Hello Everyone,

About 1000 miles ago I had to rebuild my rear Turbo diff since there was a lot of play and wear on the pinion shaft, unloading it during coasting. It is beginning to feel like there is a bit more slop in it again, and under coasting it sounds slightly louder too, which has me concerned.

I tried to follow the FSM and some general ring & pinion online guides to interpret the tooth patterns, and use that to choose the correct pinion spacer thickness. The biggest thing that seemed to be important for used gears was to try to center the wear pattern between the root (base) of the tooth and the crown (tip) for the coasting side, at least for setting the pinion depth.

At the original pinion depth, after taking out the slack in the pinion, I had:



To my un-trained eye anyway, this looked like the pinion was too far away from the ring (too shallow), which would be consistent with bearing wear on the pinion being the culprit for it loosening up. A thicker spacer did seem to move the patterns more towards the middle of the tooth (from root to crown), but gave these oddly pointy patterns:



Additionally, setting the backlash seemed to be pretty straightforward and measurements all around the ring gear were consistent (0.07mm to 0.11mm). The other question that I had and couldn't seem to find an answer to was how tight to make the non-ring-gear adjuster up against the bearing race? I got it about as tight as I could with a pair of needle-nose pliers turning the adjuster, and it didn't seem to affect how easily the diff spun, so it seemed OK, but I'm reconsidering that now.

So, what do the experts here say about these patterns, and about how tight to make the diff adjusters inwards on the diff?

Thank you!

 

Nice photos! As you've indicated, the gear contact pattern can use some improvement. So, I'm not exactly sure what you're trying to doing. If you're only replacing the bearings, than there's really no need to change the pinion depth from its original setting. You need a dial indicator to set ring gear backlash. I assume you already have a dial indicator. Not sure what you mean by "non-ring-gear adjuster "? Are you referring to setting the side bearing preload using the adjusting screw in the side bearing caps? As the FSM shows, you need a large micrometer (8"-9" for turbo) and tighten the adjusters equally until the distance between the pilot sections on the bearing caps are within the specified tolerance.

 

I had originally torn it apart because it was making awful noises on deceleration at any speed, and coasting at low speed there was a "grinding gravel" type noise too. I was expecting a lot more carnage than I saw, but basically the pinion shaft had a LOT of fore-aft play, indicating that there was a good deal of bearing wear, or that the pinion lock-nut had backed off or something. When I opened it up, all the bearing surfaces still looked smooth and consistent so no bearings or races were replaced.

I used a dial indicator to set the ring gear backlash, basically by moving the side-bearing adjuster on the ring gear side in or out since this is the side that forms the "stop" that the ring gear will move out to when under load. Once that was moved, then I would move the non-ring-gear side adjuster in until it was snug and then check the backlash. I didn't check the distance between the pilot sections on the bearing cap since I had no idea where to find a micrometer that big, especially to rent since I don't really have any other use for it, but now I'm worried that not doing this may be leaving too little preload on those bearings, especially as things heat up.

 

Just do a Google search. You can order an 8-9" micrometer online for cheap (https://www.higherprecision.com/prod...ies-8-9-inches). Of course, most of them are Chinese junk but they worked well enough for me. I installed a new clutch type LSD with 4.3 R&P on my 90 RX7 about 15 years ago and haven't had a problems since. If you want a quality Starrett mic, than that'll cost you 3x-4x more.

 

Also, I was going to mention that with the long pinion shaft it's not uncommon for the pinion bearings to get starved of oil and eventually fail. That's why I'd recommend using a high quality synthetic gear oil.

 

Oh, thanks a lot - I'll pick one of those up and maybe take it apart next weekend to go over everything - it should have about 1500 miles on it then so I would be changing the fluid anyway. I was using Royal Purple 75w90 synthetic since originally rebuilding the diff back in 2012 when i put a torsen LSD in there, so there shouldn't be any specific additives necessary for clutches etc. Since that first rebuild, its been around 20k miles, but I had a suspicion for most of that time that things were looser than they should be, so I'm trying to avoid that this time around.

 

Hey did the adjustment to the diff solve the noise while decel and coasting? Or did you have to rebuild. I'm having the same issue which is why a took it apart.