M5R2 (M5OD-R2) Rebuild Deep Dive

[97Sandbox]

Okay I was all wrong for the output shaft bearing, it's actually super easy. When you remove the snap ring from the third gear side, the 3/4 synchro assembly, third gear, and needle bearings all just lift off. Then you can rest the back of second gear on the cradle of a press, and press on the first gear/output side of the shaft. This effectively pushes the shaft through the first and second gears, the 1/2 synchro assembly, and the output shaft bearing. I'll make a point to take pictures when I do the 2wd.

I got the countershaft front bearing race off too. I really snugged the separator down and just kept cranking. It got a little nerve wracking, but eventually the race "popped" and it came off easily from there.

Now it's time to clean the shafts, gears, and sliders. Then I can start reassembly with fresh brass rings and bearings. I think that should all go pretty smoothly as long as I don't get anything mixed up.

The only other tricky disassembly I have to do is for the shift tower to get the 1/2 and 3/4 rails free so I can swap the 1/2 fork. That'll deserve it's own section.

 

[allmyEXes]

You've got me curious. I looked for a drawing or diagram of one and came up with an 18 page PDF document. M5R2 diagrams

 

[97Sandbox]

Yes, that looks like the one I found too. Lots of good info in there!

 

[97Sandbox]

Got new races onto the countershaft and the bearing pressed onto the new input shaft. Then I started working on the output shaft and ran into something that made me pause.

The second gear and 2 side of the 1/2 synchro assembly are totally different between the 1997 output shaft assembly that came out of my transmission and the 1999 output shaft assembly that I grabbed from the salvage yard. The 1997 parts are pretty simple, just one brass synchro ring and symmetrical teeth on the gear.

But the 1999 parts have two brass rings and a steel ring between them (they all nest between the gear and synchro hub) and they engage second gear differently than the 1997 setup. Also, the 1999 second gear has asymmetrical teeth, basically a mirror of the third gear teeth.

I've never read about this later-revision second gear and synchro setup. Both second gears have the same tooth count, so I think the overall output shaft assembly is interchangeable. Unfortunately, my rebuild kit doesn't include the parts to replace the brass rings in the later assembly.

Since the 1999 parts are in so much better shape, I think I'm going to use them, even though I'll have to run with the used brass rings. I don't think a new brass ring in the 1997 assembly will help much because the gear teeth and synchro slider teeth that would engage it are all chewed up. I'm also hoping there was a good reason why Ford/Mazda switched to a more complex and surely higher-cost design, and I get better shifting as a result of it.

It'll be interesting to see which setup is in my 1998 2wd transmission when I dive into that next!

 

[97Sandbox]

Sure enough, there's a different synchro ring kit for later transmissions.

M5R2 TRANSMISSION SYNCHRO RINGS KIT WITH 3-PIECE 2ND RING FITS '99-'08 F150

FORD M5R2 TRANSMISSION SYNCHRO RINGS KIT WITH 3-PIECE 2ND RING FITS '99-'08 F150 (SRK248C

www.transmissionpartsdistributors.com

It's out of stock though, so I'm sticking with my previous decision to forge ahead with used second gear synchro rings.

 

[410Fortune]

So now that you are inside th slush box maybe you can help me understand my synchro issue
In my sport trax, no idea what year the m5od-r2 is or how many miles
Sucker shifts great until it gets warm… after a highway run shifting into third gear gets grindy… it gets worse and worse until basically I cannot downshift into third because it just grinds. I can force past the grinding… but after a few years of this it’s getting worse

Is this a synchro issue you think?

Keep up the good work! I have two of these transmissions right now for my own personal al use… with my luck I grabbed the one with the 3rd gear grind hahahaha
Any way to tell what year they came from just by looking at them?

 

[97Sandbox]

That does sound like a synchro issue, at least in part. Something probably getting hot and causing part(s) of the 3/4 synchro assembly not to move the way it should.

Since the 3/4 synchro moves between the last gear of the main shaft (third) and the only gear on the input shaft (fourth), there's a lot going on there. There's a caged roller bearing that runs on the front of the main shaft and inside of the back of the input shaft. There's a thrust bearing there too. If the input shaft front bearing is worn (they usually are), there'd be more load transfered to that roller bearing. My guess would be that it's building up heat, things are expanding, and clearances are getting too tight as you try to slide off of fourth gear and into third.

But it's probably a combination of things. I think that 3/4 synchro is especially prone to wear since it slides between gears that aren't on the same shaft. That roller bearing should keep things concentric, but as parts wear, I'm sure things get sloppy and start to move in ways that they're not meant to.

That said, I know very little about transmissions and I'm not a mechanic. Just my best guess after staring at parts for hours haha.

 

[97Sandbox]

Pressed on the output shaft bearing.

I've been able to do all the bearings with just two pieces of sch. 40 PVC and the old races.

Third gear, the 3/4 synchro assembly, and the thrust bearing get held in by a snap ring.

Then put on the roller bearing that @410Fortune likely cooked in his 'trac.

And drop it all into the case. Don't forget to slip on the 4th gear brass ring first (I did...oops).

Then you can wrestle things around to get the shafts where they need to be as you slide in the front and rear/mid bearings and races. This took some patience and finesse.

Then reinstall the plate over the rear/mid bearings to hold them in.

The front plate will come later.