10 Bolt Gear Swap (f-body)

10 Bolt Gear Swap (4th Gen F-body)

I wrote this how-to as a guide to help anyone through this process. I am performing the install on a 1993 Firebird Formula, and while all 4th gen f-bodies came equipped with GM’s 10 bolt rear end, there are a few changes from year to year (mostly in the differential itself). Before performing this install it would be wise to see what kind of differential is in your car, some of the zexel-torsen rears in some LS1 cars require modification to get certain gears to fit. There are many gear choices available, researching on forums will help you decide which is best for you.

If you are very mechanically inclined & experienced, have a decent set of tools and a day to spare, by all means give a gear swap a try. Hopefully this how-to will allow you to gauge whether this is something you can tackle or not.

To perform this install you will find it is handy to have air tools, especially an impact gun which you will use to remove & install the pinion nut. Since I did this car at my place of employment, I have access to bearing puller/removers that make life much easier…they are available to purchase, or you can try other methods of removal (such as heating/beating/etc). Most of the tools I used at the shop were made by Miller. I am not sure where to buy them directly. Some of the things you’ll need include a basic set of 1/2″ drive sockets & driver, 3/8th” driver (for removing gear oil plug), impact gun, pen magnet, dial caliper (for measuring shims), gear paint, 1 1/4″ impact socket, 18mm wrench, 11mm wrench, 8mm wrench, big pry bar, dial indicator gauge, chisel/punch, hammer (couple different sizes), and a couple odd things I’m forgetting.

You have a choice whether you wish to replace all of the bearings, or reuse yours. I highly recommend replacing everything since you will have most of it apart anyway. When you purchase gears there is often an option of purchasing an ‘install kit’ for another $90 or so, do it.

The absolute bare necessities include gear oil (75w90 for this car), shim kit, gear oil additive (for limited slip cars), loctite, and RTV gasket maker. If you are replacing everything, you will additionally need: carrier bearings (2), front pinion bearing, rear pinion bearing (all bearings will come with races), crush sleeve, and a pinion nut. You can also do wheelbearings since you will have the axles out.

Torsen differentials – see note at bottom

Traction control cars – see note at bottom

1. First you must get the car in the air. This install is much friendlier on a lift, but it can be done on the ground. When the car is fully in the air, put it into neutral and release the emergency brake.

2. Remove both rear wheels, set aside. At this point we also must remove the rotors & calipers, so that later we may remove the axles. Take the caliper & hanger off as one piece, by removing two 15mm bolts on the backside. Hang it from a bungee cord as to not stress the brake lines. Then slide the rotors off…if they do not come off easily, give the center a few pops with the hammer (between the lugnuts in a few different places). Now your axles are in plain view.

3. To make this installation easier, remove the panhard rod, which is a 21mm bolt and 18mm nut. If your car is on a lift you can just undo one side and push the rod out of the way…if it is on the ground you’ll need to remove it from both sides.

4. Now that the housing is unobstructed, remove the 13mm bolts that hold on the cover. When you get to the last bolt, remove it only halfway and pry open the cover until the oil comes out. Once you crack it open remove the last bolt and pull off the cover…just keeps you from flinging off the cover accidentally and making a mess. You may notice the magnet on the inside of the cover looking a little fuzzy, it is normal – just material from the clutches in the limited slip. Scrape any extra gasket/RTV off of it, clean it, and set it aside.

5. With the cover off, we can tackle the axles (I just thought that sounded neat). Turn the drive shaft until you see a small bolt facing the right wheel, it is 8mm. Put your wrench on it and give it a tap with the hammer to break it loose. Remove the bolt. The pin itself may slide out easily, it may not. If it does not, spin the drive shaft until you are looking at the opposite side of the pin. Tap it with a punch lightly, until it moves a half inch or so. Rotate the drive shaft back. Now the hole in the pin will be sticking out, and you can pry out the pin with a screwdriver.When the pin comes out, take care when turning the drive shaft. If you do not have a limited slip differential, the spider gears may walk right out of the carrier (not the end of the world, but frustrating to reinstall).

6. With the pin out, the axles are now free to be removed. With your hand, press the axle (at the lug nuts) inward, towards the center of the car. It will move half an inch or so, and you’ll see a c-clip hanging on the end. You can grab that with your pen magnet. Once the c-clip is removed, the axle will slide right out. It is slippery so don’t drop it! Repeat on the other side. Afterwards if you want to be safe, reinstall the pin & bolt to retain the gears within the carrier.

7. Now you can remove the differential itself. The main caps are 5/8″ (~16mm). Loosen them halfway, so that the cap moves but the bolts are still threaded solid. More often than not the differential will take some coaxing to remove, coaxing with a pry bar, that is. With your big pry bar the differential forward. It will pop out and rest against the caps, which you didn’t remove all the way because you didn’t care to drop a differential on your foot. From there you can remove each cap, keeping a hand on the diff. When the caps are off, pull the differential out. Know which cap came off which side!

8. When you set the differential aside and go back to the housing, you will see a shim on each side resting within, take those out…they may have come out when you remove the differential. Remember what side those went on as well, and remember that the chamfered side faces outward.

9. It is now time to swap ring gears, and bearings. On each side of the carrier you will have a bearing that is seated on the carrier, and its race, which probably clinked to the floor when you took out the carrier. Using a bearing puller, remove both bearings, and install the new ones. For re-installation I really like the tool that looks like a cylinder, hollow with one end open. You must select a size that sits on the inner bearing and does not touch the outer cage. These installers make seating very easy. With a large hammer, start beating the bearing on, slowly at first to make sure it is even. You will know when the bearing is fully on because the pitch of the hitting sound will change (it will start to hurt your ears), and your hammer will pop right back at you.

10. You can set the bearing races aside, they are not needed yet, because it’s ring gear time. The ring gear bolts are 16mm, and they are left-hand thread. Let me repeat that, they are LEFT hand thread. When you have all of the bolts out you will notice the ring gear is still stuck. You can do one of two things…reinsert 4 bolts opposite each other, half way. Hit the bolts equally in a pattern until the ring gear is dislodged…or, install two bolts halfway, and using a punch, hit the ring gear through the bolt holes until it falls.

11. When you install your new ring gear, it doesn’t hurt to use new bolts, for the old ones may have stretched. I also like to use loctite for good measure. Install the bolts in a star pattern, bringing the gear up evenly. When it is seated, do a final torquing to 90 ft/lbs (or a good hit with the impact gun). The carrier is now ready for installation, but we still have more to do.

12. Now we can remove the pinion, and set to work on it. Before that comes out, the drive shaft must be removed…it is held on by 4 11mm bolts. Mark the drive shaft and yoke so that you reinstall them the same way. When you remove the bolts the drive shaft should be able to move forward a bit (if not, pry it lightly). It will pop out. If the car is level and you remove the drive shaft from the trans, little fluid should spill. You can always let it dangle, but it only gets in the way…you already have enough in the way with the exhaust & torque arm.

13. Turn the pinion yoke by hand, to feel what it is like. Also take note of roughly how far the pinion comes through the pinion nut. With your impact gun and 1 1/4″ socket, remove the nut. You can hold the yoke with your hand, just use a lower setting on the gun as not to mangle your fingers. When the nut is off, remove the washer behind it and set it aside. The yoke should pull off easily, and then the pinion will slide out the back.

14. Now you can remove the pinion seal, whether you pry it off or hit it from the rear. I usually take my big pry bar and pop it out really quickly. Behind the seal will be a bearing, remove that as well. Now everything has been evacuated from the rear except the front & rear pinion bearing races.

15. You can remove the races a couple different ways. There are tools made for them, but I couldn’t locate it. The next best thing is a long punch, or a long 1/2″ drive extension. If you view the race from the rear, you will see two notches in the housing where you can beat the race from behind. Place your extension there and beat the shit out of it, going from side to side. It needs a good beating to get out of there so don’t be shy. The rear race is removed from the front, and the front race is removed from the rear (any order).

Looking from the rear, you can see where you will hit the front bearing to remove it. Looking from the front, you will be able to see the notches where you will force the rear race out.

16. Now you may want to clean the inner housing a bit with some brake clean, to ensure nothing will get stuck between the new races and the housing. Installing new races will be a LOT easier if you have a set of tapered installers…you will need to find one that sits around the edge of the race, but does not touch the inside of it. I hold the race in the housing, seat the installer, hit it a couple of times to seat it…check to see that it is going in evenly, and then whack away. You’ll know it’s fully seated when your hammer bounces back at you, and when the noise is almost too much for your ears to bear (it’ll get higher pitched once again). Install both new races, and head back to your pinion.

17. Even if you are using new pinion bearings, you still need to remove the old bearing from the old pinion so that you may retrieve the shim from underneath.

17a. In every rear end I have ever done, I have used the same old pinion shim with success. I am sure there are cases which dictate otherwise, but I have not encountered it. Should you get into a situation where you need to fool around with pinion shim size, you can cut the old bearing in such a way that makes it easy to remove & install, while you ‘mock’ up your rear end to check backlash & pinion depth. I used a puller once again to pop the bearing off easily…clean off the shim, slide it onto the new pinion, and install the new pinion bearing…once again I used the tube style installer. Before you put the bearing on, make sure you are using the correct size installer…if it is too small, it’ll be difficult to remove from the pinion, and if its too large, it’ll destroy the outer cage of the bearing.

18. Once your pinion is ready with the new bearing, slide the new crush sleeve on.

19. From the rear, slide the pinion in. Have a friend press firmly against the pinion while you seat the front bearing, with an installer or a punch. It’s not completely necessary, but makes installing the pinion nut go a little smoother. Once the bearing is on, now you can install your new pinion seal (your f-body thanks you). Tap it lightly to seat it evenly, go slow and use a rubber mallet or a block of wood underneath your hammer so as to not ding up the seal.

20. As of now, precision is going to be important, because you are dictating how your rear end is going to mesh together. Take a scotch brite pad and briefly clean up the area of the yoke which slides onto the pinion. Place it onto the pinion, and don’t forget the washer! Place some loctite on the new nut (or the pinion threads) and thread it on until it won’t move anymore (it is a locking nut so it won’t go too far). Wrap a rag around your hand, hold the yoke, and with your impact gun on medium or low, begin to tighten the nut. It will seem like it takes forever. When it is fully tightened, there will be no slop when you attempt to pull back and forth on the yoke.

21. Give the pinion a spin with your hand…is it similar to what you started with? If not, tighten it more. There is a tool available for an exact measurement of drag, if you want to be specific, pinion bearing preload needs 24-32 inch/lbs tq, or 8-12 inch/lbs if reusing your old stuff. To be honest though I have done quite a few rear ends and usually perform this measurement by feel. (So do as I say with the tool, not as I do with my hand). Using the tool on an f-body is a pain anyway because the torque arm and exhaust don’t allow any room at all to move it.

22. Now that you have installed the pinion, you can reinstall the differential. Pick up the differential and slide the races over the bearings on either side. Hold one shim on the edge of the race, and insert the differential into the rear end. Place one main cap over the side you chose to put the shim on, and thread the nuts by hand. On the other side, push the race back onto the bearing, insert the shim as best as you can, and GENTLY tap it in with a hammer until it is fully seated. When everything is in correctly, tighten down the bearing caps to 65 ft/lbs.

23. With that finished, you can now check backlash. Backlash is how far away your ring gear is from the pinion. Too much or too little are both bad things…we are shooting for .006″ (Richmond gears call for .006″, Motives say .008″-.0012″) which we will measure with the dial indicator gauge. When you grab the ring gear with your hand, move it back and forth. You will not be moving the ring gear as to actually turn the pinion, rather just shift it back and forth to feel the play. You’ll understand this further when you actually try it. Attach your dial indicator gauge to the rear end housing, and set the indicator so it is touching the ring gear. Shift the ring gear back and forth again, and see how much you end up with. Measure backlash in a few different areas. If your stock shims worked out and you got .006″, thank your lucky stars, you rock!

24. In my case, the backlash only amounted to .002″ – .003″, which means the ring gear was too close to the pinion. I removed the differential again and measured the shims. The right shim was a few thousandths less than the left when I measured it with the dial caliper, so I switched the shims. If you think about what is happening, it makes sense. Less shim thickness on the left side moves the ring gear away from the pinion, and when I remeasured, I got .006″ right on the nose. Depending on your situation, you will have to use the right amount of shims to move your ring closer or further from the pinion. This can be a little time consuming, so if you are feeling frustrated take a break.

25. Now you will want to take a look at how the pinion and ring are mating. get some gear paint from the store, and slather it on a few teeth on the ring gear. Rotate the pinion gear through the marking compound once in each direction (drive and coast). In this step you are basically verifying that you set the rear end up correctly. You might need to rest your hand lightly on the ring while you turn the pinion (to add some drag to get the pattern to show up). You are aiming for the pattern to be about one-half the length of the gear tooth, in the center. I didn’t have any gear paint to do this with, so I used white lithium grease, which didn’t show too well in the photos.

26. When I am satisfied with the pinion, I take a punch and put a few ‘pings’ in the pinion nut, to ensure that it will not move. If you look closely at the nut you’ll see it has little notches in it just for this purpose. Once your rear end is set up correctly, you can begin putting it back together. Remove the pin that holds the axles in again…slide each axle in as far as it will travel, insert the c-clip, and gently push it towards the outside of the car. When both axles have been installed, reinstall that pin as well, giving the wrench a few final taps with the hammer to snug it.

27. With the axles on, you can reinstall your brakes. Slide the rotor on, mount the caliper/hanger onto it, re-secure the hanger with the 15mm bolts. Put the wheels on and tighten the lug nuts. You can also reinstall the drive shaft, use a dab of loctite on the bolts when you tighten them.

28. Apply some RTV around the cover & boltholes, and reinstall onto the housing, tightening the bolts in a star pattern to 20 ft/lbs. Some people like to use paper gaskets for the rear, I don’t. It’s your choice, I like RTV because it never leaks. With your 3/8th” drive ratchet, remove the plug in the housing where you will refill the rear end.

29. Add your rear end fluids…this car used 2 quarts of 75w90 oil, and a bottle of GM’s limited slip additive. Reinstall your panhard rod, with the 21mm nut and 18mm bolt…now stand back and admire your work – you’re done!

30. It is not a bad idea to test drive the car gingerly at first, listening for noises or other potential problems (we all do stupid things now and then). Follow the gear manufacturer’s instructions for break-ins, and enjoy!

appendix – I recently installed a 4.10 gear into my ’00 LS1, which has a torsen rear end. I used motive gears and did not need a paddle kit, however I have heard that with certain gearsets you will need to use a kit, or grind down the paddle. Basically the new ring gear is too thick to slide the paddle back in (the paddle is what the torsen uses to keep the axles in instead of an axle pin). You have four choices…you can buy SLP’s paddle kit ($160) you can grind the rear corner of the paddle to get it in, you can beat the paddle in, and you can grind down the ring gear teeth (I do NOT recommend that). If you try and beat the paddle in you may be successful, but how will you remove it again should you have a problem? I think the first two options are the best. You can always buy the paddle kit, keep your receipt. Use it if you need it and if not, return it.

Traction control cars – you need to remove the rear sensors from the backing plate in order to get another 1/8th” to push the axles inward (to remove the c-clips). It is one 10mm bolt.



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