Rear Gear Swaps

This is Craig's now-infamous guide to installing new rearend gears. It's from numerous e-mails to his 2QuickNovas cohort (Bruce) so if its seems to jump around a little, that's why.

Here's the basic procedure for a Salisbury rearend (most '60s and later rear-wheel-drive GM products):

1. This is best done with the body of the car on jack stands so that the rear end is dropped as low as it can go. Pull the rearend cover, drain the lube, and this is approximately what you should see:

Yours may or may not have that S-shaped spring in the middle, that indicates a limited-slip carrier.

Number the bearing caps so that you get them back on the same side from which they came. I used a punch and put one mark on one cap and a matching mark on that side of the housing, then punched two marks on the other cap and on the other side of the housing. If you look closely at the full-size version of the above picture you can just barely see the marks in the bearing caps.

2. Use a 5/16" wrench to remove the bolt that holds the cross pin in and then pull out the cross pin. This picture shows the bolt partially removed and you can see the end of the cross shaft:


This will let you push the axles in slightly (about a quarter-inch) and then remove the c-clips. A telescoping magnet works well. Here's the cross pin coming out:

3. Remove the axles from the housing, unbolt the carrier bearing caps and drop out the carrier (be careful, it's rather heavy). Keep track of the bearing races to make sure you put them back on the side they came from. Also keep track of what shims are on each side - it may change, but its nice to know in case you want to put your old gears back in sometime.

If the carrier is extremely hard to remove, you may have to put a box-end wrench on one of the ring gear bolts and then rotate the pinion gear. This should dislodge the carrier after the wrench contacts the housing. Be careful and don't let the carrier fall and damage you or itself. Thanks to Dan Hardison for this tip.

4. Unbolt the driveshaft from the yoke and remove the pinion nut and yoke. This will let the pinion come out the back side (from inside the housing), but you might have to tap the threaded end with a plastic or rubber mallet to dislodge it if it's stuck. If it requires more force than you can give it with a soft mallet, make sure nothing obvious is preventing it from coming out, then put the pinion nut partially back on to protect the threads and tap it lightly with a 2-pound mallet.

Here's a virtually empty rearend housing. A is where the left carrier shim sits, B is where the carrier bearing race sits, C is the rear (large) pinion bearing race, and D is the front pinion bearing still installed. It's retained by its race on its backside and by the pinion seal on its front side.

5. If you're replacing the pinion bearings, drive out the two pinion bearing races. The pinion seal and front bearing will come out with the front race if you wish to do it that way, or you can remove the pinion seal first, pull the bearing, and then drive out the race.

Now wash out the housing really well and drive in the new races if you've previously removed them. Be careful not to raise any burrs anywhere.

6. Take your old pinion gear to a machine shop and have the rear bearing pressed off, but be sure to save the shims under it. Put those shims on the new gear and have a new bearing pressed on since the old one will most likely be damaged by removing it. If you get a new bearing be sure to buy a new outer race, too, as they typically aren't sold together. If you lose your old pinion shims or something happens that you can't use them or measure how thick they are, use a new .031" shim to start out. It seems to work more often than not.

7. Unbolt the old ring gear (the carrier has LEFT handed threads for the ring gear bolts - don't forget!). Look at the carrier and the new ring gear for any burrs that won't let the ring gear seat flat on the carrier and file them off if there are any. Put on the gear and torque the bolts to what ever the instructions recommend. Loctite is recommended on these bolts but I've never had any trouble with them backing out.

8. Slide a NEW crush sleeve onto the pinion gear shaft and slide the pinion in the housing. Slip on the front bearing (making sure there's a front bearing race!), smear a little RTV on the outer diameter of the seal and drive it in. Then dab some blue 242 Loctite on the pinion gear threads and put on the yoke and nut, but don't torque the nut yet, just tighten it enough to take out the play in the pinion gear.

9. Snug up the pinion nut and using an inch-pound torque wrench, measure the amount of torque required to rotate the pinion gear. You are not trying to torque the nut with the in-lb torque wrench, you are just measuring how much torque it takes to turn the yoke and gear at a steady pace. Your gear instructions should give you a value to shoot for, but for used bearings it's probably about 10 in-lbs, for new bearings around 25 in-lbs. Tighten the pinion nut incrementally (takes a lot of force to crush that crush sleeve) until you reach this value of turning resistance. You can probably borrow the inch-pound torque wrench from a local mechanic since you won't have much need for one any other time and they're not cheap.

To clarify that step, you need to turn the pinion nut a little bit at a time and then check the torque require to turn the pinion gear and carrier. If it's too little, tighten the pinion nut a little more then check again. It's important to sneak up on this torque value slowly because if you go too far and get it too tight you have to remove the carrier and pinion gear, remove the crush sleeve, install a new one, and do it all over again.

10. Put the carrier back in the housing and take a guess at the side shims (I'd start with the stock shims on each side if you can get them in like that). Put the caps back on and torque them down. Put your dial-indicator so that it reads perpendicular to a ring gear tooth. You are shooting for about .008" back lash. Just lightly rotate the ring gear back and forth and measure the amount of slop (technical term!). You can feel the ring gear contact the pinion as you rock it slightly, then rock it back the other way and calculate the difference in dial indicator readings at each end of the free play. If there is too much backlash, move the ring gear closer to the pinion by adding shim thickness to the driver's side shim pack and taking an equivalent amount out of the passenger's side shim pack (you want the total overall shim thickness to be the same as before, you're just changing where that thickness is located). If the backlash is too little, do the opposite maneuver with the shims. Do this until the backlash is at whatever the gear manufacturer recommends.

11. Put some gear marking compound or white grease on the ring gear and rotate the pinion smoothly in the proper direction (so that the car would be going forward). Look at the pattern left in the grease. It should be centered and rectangular on the ring gear tooth. Your instructions should give you some good info on what your looking for.

12. If everything looks good, slide your axles back in, put in the c-clips, slide in the cross pin (making sure the side gears are in properly) and install the bolt that holds the cross pin in.

13. Now you're ready to put the cleaned cover back on and fill it with lube. If you have a posi carrier, be sure to use the posi additive, too.

14. Follow the gear manufacturer's break-in procedure.

15. Lay rubber!!

Additional notes and tips:
It's really not that big a job once you know that the trick is to start with the stock shims under the pinion bearing. The side shims are easy to change, but the ones under the pinion bearing are a pain in the butt. If everything goes well, you should have a quiet setup and the car will feel like it's picked up 100 hp!

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You will need to find some way of keeping the pinion from rotating while loosening and torquing the pinion nut. I found an old body spoon (I guess that's what it is!) that I wedged between two bolts in the yoke and let the other end rest on the floor. Since originally writing this, I have welded up a bar that bolts to the yoke and is long enough to rest against the ground or floor. It really makes torquing the pinion nut a lot easier.

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I was able to borrow a wide assortment of shims from the local GM dealership and then I just had to pay for what I used when I brought the box of shims back. I think they charged be 50 cents per shim. You may not need any shims either, so if you can spare the time it's nice to do the job and see what you need before you buy anything, but if you do it that way you'll be down for a while while you chase down the necessary parts.

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Generally it's not necessary to replace the carrier bearings if they were running quiet before, but if you do make sure you use new races. Don't put a new bearing on an old race.

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If you buy a posi carrier, make sure it matches whatever gear you'll be using. I used to have a posi unit from a Camaro that came from the factory with 2.41 gears so I had to add a ring gear spacer to use better gears. It hasn't been a problem yet, but I'd rather not have the spacer. FYI, the spacer is available through most drivetrain shops as well as through Jeg's and Summit for about $25.

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I bought the Ratech install kit, but it's basically just a few shims, a seal and a crush sleeve. You could probably buy them individually as cheap or cheaper. I'd check on finding a shim deal like I have here with the GM dealership where I borrow an assortment and use what I need, then pay for what I used when I bring the rest back.

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You can reuse your front bearing and race if they are in good shape. This bearing is a very light press fit and won't be damaged by removing the pinion from it. It will stay in place along with the front race as long as the front seal is in place. If you replace the front seal, just make sure you remove the bearing and keep it clean until you reinstall it behind the new seal.

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To do the basic job you might need side shims and you'll probably need a new front seal, a crush sleeve, gear lube and posi-additive. The basic installation kits don't come with much of a selection of shims, so you'd probably be money ahead to buy all the stuff separately unless the kit is really cheap and that's all it comes with. I can't remember exactly what came in my kit. I guess I'd check the prices on the stuff individually and compare that to the kit price.

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The carrier bearings are pressed onto the carrier and will be replaced when you put in the posi unit. I'd spin the bearings by hand and feel for any roughness. Carrier bearings last quite a long time. Usually it's your pinion bearings that start whining since they see a more of a cyclic loading.

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If you've got access to an impact wrench, things will go much easier for you. The pinion nut is self locking and the ring gear bolts are torqued pretty tight and it's hard to keep from turning the whole thing with a regular wrench. Go easy when installing that pinion nut though, it's easy to go too far, too fast with an impact wrench. Some say that an impact will put flat spots on the rollers of the pinion bearings, but I haven't seen evidence of it so far.

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Here's a tip on getting the pinion bearing races out: use a long punch and the biggest hammer you can swing with one hand. There's not very much room to swing it, so you need as much mass as you can get. You won't need to disturb the front bearing race to drive out the big race. I wasn't sure until I took my rear apart, but it's not a problem. I didn't even have to take out the front seal.

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The 25 in-lbs (with new pinion bearings) torque to turn the assembly is measured while turning only the yoke and pinion gear. Just try to turn the torque wrench at a steady pace so you aren't accelerating or decelerating it. It takes a lot more torque than that to tighten down the pinion nut. Its hard to do without an impact wrench. But you have to sneak up on it so that you don't over-compress the crush sleeve.

The best way I've found of torquing the pinion nut (except for an impact) is to bolt in a very strong shaft into one of the u-joint saddles using the u-joint strap and then torquing the pinion nut with a strong ratchet and a floor jack. A long cheater bar will just flex.

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Just a final note, the crush sleeve might be kind of hard to find unless you happen to know that a '88 (and probably many other years) Chevy pickup with the 8.5" 10-bolt uses the same crush sleeve as a 8.5 10-bolt that are in most of our beloved 70's Chevys. Your local GM dealership will have one. Bruce recently went into his local dealership and was successful when he requested "a crush sleeve for a '72 Nova with an 8.5" 10-bolt." Cost him about $5. Your luck may depend on your dealer and whether his info goes back far enough.

If you have any questions or comments please click the "Contact Craig" link and let him know.

Copyright 2008 Bruce Johnson and Craig Watson