8), it won't affect the reliability of the string because the box moves long before the body builder can put enough force on it to break. If you keep the toddler but load the box full of books, the string still won't be affected because the toddler doesn't provide enough force to break it. The problem comes when you load the box AND have a body builder pull the string. (big engine, big load, small transmission).

Now, of course, a toddler pulling on a big box of books with a tiny string for a long time will weaken the string faster than an empty box, but not really in any catastrophic way.

In the case of the OP's V6 F150, the string is being pulled by the toddler, so it doesn't matter how many books are in the box. If he upgraded to a V8, he would need to upgrade the transmission to some 1/4" rope. In his case, he is more limited by how many books his toddler can pull. If the toddler can only pull 5 lbs and the string doesn't break until 8 lbs, you'll never break the string.

This is the engineering reasoning behind using a T56 behind the Viper V10. The Viper makes more torque than the T56 is technically rated for, but the engineering is safe-ish because of a traction limit.

Its also the same engineering that kept GM firm in putting 7.5/7.625" rear axles in F-body cars. The LS1 and T56 can make some serious shock loads, but with 245mm all-season rubber, they lost traction before they could eject the carrier through the cover.

I do agree, however about the heat. I wouldn't put 10k behind a V6/M5OD and go cross country, but I wouldn't hesitate (and actually did) use a V6/M5OD to tow 9k about 150 miles. The only concern I had was the big trailer with the short wheelbase truck, not the transmission.