Details on the Rearend: 88IrocZProjectCar

I have a 10-bolt from a 91z28 with about 37k miles on it that I started working on 20+ years ago for this project. Project objectives changed and I'm going back on work I did on the rear end years ago and didn't document or can't remember details.

I was taking the Summit aluminum cover off to replace with a stock looking cover and noticed I may not have completed the installation I started in early 2000's. For reference here, I took the differential apart to replace the stock Z28 limited slip carrier for a SLP take-off that I purchased back then. I wasn't changing the stock 3.23 ring and pinion, so the pinion was left un-touched.
Back to current day, I turned the pinion yoke, and it turned way too easy with ring gear, carrier and axles installed. I didn't have the appropriated torque wrench to check total rotating preload, so I went out and bought a new Performance Tool 80 in/lb deflection beam torque wrench. Here's the differential as found after removing the Summit cover:


SLP Torsen carrier as found after installation from around 2000.

I checked the total axle preload on the pinion and was only getting 4-5 in/lb rotating torque. You can see from the pattern check (from 20+ years ago) the pinion depth seems pretty good. The caps were torqued, so I assumed I had installed the shims with preload and when took the caps off there was some pre-load because it was hard to get the carrier and shims out. After doing this I checked the pinion only preload, and it was only 4-5 in/lbs, the same as the total axle preload, so obviously I decided I had to go through the whole setup process again. To be honest my memory isn't what it used to be and I have been reading and watching YouTubes hoping to refresh my memory of how to set-up a 10-bolt and answer all of my questions. Unfortunately I haven't found the answers to a couple of questions.

FYI, this is one YouTube video from a shop teacher that explains stuff really well that I thought might be of interest to someone: !0-bolt Instructional Video

The thing I've been search for is the answer to whether you can just tighten the pinion nut on a used pinion where the bearings have obviously worn in and preload changed. I've seen many opinions about changing seals and re-installing pinion nut and mark or torque it back without removing pinion and putting in new crush sleeve. Many repair shops do seal replacement without taking whole differential apart to put in new crush sleeve but reuse pinion nut and just torque it back to the used preload values. I haven't loosened the pinion nut, it's actually painted over with Por15, so I doubt it loosened up itself. I've already tightened pinion up some, I got the pinion nut preload to ~8-9 in/lbs, my 88 GM Camaro manual calls out for 10-15 in/lbs for used bearings.

Is this acceptable to tighten the pinion to get more preload without using a new crush sleeve, and if so, should I take it up more to get above 10 in/lbs?

I went through the process of shimming the carrier first with no preload to set backlash which I tightened up from where I found it at ~0.009" down to a tighter 0.007" of backlash. After getting the carrier shimmed to a snug fit I added ~0.004" per side as recommended by the manual. I ended with 0.236" on both sides, which is the same overall shims total I had from install in year 2000, except that had 0.237 on one side and 0.235" on the other. So the current setup tightened the backlash as noted above. I put the axles back in to check the total pinion/axle preload and it was only ~12 in/lbs. The manual calls for 35-40 in/lbs on new bearings and 20-25 in/lbs on used bearings. I already said the pinion bearings were used because I never took pinion out, but the Torsen carrier had new bearings.
According to the shop rebuild video link I attached, the preloads are the most important aspect of the rebuild process, the gear pattern contact is important to, but mostly to get that ring and pinion contact centered as much as possible.

Obviously, my total axle preload is way off, 12 in/lbs instead of 20-40 in/lbs.

Where should I go from here, leave pinion preload as is and add more shims to carrier?
Try to tighten the pinion preload more than add more carrier shims to increase total preload?
Take out pinion and install new crush sleeve or new crush sleeve and bearings to reset pinion preload than continue with adding more carrier shims to increase total axle preload?

Any opinions especially from any actual career mechanics or guys that have done a lot of differential work much appreciated. I've worked on cars and motorcycles over the years, but haven't done any differential repair other than this one 20 years ago and now.

 

4 -5 in-lbs preload on the pinion is nowhere near enough. Should be more in the 25 range with the seal installed.

Yes you can just tighten the nut, if it's never been tightened enough. No you don't need a new crush sleeve, if the old one hasn't been crushed yet. As long as it takes the usual 150 - 200 sort of ft-lbs on the nut to turn it, it's good to go.

I like to use more than .004" of extra shim per side on the carrier to preload its bearings. .237" & .235" largely passes the smell test as far as that goes. So, my recommendation would be, pop the carrier out, tighten the pinion nut as described, and add more carrier shim if possible. As much as you can. I don't think it's realistically possible to put in "too much" carrier preload. It is DEFINITELY possible to have too little backlash however; this is because the gears GROW when they get hot, meaning, backlash goes away in operation. And if it all disappears, then you have 2 chunks of metal attempting to occupy the same volume, and we all know how poorly that works. I like to have all the preloads toward the high end of their spec range so that everything is solidly secured in place, and the backlash also toward the high side at like .010" - .012". An extra .001" or 2 even above spec won't ever be noticed, but even .001" too little can result in disaster.

 

I just tried re-torque the pinion nut, won't budge at 200 ft/lbs. The guy that owned the car this rear axle came out of said he had ~$600 work done at dealer in 1998 and said they replaced one axle. He totaled the car in a front-end collision, and I bought the rear axle in 1999. I doubt the ring and pinion was removed if it was just an axle problem. I'm assuming if the ring and pinion are original, and
this was installed and torqued correctly in 1991 when built, the bearings must be worn out since there is so little preload, do you agree? I think I already know the answer, but do you agree I should just take the pinion out, replace bearings, seal and pinion nut and reinstall with a new crush sleeve? I did buy some new Dorman Axle c-clips as one looked like it has a slight groove in it. Not sure what the purpose is but the c-clips look copper plated. The ring and pinion looked fine to me, didn't notice any chips or indications of gear wear, so I should just be able to reuse the existing shim and hopefully the pinion depth should be close? Even though I worked on cars my whole life, I question myself more than I ever did when I was young and wonder if I should just take axle to a shop and have it done? Or am I making too big a deal about this? Any wisdom, opinion or comments appreciated.

 

Not a particularly good idea.

No way to know that.

The problem basically is, you have no idea what you've got. Note that I used alot of the word "if" in my reply about that sort of thing; butt it sounds to me with the addl info like this is just an old wore-out stock rear, such that odds are, the bearings are original.

So yes, safest thing to do, would be to replace all the bearings. Yes you can re-use the same shim thicknesses: shims go with the housing, not the moving parts, so as long as you're using the same housing, the same dimensions apply. That is, the parts are precise to within a .001" or 2, butt housings are all over the place, which is why shims are needed. If you imagine a set of moving parts (pinion, carrier, gears, etc.) all just hanging out in space somewhere all set up perfect and just right, and you want to come along and drape a housing around it all, the shims adjust the housing to fit the parts. Not the reverse as might seem intuitive.

Press the old pinion head bearing (think of it as a tadpole with a head and a tail) off, and measure the shim. It's probably .035", at least every one I've ever taken apart was. Evidently the factory got the pinion bore machined into the housing fairly repeatably, unlike the carrier bearing bores. Whatever it is, put a new shim the same thickness back in, and press on a new bearing. Grease it a little with either some white lithium or Mobil1 synthetic or even just some synthetic gear lube before assembling it into the housing. Do the same to the tail bearing in the following steps.

I STRONGLY recommend using a solid spacer https://www.summitracing.com/parts/rat-4111 rather than a crush sleeve. Also, get an additional tail bearing for the pinion, and hone it out with a brake hone so that it slides onto the pinion easily; then put an unmodified bearing on for final assembly. The way the crush sleeve works is, you put the pinion in with all the shims and the honed tail bearing and no seal, and guesstimate the end play in it; then take it all back apart and take out a little less than that much shim; repeat very carefully in small increments until the end play goes away; continue repeating until you get the desired preload (ideally 22 - 25 in-lbs or so). A little too much preload is better than not enough, so let's say you get 21 but the next possible thinner shim stack gives 27, go with the stackup that gives 27, but don't let it ever get over 30 lest you wipe out the bearings. Then take it apart one last time, put the unhoned bearing and the seal into the housing (don't forget to put the bearing in BEFORE the seal, and use a BFH and a block of wood and one mighty whap to install the seal; DO NOT try to tap it in around the edge, it will leeeeeek EVERY TIME if you do that); and assemble it one last time. With the spacer you can tighten the holy living bejesus out of the nut until it screams for mercy, you don't have to quit tightening just because some sleeve got crushed enough. Personally I use about a 4' piece of bar stock with holes drilled to bolt to the yoke near one edge such that it doesn't interfere with getting a socket on the nut, and about a 3' piece of pipe on the handle of the biggest breaker bar I have. No idea how much torque all that can generate butt I will say, it'll crush a crush sleeve like it isn't there, so it's probably capable of 300 ft-lbs or more.



Then put the carrier in like I posted previously. I use 2 big C-clamps on the carrier bearing outer races, put the shims in the housing, tighten the clamps until I can just barely get the carrier to go in with the shims selected for an extra .010" on each side once I've got the backlash I want, and drop the carrier in. Shims come in the form of, 2 .100" per side, then abuncha thinner ones; put whatever thinner ones you need between the 2 thick ones, to keep em from getting munged during installation.

I'm not worth a crap at evaluating gear "patterns" myself. I've tried butt it never makes sense to me in the sense that I can look at it and know how much or which way to adjust the pinion shim or the backlash or it even comes out the same 2 times in a row. I don't even bother anymore. Seems to me, if I put em together as described, they work fine no matter what the "pattern" looks like.

If the C-clips had grooves the axles are probably worn there too. And if they're worn there, they're probably worn where the bearings ride on em, and crappy butter stock axles are AMAZINGLY easy to bend by curbing the car, speaking from personal experience at about 2 mph on black ice. Wouldn't be a bad idea to just launch a preemptive first strike on em in any case while you've got it apart. https://www.summitracing.com/parts/aly-12103 Also wouldn't be a bad idea to stiffen the whole thing up so it lasts as long as possible. https://www.taperformance.com/prodde...p?prod=TA_1809

 

I took the pinion and axles out and inspected them. I checked back at the Carfax I had from the doner car the rear axle came out of and realized I forgot and stated some info wrong. The estimated 37k miles was on the rear axle work done, not the original car mileage. The actual car before it was totaled had almost 114k miles, so the pinion bearings that seemed to be original, were looser than the new bearings but nothing stood out as extreme wear. With that said I am replacing pinion bearings, seal and pinion nut. I already removed the bearing halves out of the differential. I'm curious what you method of removing the pinion bearing without destroying the bearing is? I don't have a bearing separator so I'm probably going to buy one from Harbor Freight. I would rather use a press to get bearing off, but I don't have one. Harbor Freight Bearing Separator: LINK has a puller as part of the set, but I'm concerned that the threads won't handle a lot of torque if the bearing is on super tight.


I bought a SA35-2015 overhaul kit when I bought the SLP Torsen take-off posi carrier back in ~2004. I only used the carrier bearings so I have the pinion bearings, seal and pinion nut, but it has the crush sleeve. I don't know if you read anything about my 20-year-old project car, but I changed direction and I'm going back to mostly stock. Is there any really good reason to go with a solid spacer on a stock motor and gear. I'm older now and don't plan on taking this car to the strip or anything so not sure if the solid spacer adds anything.


I was able to get a little more torque on Pinion nut with this setup before it stopped at ~200 ft/lbs These tools are only ~2' long, but my highest ft/lb torque setting on this rachet only goes to 200. To get much more torque you'd probably have to go to a 3/4" drive torque wrench. In the GM manual service manual ST-368-88 specifically for the 10-bolt, they don't give a pinion nut torque value for the crush sleeve, it only says to tighten nut until there is no end play and carefully tighten up until you get the appropriate preload for new bearings of 20-25 in/lbs. The link you gave for a solid spacer has in the "Notes" to torque nut to 125 ft/lbs, so I don't know if I need anything bigger than what's shown below. The total assembly preload for new bearings is shown as 35-40 in/lbs.




It looks like if you have the pinion depth right, the contact is centered between root and face off tooth. The backlash just moves the contact between the heal and toe of the tooth. I found out if you don't have some load on gears, it doesn't give you a good contact pattern.




This was the best advice as I really didn't take a close look with a magnifying glass or do any measurements. The c-clip groove on the older axle looked worn, and the splines weren't as nice as the newer axle from the axle work mentioned before. So it just so happens, that I have a set of Superior axles that were for my original build planes, that I had posted for sale, but have now taken off as I will use those. I am trying to keep the car looking stock, so I just removed and sold the Summit aluminum cover and replaced with a Yukon OE looking cover. I don't know how thick the stock cover was, the Yukon cover seems pretty thick, so hopefully give a little more support than stock. Later I will follow-up with pictures of my axles and why I decided to change them after inspecting them. I thought it would be useful for newer members that may decide to work on their own differential like me. I always look at YouTube and pictures because it easier to me than reading text online or in a manual to do things you're not familiar with.
Thanks for your input.



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The pinion should come out of the head bearing with a little gentle persuasion and tickling. Be EXTREMELY wary about wailing on it with a BFH though; the thread part of it isn't hardened anywhere near like the gear parts, and it's possible to mushroom the threads that way, to where a nut won't even go back on. Of course that destroys the pinion. Use a jaw-type puller around the pumpkin to press it out.

Getting the tail bearing off, OTOH, I know of no way to do that, and preserve the bearing. Usually I end up cutting the cage and setting the rollers free, then use a splitter on what little collar there is at the top of the inner race, in a press. Another way of doing it is to wizz-wheel 2 deep grooves in the inner race opposite each other and split it with a chisel. That's a bit risky though, as sharp pieces of metal go flying off at great speed.

Yeah; like SHE always says, you don't have near enough tool.

Actually, 2 really good reasons: it's not a one-and-done deal like a crush sleeve is, such that you don't need to have a well-stocked stealership parts dept to go pull another CS if you have to take it back apart for whatever reason; and more important, thrust in reverse pulls the pinion into the case, which tends to crush the sleeve some more. That's DEATH, because when the sleeve gets crushed without the nut tightening down on it, it is no longer supplying any force on the nut trying to hold it still. Remember, that's ALL the crush sleeve does, is give the nut something to tighten down against to keep it from backing off. They used to use cotter pins, exactly like a front wheel bearing. (which of course a pinion bearing set is IDENTICAL functionally to a FWB except that the shaft spins and the housing sits still whereas in a FWB the shaft sits still and the outer spins) In fact, as late as the mid-late 50s "classic" trucks, that rear still used a cotter pin. Butt with the much higher speeds possible with a V8 as compared to the old sufferin' six, it's too easy to shear a cotter, so they went to the CS system. Meaning, once the sleeve crushes ANY more, the only thing holding the nut on is the nyloc; and since that's only about 30 or 40 ft-lbs in that size nut, it has NO chance of staying on if that happens. The solid spacer is simply BETTER in every way.

Yeah I know all about what the book says the pattern is supposed to show; and it makes sense, as far as that goes. I've never been able to get one that was consistent enough to trust, like, I'd put it together and look at it, then take it back apart and make a change that was supposed to have some particular effect, butt it didn't; and then when I put it back together the way it was before, it was different yet again. I just don't trust it. And yes, you do have to "load" the gear teeth somewhat, to get a clear one; jamming a tire tool down in the works seems to do the trick.

Yes Ratech says 125 ft-lbs butt the last time I was over there, they told me I could tighten it as much as I want. Since it's all metal-to-metal, with nothing that compresses or anything like that, once it's "tight", tightening it further has no effect until it's SO tight the threads strip, except for making it less likely that it'll fall back off on its own.

That's correct. With the seal installed. Seals are inconsistent though, which is why I prefer to set them up without the seal (using the solid spacer), then when I find the correct spacer thickness, install the unhoned tail bearing and the seal into the housing, and put the pinion in one last time.

If you really want to try to fine-tune the pinion shim using "patterns", then get another head bearing as well, and hone it out like your "test" tail bearing; and put the unhoned one on only for final assembly. All of which is yet another good reason to ditch the one-time CS and go with a solid spacer; you could easily pop off 4 or 5 CSs setting a rear up, maybe more, if you had to select shims and all that.