Chevy & GMC Vans

I'm going to have the front end all apart soon, so I wanted to get the s10 front diff I have, setup and ready for install.

I've never done gears before and since I can do this "on the bench", and with encouragement from Lifted, I thought I'd give it a try. That said, any advice from oh great knowledgeable ones is encouraged!

Opening the halves was simple enough, just a bunch of bolts. The pinion nut required a 32mm socket ($4.50 HF). I used a pipe wrench to hold the ujoint yoke an impact wrench to loosen the nut. With the nut halfway threaded on the pinion, I tapped the pinion free of the outer bearing (you will want to keep that nut for future tapping).

I am installing a used gear set, and the existing bearings (95K miles) look and feel good. So I purchased a "mini install kit" from Yukon. This kit comes with a new seal, crush sleeve, pinion nut, shims and contact marking compound.

Next I had to get the inner bearing off the pinion. This was a bit of a bear as I didn't have a separator; I used two pieces of 1/4" steel and my vise. Fortunately the Yukon kit shims go behind the outer race rather than the inner, so I only had to remove that bearing once. Here's the original OEM shim on the pinion after removing the bearing The outer race of the inner bearing can be remove with a soft punch. I used a soft carriage bolt, not ideal but it's what I had. Here's a pic of the case with the outer race removed. The new shims go in the bore. I'm thinking the only special tool I need is this dial indicator with magnetic stand ($26 HF) Since I don't have a micrometer, I set up the DI on the flat of my vise and used it to measure the original pinion shim - .0038 I then picked a new shim pack that closely matched - .0039 I used the pinion assembly to press the race back in the housing: ok, I know there's got to be some cringing out there! It didn't take much force so I'm hoping the bearings aren't compromised. I cut the locking swedge off another old pinion nut so that I would have a "clean" low friction nut to use for the many test-assemblies.

here is the test assembly nut. It made the multiple assemblies easier and didn't stress the pinion threads. Next was adjusting the pinion pre=load. I don't have a in/lb torque wrench, so I used this fish scale instead; I used the same scale before disassembling the orignal setup so I had a base line measurement. It so happens that the 5# measured at 1.25" also falls within the 6-7 inch/lb range suggested for the PL on the used bearings!

I bolted the new ring gear to the carrier using new bolts as recommended. Then assembled the entire case (using only four bolts) to measure the backlash. The BL is a bit tricky to measure on these due to the fact that you can't get to the ring gear to measure it (it requires a special tool). So I came up with the following plan: since the measurement is supposed to be taken at the outer edge of the ring gear, the same measurement could be made at the outer edge of the pinion where the two gears mesh. I took that measurement from centerline and projected it to a point on the face of the pinion flange that I could access with the dial indicator. Using the carrier preload adjusters I adjusted the backlash to .0010 (range .0006-.0010) I ended up using a drift punch to adjust these.

after the backlash was set, I pulled the case apart and put some marking compound on the ring gear and re-assembled. Then turned the ring gear as suggested (not the pinion for some reason) about 4 revolutions in each direction. Then take it a part and check the pattern. Since I had both hands on the axles I couldn't put much resistance on the pinion, so I think my pattern is kind of hard to see

coast pattern
drive pattern They don't have the nice oval contact pattern of new gears, but apparently that is not uncommon for used sets. Also the drive side is a little heavy toward the toe, but I guess that's normal also. Anybody have any comments about the pattern?

Very good write up. I do not have experience with gear sets but I sure learned from your photos and text. Thank you for posting. I have 3.42 gears on my 2003 AWD Astro. Some day would like 3.73 or 4.10. I get 16.5 mpg on highway with 225/70-16 BFG TA KO tires. I have 2 " lift.

Astrophysics

I have 3.42 and was going to go with 3.73's as that is what came in the donor s10 axle. Lifted highly recommended the 4.10's. Between the better matched gears and the axle disconnect, I'm hoping for improved mpg as well. At a minimum the 4.10's should help get the 31" tires up the 3,000 foot vertical grade between here and town!

Doesn't look too bad but spin it over using the pinion a bunch of times and see if you can get a better look at the pattern. I also like to look at the pattern on the teeth you didn't put marking compound on. Sometimes you can see them better.

What shim was under the 3.42 pinion and what shim was under the 4.10 pinion?

When you adjusted the carrier preload nuts did you move them both the same number of notches so that the overall separation distance stayed the same? This will keep the preload correct especially since you are re-using the bearings.

The original shim on the 3.72 was .0038. The 4.10 didn't have a bearing or shim so don't know about it. The Yukon kit came wit a lot of shims, but only two thicknesses: .0032 and .0010. I went with a total of .0042 ( .0032 + .0010) the closest I could get. (4= stacked .0010 measured closer to .0044).

RE the carrier adjusters- I loosened one a notch and tightened the other in the sequence you (and the manual) recommended.

I'm pretty happy with the pattern, though the drive side runs off the toe some.

I'll run the pattern some more using the pinion and take some more pics (for some reason some references suggest only turning the ring gear pattern?) The only thing that looks a little weird to me is that the coast side seems to be making contact only down toward the root. The other strange thing is that the contacts on both sides seem to wander a bit from heal to toe on different parts of the ring gear.

What you may want to do is pull the Yukon shims from under the race and install the 0.0038" shim under the bearing like the factory did. Then be 100% sure the races are fully seated before seeing up again. I am surprised the Yukon kit doesn't have many thin shims stuck together. Sometimes they are hard to get apart.

LiftedAWDAstro wrote: Sometimes they are hard to get apart.

Man, thanks for that! One of the .0011 was a .0005 and a .0006 stuck together!

Here's what it looks like still at .0042 in three different locations: Left is drive - Right coast

From the pics, it looks like you could add some shim to the pinion to move it towards the centerline of the carrier. It appears that the contact pattern is more towards the face rather than centered between the face and flank. You want it centered as much as you can. Then adjust the backlash per spec. Nice thing about the front diff is that it isn't driven all the time so being slightly off won't affect operation like a rear axle setup does.

thanks Dean. My biggest concern is noise, as I have it in awd much of the winter.
This really wasn't very difficult (yet), is the rear any harder? The only thing that scares me about the rear is the carrier shimming!

Yeah the rear is harder but only because of either doing in the van or removing the axle. The carrier shimming is a little bit of a pain but it's not too bad.

Good info! I may do my own 4.10 gears down the road, 3.73 now but with 31" tires I'd prefer the new gearing.

Go photo, Go Photo... I'm psyched to see you trying this. You're getting great assistance and building my courage as well! Kelly

I finally had some time to put this back together. Without getting into the details to much (it's all pretty simple and explained in the nice pictured instruction manual that comes with the Yukon install kit), here it is.

Once you have the contact pattern the way you want it, you need to get the final pinion preload adjustment with the new crush sleeve and pinion nut. What they don't tell you is that it takes 400-500 ft/lbs to compress the crush sleeve. For those of you that don't have a calculator handy, that's 100lbs applied to the end of a 4ft leaver! Or a hefty impact wrench. My HF air impact was definitely not up for the job, and even if it was, I would have had to been VERY careful with it. The preload on a used bearing set is suposed to be 6-7in/lb. Once the crush sleeve begins to crush and the bearings come into contact with one another, the pre load comes on VERY FAST! If you exceed the preload significantly, you need to take it all apart and get a new crush sleeve.

In order to apply 400+ ft/lb to the pinion nut, you need to keep the pinion flange from turning and hold the case in place. I bolted a piece of flat stock scrap to the flange and clamped it to the bench. I ended up not able to use both holes as the stock would interfere with the pinion socket Then I lagged the housing to the bench Lacking a braker bar that I felt suitable for a 4' cheater, I opted for a (cringe) pipe wrench. It took a good amount of my body weight at the end of this four foot pipe to start crushing the sleeve I actually found this part to require the most patience as I would only go 1/8 of a turn at a time, then disassemble the contraption and check the tightness, put it all back, try to get a "bite" on the socket again, then repeat. Definitely took some patience, but I got it.