Installing a Zexel Torsen Differential Carrier in #29

From the first day on the road, driving STALKERV6 #29 has been a constant revelation of the performance potential of the little car. I learned very early that the car's road savvy far exceeded my ability to utilize all the car can offer. The combination of abundant torque in a 1500 lb car, while certainly exhilarating, also pointed out the short-comings of the S-10 open differential that is the standard donor part in the project. Dennis Brunton, STALKERV6 designer and kit manufacturer, told me when I received the kit that I would probably want to upgrade the open diff to a posi-trac type carrier. While the open diff is certainly adequate for general street driving, the V6's torque easily results in one rear wheel generating lots of smoke and less than optimal acceleration when the go pedal is mashed to the floor.

After 5000 miles of road use, I decided to execute the upgrade to the limited-slip differential (LSD). There are several LSD carriers that can be accommodated by the S-10 axle, but the most desirable OEM unit is the Zexel Torsen commonly found in the late-90's Camaro. This is a swap that is well-known in S-10 circles and can be accomplished by any Stalker builder. As of this writing, used Torsen's are readily available and even after replacing the carrier bearings, the swap can usually be completed for less than $250. Here are the specs on the Torsen unit that is compatible with our S-10 rear ends:

Zexel Torsen series 3, 7.5", 10 bolt, 28 splines

The swap would certainly be easiest if done with the axle off the vehicle and sitting on sawhorses. This is the preferred method for Stalker builders. However, I decided to attempt the swap with the axle in the car, knowing I could remove the axle if absolutely necessary. It turns out that by removing the fuel tank and some body panels, I had very good access to the diff and it was unnecessary to open the brake lines. The panhard rod was disconnected on the left end and tied to the roll bar. After removing the rear wheels and brake drums, loosening the diff cover and draining the oil, I was ready to get dirty.

Here are the two carriers on the workbench. The Torsen is on top with the standard open diff below. Basically, the swap involves removing the axles, persuading the old diff to vacate the diff housing, transferring the ring gear, and popping the Torsen into the housing. Replacing the bearings is a good idea while the carrier is out of the car. I took the Torsen and fresh bearings to a local transmission shop and they pulled the old bearings and pressed on the new ones for a minimal fee.

An explanation of how different types of differentials operate can be quite complex and beyond the scope of this article and its author! The Torsen is considered to be "torque sensing" and is different from a locker or true limited slip differential. Regardless of the semantics, the Torsen is a fine option for our Stalkers and has been proven in road and track use.

For more info on the Zexel Torsen, go to the Torsen FAQ page.

A very complete description of the Torsen installation process has been floating around the internet for quite some time. I have provided the text of the article below and have inserted photos of my installation as appropriate. I can only attribute the article to "BlueSkyJack"; whoever you are, thanks for taking the time to assist us with the installation!

========================

Before you attempt doing this yourself, you need to read and decide if you are equipped, capable and willing. If not, you’ll save time, sweat and heartache if you pay a competent rear end professional to handle it. On the other hand, doing it yourself is the only way to really learn how.

Much of this information is applicable to differentials in general, but most is specific to the installation of the Zexel-Torsen limited slip carrier into GM 7.5” or 7.625” rear differentials with 3.23 or numerically higher gears and 28 spline axles. Most ’89 and up GM models have 28 spline axles. However GM did use a few leftover 26 spline axles after ’89, mostly in 2.2s and 2.8s. If your vehicle is near the ’89 changeover date check to be sure. If you have 26 spline axles you can purchase a set of 28 spline axles and still do the install.

Ok, are you ready to get sweat, greasy and possibly frustrated while installing your Zexel limited slip carrier, AKA Posi-Traction?

If so, loosen the 13mm-1/2” cover bolts and drain the gear oil into a suitable container. Jack or lift the rear end after loosening the rear wheel lug nuts. Securely support the vehicle as high as you can on appropriate jack stands. Remove the rear wheels. Remove the brake drums by tapping firmly around the rear edge while pulling outward.

Remove the differential cover and rotate the carrier until you have access to remove the 10mm-5/16” pinion shaft retaining bolt [A] (use a 6 point socket to avoid rounding it off). You can now remove the pinion shaft [B] that slides between the ends of the axles and keeps them from moving inward. Gently push one axle in to remove the large C-clip that secures the axle from moving outward. Carefully slide the axle out of the axle tube so as not to damage the outer axle bearing. Use a clean rag to wipe excess oil off as you withdraw it. Push in the other axle to remove it’s C-clip and carefully slide it out.

Since you have the axles out, go ahead and replace the axle oil seals located at the end of each axle tube. These seals are inexpensive and may start leaking as mileage increases. It’s easier to pull the seals out with a seal removal tool, but you can use the tip end of the axle. Be careful not to damage the bearings or sealing surfaces on the ends of the axle tubes. You’ll get a bit more differential fluid draining out of the axle tubes when you remove these seals. Be sure to collect it in your drain pan. If you have high mileage you should consider replacing the axle bearings also. You’ll need a slide hammer and a bearing removal tool that is able to pull from behind the seal. You may need to obtain the axle housing code to get the correct P/N seals and bearings. The axle housing code is stamped on the front of the passenger side axle tube, between the pumpkin and brake backing plate. Insert new seals and fully seat them by pounding them in flush with a large socket.

Ok! Back to the carrier removal. On each side of the carrier there is a main end cap secured over the carrier bearing races by two 16mm bolts. Mark the caps so they can be returned to their original location. Remove and set aside the four bolts and end caps. The carrier can now be removed from the differential housing, but first examine either end of the carrier and you will see shims wedged between the bearing races and differential housing. They are used to pre-load the carrier bearings and adjust the position of the ring gear for proper backlash.

Keep an eye on the shims when you pull the carrier out so you’ll be able to relocate them in their original locations. You will use these shims or new ones close to the same thickness as a starting point for proper backlash adjustment. If your rear end is in reasonably good shape, and you are just swapping in the Zexel carrier and using your old gears, you may get lucky and backlash will remain within the specification limits of .006” - .010”, but don’t count on it. That’s why you bought an install kit complete with varying thickness shims.

You’ll need a pry bar or bars and block of wood to coax the carrier out of the differential housing. You can use the 3lb. dead blow hammer or sledge to bang the carrier housing while you pry to get it started. Be careful not to damage the gasket-sealing surface of the differential housing or the ring gear. The bearing races, tapered metal rings that cover the carrier bearings, may fall off as the carrier comes out. They set over the bearings on either end of the carrier and are held in place when the carrier is installed and shimmed. You’re going to replace both of these inexpensive bearing races with new ones. Consider it cheap insurance to protect the like new bearings which are already pressed into both ends of the Zexel unit.

To transfer the ring gear YOU WILL NEED TO USE A BENCH VICE to hold it while you remove the 19mm-3/4" bolts that secure it to the OEM carrier. (*IMPORTANT NOTE: THESE BOLTS ARE REVERSE THREAD.) Cushion the carrier with a thick towel while mounting in the vice. If you haven’t removed the rectangular pinion block from the middle of the Zexel unit, do so now. This metal slab will slide in between the ends of the axles to keep them pushed out the same way the large cylindrical pinion shaft in the old carrier did. (NOTE: If you are running larger than 3.42 ring and pinion gears you may have to machine or file a couple grooves in the pinion block to slide it past the ring gear teeth later in the install procedure). Be sure to clean the ring gear and all bolts before installing it on the Zexel carrier. If the bolts are in good condition you can reuse them or use new high quality bolts. The old OEM bolts are better than cheap after market ones. Mount the Zexel into the vice and transfer the ring gear. Install the REVERSE THREAD 19mm bolts using Locktite and torque to 90ft.lbs. Torque the bolts in a couple stages while moving across and around the ring gear in a star pattern.

Now with the carrier out it’s time to thoroughly clean the differential housing. Remove gasket material from the sealing surface and wash out the housing with clean solvent. Check all of the oil passages and grooves to make certain that there are no metal particles or dirt remaining.

You’re now ready to install the Zexel carrier into the clean differential housing. Apply clean gear oil to both carrier bearings. You don’t need to pack them with grease. Position the carrier with the new bearing races in place and shim the left side first. While holding the assembly in place shim the right side (an assistant will make it easier).

Clean and re-install the two carrier end caps in their original location over the bearing races. Torque the 16mm bolts to 50-60ft.lbs. Use Locktite on all bolts in final assembly.

Now carefully slide the axles back in taking care not to damage the lips of the seal and insert the C-clip into the retaining groove. Pull the axle back out to seat the C-clip in the counter-bore of the side gear. Clean and insert the rectangular pinion block between the ends of the axles. Tap it in lightly to seat it, don’t force it. If it resist insertion pull the axles outward while rotating slightly back and forth to be sure they are seated correctly. Locktite and torque the retaining bolt. Rotate the drive shaft to make sure everything is meshed correctly and the assembly rotates smoothly.

Apply a thin bead of gasket sealing compound around the cover and position the gasket onto it. Install the cover with gasket and torque the 13mm bolts to 10-15ft.lbs, again moving in a side to side sequence around the cover. Fill the differential with fresh gear oil to the bottom of the fill hole. Check for any leaks around the differential. Re-mount the brake drums and wheels, lower the vehicle and go for a test drive. Check the differential fluid level again on level ground after your test drive since some of the gear oil may have flowed back into the axle tubes. Congratulations, you now have two legs!

=========================

With a little luck, satisfactory gear lash and end-play will be maintained by reusing the original shims. If adjustment is necessary, here is the continuation of the above article that provides details on how to spec and adjust the gears and bearings.

Return to StalkerV6 Front page