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So I blew my 10 bolt a week after getting my car back from the tuner. The rear grabbed weird while starting a burnout, and a deadly amount of wheel hop broke a few teeth off the pinion. I’m installing a fresh Eaton torsen, along with a set of 4.10’s I had laying around. I can’t swing an 8.8 right now, I just want the car running till the end of the year to enjoy the cooler months.
This is the pattern I got with my first mock up. What do you think about the pinion depth? I looks to be a tad towards the heel, should I try to get it a little closer to center? I still have to shim the carrier for backlash, right now it’s at a loose 16 thousands, hopefully getting that around .008 will bring the pattern deeper towards the center. Just looking for any insight/suggestions for setting these up close to perfect. I’m also using a crush sleeve eliminator, and I have preload on the pinion set to 15 inch lbs. Really don’t want any gear whine, thanks.
You are wasting your time doing a pattern check before the backlash is set. I'm assuming by the look of the pattern that this is a used gear. You are also wasting your time by doing a pattern check on the drive side of a used gear. When setting up a used gear the coast side is going to give you a more accurate pattern. The drive side pattern is going to look weird because of wear on the teeth. Set the backlash and do a coast side pattern check. Turn the differential about 5 times in both directions with an axle when doing this and post pictures again.
You are wasting your time doing a pattern check before the backlash is set. I'm assuming by the look of the pattern that this is a used gear. You are also wasting your time by doing a pattern check on the drive side of a used gear. When setting up a used gear the coast side is going to give you a more accurate pattern. The drive side pattern is going to look weird because of wear on the teeth. Set the backlash and do a coast side pattern check. Turn the differential about 5 times in both directions with an axle when doing this and post pictures again.
thanks, I’ll set up the backlash after work and post back.
Ok got my backlash at .007 Drive Side Coast. I was having trouble getting a good reading on the coast side. I thinned out the paint and it seemed to help a little, but that’s the best I could get.
Did you use an axle to turn this? From the looks of the sharp line at the root of the coast pattern it looks like the pinion is way too deep, but the pattern is very hard to read. Spin it several times with an axle and see if it gets more clear.
I put bolt axles in and spun it slowly from the pinion with a drill. I can’t spin it with an axle because it’s a torsen. It looks like the coast side is wide and towards the top of the tooth.
OK. I see it a little better now. Add about .010 to the pinion shim and try again. Don't use as much marking compound. Only mark 3 teeth and see how it looks.
OK. I see it a little better now. Add about .010 to the pinion shim and try again. Don't use as much marking compound. Only mark 3 teeth and see how it looks.
Ok I added a .010 shim to the pinion, but now my backlash tightened up to .003. I’m gonna the shim the carrier tonight and post the new pattern. Thanks
Also I’m setting this up with a used pinion bearing, as it’s much easier to press on and off. I have a new one going in when it’s all setup, not sure how much that will affect pinion depth. I know I’ll have to adjust the preload a bit.
There is still too much compound on the gear, or maybe you are not turning it enough times, but it does look much better. Try it with the new bearing and see how it looks.
The drive side wiped off clean and neat, but the coast side is still smeared and hard to read. It looks pretty good from what I can tell, but I'd like to see the coast side again after turning it several more times with pressure on it. Also, set the backlash to .007 if you can and see if it improves. If this is a 2 cut gear then .008 is way too much backlash. You need to find out if this is a 2 cut or a 5 cut gear.
Ok gears are 5 cut for sure. If I run a flathead along the root of the tooth it tapers down towards the heel. Unfortunately I don’t have the right shims to drop the backlash from .008 to .007. Here’s the best pattern I could get for the coast. You can tell by the root that I had the whole tooth covered before hand. I spun for a few minutes while putting a drag on the carrier with my other hand.
The thing to understand about shimming is, that you are NOT shimming "the gears"; you are actually shimming THE HOUSING. Gears are VERY consistent (especially within a single mfr, such as dealing with nothing but stock gears... changing from one mfr to another, not so much, always) Think of the correct setup as, the nice consistent all-the-same gears hanging freely in space, all meshing just right; and a random housing with highly variable machine work, draped around them, with just the right shims to even out the variation in the HOUSING.
GM did however get the pinion bearing bore machined very consistently in this particular model of rear. 99.999% of them come from the factory with a .035" pinion shim. There might be 1 or 2 somewhere with something else, but EVERY SINGLE ONE I have ever torn down, without exception, had a .035". Therefore when I build one, I always just slap a new .035" in it, to start. I have yet to need to change it, except with the Richmond drag race gears. Since you have good used stock gears, this would apply to those as well. That shim shouldn't be more than a .001" or 2 away from .035", and more likely in the direction of being slightly thicker than any thinner. If it's let's say .035" - .037" you're almost certainly within the correct range. And, since shims go with the HOUSING not the GEARS, that means you can virtually always take a housing, retain whatever pinion shim thickness it came with, and put the same on either other used or new gears (again, as long as the gears are of like kind), and it'll be fine.
For setup, I use a new (NOT used) pinion bearing that I honed the bore out with a brake cyl hone, enough to be able to install and remove easily; then press on the brand-new one for final assembly.
Also, what is the pinion preload set to? My personal preference with new bearings is to set it to the high side of the spec; 22 - 25 in-lbs or so.
Then, the backlash doesn't really affect the noise or any of that, within reason. "Spec" is something like .006" - .012". I like to set mine toward the tight side of that range, but not TOO tight. What you have is about what I usually use. The reason is, gears GROW when they heat up, meaning, backlash goes away, particularly under heavy usage; and I'd rather have just a hair of play in them when cold, rather than 2 pieces of metal trying to occupy the same volume just at the most critical moments in their life (long-term high load), which as we all know, never has a happy ending.
Carrier bearings should have preload, just like the pinion ones. Once you get the right shims picked out for the backlash, thicken them both by at least .005"; add as much as you can, equally to both sides, and still be able to get the thing to install. I don't have a case spreader (someday I'll make one maybe) so I use 2 large C-clamps on the carrier bearing outer races to preload them while assembling.
I'm not a big fan of using the pattern to set up gears, in a stock-ish situation. Especially with used gears. IMO it's overkill in terms of effort vs useful info provided, ambiguous, and otherwise just more trouble than it's worth.
Ok I got the rear back in, took it for a drive and noticed a bit of whine coming to a stop. Took it on the highway, it’s more of a slight howl, not very loud and only during light coasting when the diff is least loaded. Goes away almost completely when under hard decel, I hear it a bit when coming to a stop in gear or neutral. Should I try tightening up the backlash or just run it as it is? Pinion preload was at 20 inch pounds. I never have a quiet rear after doing poly bushings in the back, so it really doesn’t sound any louder than normal for me. Let me know what you think, thanks.
08-27-2018, 04:13 PM
