M5R2 (M5OD-R2) Rebuild Deep Dive

[97Sandbox]

It's that time! I have enough concerns about the 4x4 M5R2 that I swapped into my Mounty that it's time to rebuild. I also have a 2wd version that's going into my Sport and it has a sloppy input shaft too so I'll rebuild that as well, though I don't believe the two transmissions have different internal components except for the output shaft.

A bit of background: both transmissions are from 10th generation F150s that had 4.2 V6 engines. The 4x4 came from a '97 with about 120k on it -- I pulled it myself. The 2wd was already pulled when I bought it, but supposedly it came from a '98 with just under 90k on it. The input shaft feels loose on both of them and the 4x4 unit has leaked for as long as it was in my Mounty. Looks like one of the leaks came from fluid sloshing out of the shift stub boot:

Dry as a desert under the notorious rear plugs though.

Rear main looks dry too:

There was definitely fluid sleeping between the main case and the tail housing though. I think that's just a bead of RTV.

 

[97Sandbox]

How do these shift forks look?

1-2 in 4x4:

3-4 in 4x4:

1-2 in 2wd:

3-4 in 2wd:

I think these are all okay, but need to do some F150 forum research unless there's a transmission expert who can set the record straight.

The gears in both transmissions looks good -- no mangled teeth and no glittery oil.


I need to tear these down further to figure out which 5th gears I have. There were two different tooth counts and I believe the change happened around '97.

It makes a difference for which rebuild kit you get, which is why I haven't ordered any yet.

 

[97Sandbox]

Okay, I think I get what I'm looking for on the shift forks now. These pictures are probably more useful. The lower mileage, 2wd forks look pretty good to me:

There are wear marks, but not really any "step."

However, the 4x4 forks have more noticeable wear and a decent step on the 1-2 fork:

Anyone have a suggestion for what's considered allowable wear on these? Thanks!

 

[97Sandbox]

Moving along on the 4x4 trans (I don't have room on my table to tear both down simultaneously). Tail housing off:

Is it still called the tail housing on a 4x4? Intermediate housing would probably make more sense. The rear output shaft bearings and rear counter shaft bearings feel good, nothing like the play in the front input shaft bearing.

Looks like the magnetic drain plug has done its job these past 1500ish miles:

The fluid that came out is dark, but not glittery.

I also pulled the slave off and the plate that sits behind it. Next comes the input shaft.

 

[97Sandbox]

The case is empty now.

I pretty much followed this video, but had a much harder time getting the input shaft separated from the rest of the main shaft than the guy in the video.

I'm somewhat surprised that I'm not seeing nearly the wear I expected. None of the gears or synchros look chewed up in the way I expected. The only chipped up piece I see is this guy from the back of the countershaft:

I'm guessing that's why I had such a hard time getting into reverse? Or possibly that's the result of grinding my way into reverse.

I'm also puzzled that my input shaft bearing and race do not show any signs of galling or heat discoloration:

Could it be that the play in the input shaft was acceptable? Or, since this is a tapered bearing, is an additional shim necessary between the race and the cover plate?

I'm hoping someone who knows what they're looking at better than me can shed some light on things. Thanks in advance!

I did confirm this '97 transmission has a 33-tooth reverse gear, but I'm going to hold off on buying a rebuild kit because I'm not sure I even need replacement synchro rings.

 

[410Fortune]

*****in work! Following along here

These are tough transmissions

There is no slop in the input shaft once it’s jammed through the clutch and into the pilot bearing

 

[97Sandbox]

I was reading more on various F150 forums and came to the conclusion that my input shaft bearing may be okay after all. Supposedly some radial play (up/down right/left) in neutral is very normal and you're supposed to evaluate clearance while in gear. Wish I'd done that before all the disassembly! I believe axial play is the only one that can be adjusted via shims.

I'll check my 2wd transmission before I blow it apart, it has a similar amount of play to what this 4x4 had. I had noticed the input bearing race had some play in the 4x4 case as well, but now I read that's normal too.

Regardless, my 4x4 transmission clearly needs the reverse gear and 5th/reverse slider replaced. I think at least the 1-2 shift fork needs to be replaced too.

Transmission experts: please take a look at the pictures and let me know if you see anything else that needs replaced. I can always get more pictures. Thanks!

The way this is going, I'm thinking leave the bearings and synchro rings, replace the reverse gear and slider, replace the 1-2 shift fork, and put everything back together with new seals. But I'll wait for some input.

 

[97Sandbox]

I messed with my 2wd transmission and there's still plenty of input shaft radial play when it's in gear, so I'm going to be getting bearings for both transmissions after all.

One thing I noticed online is that the caged needle bearings for individual gears are not included in the rebuild kit. Do those typically not need to be replaced?

 

[97Sandbox]

After I did all that disassembly yesterday, I realized you don't actually need to take the reverse gear out to count the teeth. I pulled the tail housing off my 2wd and there's easy access:

At a glance, this transmission looks cleaner and less worn than my 4x4, which makes sense if it truly has only 75% of the miles.

It's amazing to see how much more corroded the 2wd is outside though. I bought it when I lived in Milwaukee, so it likely came from a real rust bucket. The 4x4 came from a t-boned work truck here in Nebraska, where much less salting goes on, so it's cleaner outside.

 

[97Sandbox]

I dug up a Ford service manual last night which has good procedures for checking input and counter shaft clearances after/during reassembly. It also has all the torque specs and helpful diagrams.

I've been trying to figure out how to visually evaluate gears and synchros for wear, aside from the obvious stuff like my chipped up reverse gear and slider. This video was really helpful.

I also read about checking the input shaft by test fitting a new pilot bearing on the tip. Both of my input shafts still have good splines, but the pilot bearing feels a bit loose on each. Admittedly, I don't know what the clearance should be though, it'd make sense to me for that one to be on the looser side.

I'm trying really hard to call things by their proper name. After digging, I've realized the gears from front to rear are 4th, 3rd, 2nd, 1st, 5th, and reverse. It's easy to get mixed up when you're new at this!

 

[97Sandbox]

On my 4x4 transmission, I found my front input shaft bearing feels good, but my front countershaft bearing binds. Both rear bearings feel good, as does the pilot bearing between the main and input shafts. However, I think I'll go ahead and replace all the shaft bearings. My needle bearings all feel good, and from what I've read, those seldom wear at a rate anywhere near the others.

The input shaft gear teeth show wear though, so I think it needs replaced regardless of bearing surface condition.

Most of the synchro rings look okay, but there are a couple that look worn:

I think I'll just get the full kit with bearings and synchros as well as an input shaft, shim kit, and new shifter cover/gasket. I still need to measure shift fork/slider clearance to decide whether the forks are too worn.

 

[97Sandbox]

On my 2wd transmission, the input shaft 4th gear teeth look a bit worn too:

Not as bad as the 4x4, but you can see what was a crisp edge is turning into more of a ramp.

The synchro rings in this one look okay to me though.

And the reverse gear on this one looks fine to me too:

So for the 2wd, I'm thinking I'll get an input shaft and shim kit, the rebuild kit with bearings and seals (but no synchro rings), and I'll put a new shifter cover/gasket on this one too.

I'll measure the shifter fork clearances too, but these ones don't seem near as worn as the 4x4.

 

[410Fortune]

How much is the rebuild kit?

Nice work man!!

 

[97Sandbox]

Just seals: $22
Seals and bearings: $243
Seals, bearings, synchro rings: $325

The needle bearing set is $50 more.

 

[97Sandbox]

The more I'm looking at things, the more I'm thinking my brass synchro rings may not actually be that worn. Right now I'm tempted to buy the kit with seals and bearings only for my 4x4. The new reverse gear/slider comes with a reverse synchro ring.

I have noticed that there appears to be more wear on the 4th gear side of the 3-4 sliders on both transmissions:

This makes sense since that's what engages the teeth for 4th on the input shaft, which also look worn.

I'm starting to second guess myself on what's really worth replacing on each transmission. Is it really worth doing all the bearings, or just the ones that feel rough? Should I leave the synchro rings that look okay, or replace them all while I'm in here? Is the input shaft wear actually concerning? I never really had an issue getting into 4th compared to some of the other gears.

If anyone has knowledge of these Mazda units and can provide some recommendations, I'd sure appreciate it. Thanks!

 

[97Sandbox]

Oh, I should also add that I checked my shift fork clearances and all were in spec except the 1-2 fork on the 4x4 (which does not surprise me). I'll definitely replace that one.

 

[410Fortune]

$325 for the whole kit and you are already in there… I would replace all wear parts

Having the new synchros in your hand will help determine how much wear is on the old ones

 

[97Sandbox]

My dilemma is that the synchro sliders look more worn than the synchro rings and sliders aren't included in the rebuild kit. The 5th/reverse slider 100% needs replaced in my 4x4. The 3/4 looks worn on the 4 side, but the site that sells most of these kits and parts doesn't sell a 3/4 slider for '96+ M5R2. RockAuto has the 3/4 slider for $82, but that's enough to make me ask twice whether I really need it. I don't see the 1/2 slider available on the sites I trust.

Input shafts are $113, shim kits are $42, gears are $60-100 each, needle bearings $50. What I'm getting at is if you take the "just replace it while you're in there" attitude, you start to approach the cost of a full remanufactured transmission ($1500-1800) pretty quick with just the sum of the parts prices.

 

[97Sandbox]

I cleaned the case, tail housing, and front cover of the 4x4 this afternoon. Took some work to get all the sandy ATF gunk off.

I've been looking at the parts on my bench more and more and I've determined that all the gears have pretty noticeable wear. I don't think that's any surprise for 4th gear (input shaft), but it seems uncommon for most of the others. I was already pretty much set on replacing 5th and definitely reverse, but it seems 3rd is the only one of the other three that's readily available. I can only find 2nd listed as out of stock and I can't find 1st at all.

Since all the gears except 4th/input shaft look good on my 2wd transmission, I'm debating about finding another low-to-moderate mileage 2wd unit just so I can steal the gears off the main shaft. That'd be more cost effective than buying all the new gears I can find, and (if I can actually find a good core) I'd end up with 100% good gears instead of 60% good gears.

Only trouble is I'd have to pull the transmission first before I could remove the cover and inspect the gears to make sure they're in good shape. And anyone who's pulled a transmission in a salvage yard (no jacks allowed) knows that's neither easy nor fast. It's a dilemma alright.

 

[97Sandbox]

I think I've landed on getting a full seal, bearing, and synchro ring kit for both of my transmissions. New input shafts for each as well, hopefully I can get both set up with the shims from one pack. The 4x4 needs a new 1-2 shift fork, reverse gear, and 5th/reverse slider.

I'm on the fence about replacing the 5th gear in the 4x4. It shows some wear, but not too bad. I'll probably go ahead and replace it.

I'm also thinking I don't need to do all the needle bearings because they look and feel good. From what I understand, they seldom fail at the rate of the shaft support bearings or the gear teeth. But maybe I should just change them while I'm in here.

Both transmissions will get new shifter bushings and top seals too. I had one kit on my shelf and will pick up another.

Before tax, it's looking like almost $1400 in parts...ouch.