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I am in the process of installing an RX8 4.44 ring and pinion into my diff. I am reusing the RX8 pinion bearing and races because they are in good shape and the pinion depth is correct but I am not sure how to set the pinion preload since I am reusing the old bearings. The service manual states that it should be 12-15in lb but when I checked the preload before pulling the pinion from the RX8 diff, it was only about 1-2in lb. I am assuming the bearings have seated in the 100k miles that is on the diff so now it is very easy to turn. The question is, should I still set the preload to 12-15 as if they are new bearings or should I set it to 1-2in lb since the bearings are already broken in?
Just nip it up so it reads the same as where it was before disassembly and it will be fine, if you tighten it up to spec it'll likely kill the bearings.
I replaced the crush collar and bearings in mine when swapping in a 4.44 ring and pinion but if I was to do it again I'd likely reuse them like you're doing.
Thanks for the input Ceylon. I found some Dana rear end setup specs that specify 12-15inlb of preload for new bearings and 6-7inlb for used bearing so I think I will go up to 6 and call it a day. www.differentials.com also states that it should be 50% less for used bearings.
One thing I've learned after doing gear swaps for awhile is that doing a one off gear swap the right way is expensive. I'm not saying you shouldn't just shore it up and run it - if you're on a budget and you want to re-use the bearings, and you think your pinion depth is going to be right in a different housing with the same pinon shim, well go ahead and try it but don't be surprised if the housing tolerances are way different and your pattern is off/gears whine/diff eats itself.
To get a good pattern with the right bearing pre-load you need to ruin a set of new bearings (or the old ones if you don't destroy them taking them off) to make setup bearings. You should have a master shim kit on hand too so you can swap them quickly to get to the right gear pattern, I don't think I've ever seen a situation where swapping gear sets, or the carrier didn't have some change in pinion shim to get the right depth.
One thing I've learned after doing gear swaps for awhile is that doing a one off gear swap the right way is expensive. I'm not saying you shouldn't just shore it up and run it - if you're on a budget and you want to re-use the bearings, and you think your pinion depth is going to be right in a different housing with the same pinon shim, well go ahead and try it but don't be surprised if the housing tolerances are way different and your pattern is off/gears whine/diff eats itself.
To get a good pattern with the right bearing pre-load you need to ruin a set of new bearings (or the old ones if you don't destroy them taking them off) to make setup bearings. You should have a master shim kit on hand too so you can swap them quickly to get to the right gear pattern, I don't think I've ever seen a situation where swapping gear sets, or the carrier didn't have some change in pinion shim to get the right depth.
I was prepared to go through the full process of shimming the pinion and replacing the bearings but there is no reason to go through the extra hassle and parts if the specs are dead on. I measured the pinion depth of the RX8 diff before I pulled it apart as well the RX7, then I measured the pinion depth of the RX8 pinion in the RX7 housing. The pinion depth measured exactly the same on all 3, literally to the 1000th of an inch. I still need to install the carrier and check the gear pattern. I will upload some pictures of the pattern when all is said and done.
I was prepared to go through the full process of shimming the pinion and replacing the bearings but there is no reason to go through the extra hassle and parts if the specs are dead on. I measured the pinion depth of the RX8 diff before I pulled it apart as well the RX7, then I measured the pinion depth of the RX8 pinion in the RX7 housing. The pinion depth measured exactly the same on all 3, literally to the 1000th of an inch. I still need to install the carrier and check the gear pattern. I will upload some pictures of the pattern when all is said and done.
This was my experience also. I had quite a few diffs apart at the time and all the measurements were identical making the swap dead easy on the fd!
Quick update for anyone that may need the information in the future.
I ended up using the old rear pinion bearing and race from the the rx8 with the old front bearing and race from the rx7. The pinion depth came out perfect and I preloaded it to 5in lb. I ended up having to buy some different carrier shims since both the RX7 and RX8 shims were giving me too much backlash. Also ordered and replaced the carrier bearings since there was a chance that I mixed up the left and right races. I measured the bearings individually and the whole carrier assembly with the bearings installed and it came out ever so slightly thicker (about 0.03mm total), I am assuming it is because the bearings were not seated yet. The backlash came out to 0.032 - 0.042in which is within Mazda spec. What's interesting is that I measured the RX8 backlash prior to pulling it apart and it was out of spec (0.034-0.056in) probably because the gears had worn down over time. The gear pattern is slightly closer to the toe which should be perfect since the pattern will move up to the middle once there is a load on the gears.
03-01-21, 11:03 PM
