Great advice (about Jack Transmissions). But I'm stubborn and stupid. I already wasted $400 getting a shop to not get it right. So now I'm tearing into like a fool. Bought a press, measuring tools, made my own tool to turn the threaded carrier nut thingy, mustardy stuff,

Looks like you can get Shim in a Can from Amazon. What is the best method to cut it? Aluminum is nice because I just use the spacer as a template and cut it with a knife. Aluminum will really compress? I'm not pressing a new bearing down 10tons. I'm using an older bearing with the inside shaved a slight amount for a slip fit.

I am loading up the carrier as I turn the pinion. I read the drive side since this is a brand new gear set.

OK cool re: loading the carrier and reading the drive side. And that sucks about the shop, sorry to hear that.

You can cut steel shim up to about 0.010" with sheet metal shears. Trace the outside and inside circumferences of the race onto the shim material, cut the outer circle, then gently fold in half (don't crease) and cut out the inner half-moon shape....unfold and you have your shim.

There will be expansion and contraction of the entire pinion assembly over time, along with the case, which will likely allow for a slow, creeping deformation of the aluminum over time. There are some aluminum alloys that are suitable for shimming, but I'd guess that the easily produced baking foil is not that alloy. I cannot say from direct experience that this will definitively happen as I never saw an aluminum shim in anything I rebuilt (definitely not an OEM shim), but in my other life as a jeweler/metalsmith I can attest to common Al being far more ductile/malleable than carbon steel. I would not trust it in my own diff.

You have a press but are not using it to install the bearing races? Or have a new bearing and are using the shaved old inner races as tools to press on the new ones? Not sure how to read that, and didn't look far enough back to see if you bought new bearing.
If the latter: Great!
If the former: How much of a slip fit is your inner race? Loose enough that it drops on, or do you still have to force it? Loose enough that once in place it has the tiniest bit of play? The inner race is designed to stay securely set in place after having been pressed onto the pinion shaft, and any movement (spinning, side-to-side) will result in a small amount of float in the pinion shaft, promote galling at the shaft/race location, and begin the degradation of the bearing rollers (pitting/spalling). It's really not a great idea to allow a tapered bearing inner race to slip into place unless it requires heat to overcome the interference (around 175-200*F). The outer race shouldn't have any movement, either, but often does not require a press-fit (tight slip is OK as long as it does not move). Apologies if you knew all of that...I wanted to get it all out in one shot haha.

Thanks for the additional info. I am just using the aluminum as temporary shims to space it and read the patterns. My plan was to buy the correct OEM shim. I have discovered a new frustration that is leading me to call up Jacks Transmissions tomorrow. I've got a contact pattern that I like, but it is past the available Mazda shims. The shims they produce end at 3.5mm and I'm at 3.62mm.

All along I new that this pattern being WAY off the top edge was a problem. And that adding the large amounts of additional shims seemed excessive. So I'm stuck and need to call in the pros...

Uploading a progression for your review. 3.19mm spacer (original setup), you can see that the pattern is too high. Need to raise up pinion.

https://cimg9.ibsrv.net/gimg/www.mia...6ab0fdc300.png
3.19mm spacer

Here is a big jump (the pattern didn't start moving until I jumped way up). This is covering the entire face.
https://cimg2.ibsrv.net/gimg/www.mia...2191a0e5c1.png
3.51mm spacer

3.62mm spacer pushes the pattern a little too low.
https://cimg5.ibsrv.net/gimg/www.mia...26a4b6d6bd.png
3.62mm spacer

Should I just go for the max spacer available (3.47mm)?

OK! Julio sent me some nice steel shims (.1mm, .15mm) that allow me to accurately march the pinion gear up while taking some images. THANK YOU JULIO!

Tons of good info online. But I particularly liked this explanation.
https://www.differentials.com/techni...-instructions/

Here is my process. Install all new bearings. Do not install the crush sleeve or pinion seal yet. The pinion seal will give you erroneous running torque measurements.

1. install pinion shim (going from 3.23mm to 3.5mm)
2. press pinion assembly in by tightening pinion nut until achieving 10in-lbs running torque on a beam type torque wrench
3. Install ring gear carrier.
4. Adjust screw adjusters to achieve .003" backlash on the ring gear.
5. Make certain the ring carrier preload is solid. This means, make sure there is no play (axially, not rotationally) in the carrier.
6. Torque down bearing cap bolts
7. clean off all gear marking compound
8. Take image (of exact same spot on ring gear)

3.13mm is my original spacer for the 4.1:1 gear set.

https://cimg4.ibsrv.net/gimg/www.mia...dae925e4f0.jpg
3.23mm pinion spacer


https://cimg7.ibsrv.net/gimg/www.mia...d1c38e3925.jpg
3.29mm spacer

https://cimg9.ibsrv.net/gimg/www.mia...e7977f744a.jpg
3.39mm spacer

https://cimg0.ibsrv.net/gimg/www.mia...c7558e6328.jpg
3.47mm spacer (Mazda p/n: 022327415A)

https://cimg2.ibsrv.net/gimg/www.mia...d56ec3066f.jpg
3.5mm spacer

I went with 3.47mm because, above that, a strong crease in the pattern appears near the bottom of the gear ("toe"). It just gets worse as you move higher. Next you have to re-assemble with the crush sleeve and pinion seal. This time you have to use a breaker bar and solidly mount the diff assembly into a vise.

https://cimg8.ibsrv.net/gimg/www.mia...824c061d82.jpg

So this is buttoned up in the car and I'm breaking it in. My initial impression is that the drive whine is nearly non-existent and the coast whine is definitely there. But I can see how this coast whine will likely slowly go away with wear.

Some may ask why I stopped (landed) on 3.47mm. That is the thickest spacer that Mazda makes. I didn't feel very comfortable getting outside of the OEM range. I don't feel very comfortable with the pattern on the drive face. I am not seeing a nice wide impression that is centered without any impression against the top and bottom of the face. But I guess this is how these gears are cut.

This was a hell of a lot of work and hopefully these notes will help the next person to do this. Honestly, I can't recommend doing the work yourself. But I did learn a ton and have some new tools.

I wouldn't really be afraid to go outside of what Mazda offered since they're not Mazda gears. I'd default to keeping the pattern happy over what is available OEM from Mazda. That said, your final pattern doesn't look bad, if anything I'd take a hair of lash out at that pinion height.

question to anyone who has repaired a diff. I never like the 'tower to tower' measurement (7.301") to be the way you'd set the carrier bearing preload. I can only see that working if every single part in the diff is brand new. Even the case.

So I had to take the whole damn thing apart. It was making a clunking noise when shifting between reverse and 1st.

Turns out the carrier preload was way off, loosened up. So loose that I could turn the side bearing thingy with my fingers. Check the measurement, 7.301... in spec and of course still had the retainer in place. That clunking noise was likely the entire assembly shifting in the case.

The backlash was also loosened up to about .006-.007. But that doesn't seem that bad in hindsight.

Also, the gear set has worn down some. I found some light metal in the oil that turned it a solid grey color. I called MFactory and they said it was OK, and that it really should not matter as long as the gear faces were OK.

Anyways - I'll take some photos and include yet another image of the yellow goo pattern.

If you can visibly see that the gear face has worn, as in a step in the metal from wear the gears are shot. Especially if they aren't shiny and have a matte look to them. A little bit of glitter in the oil is normal, turning the oil gray from it not so much. Sounds like you just ate the gears up and that's the clunk you're hearing, I would expect your back lash to open up more if that's the case though.

we’re still waiting on those photos sir.