Servicing 9-Bolt (Borg-Warner) Limited Slip Units

Experience with differentials is highly recommended. This procedure is not for the weak hearted. Hunter Motorsports assumes no liability whatsoever for anything resulting from anything, blah blah blah you get the idea. So here we go.

First you need to find shims. There is no G.M. part for this, you just have to use whatever is available.

DIMENSIONS FOR SHIMS:
Max Outside Diameter=2.5"
Min Inside diameter= 1.5"

You need a variety of thickness of shims ranging from .010" to .050" in .005" increments. Some types of differential pinion bearing shims will work for this purpose, but use whatever you can find.

Raise vehicle and support with jack stands on chassis of car. Let the axle hang all the way down, as it is much easier to work on. A hoist is very nice if you have access to one.

1. Remove differential cover.
2. Remove axles. -axles are retained by plates on the outside of the housing, brake hardware must be removed to allow removal of the axle shaft.
3. Remove differential carrier from housing. You may have to pry it out with a large pry-bar. It is VERY important that all shims and bearing caps be kept in order for re-assembly as everything MUST go back together exactly as it came apart.
4. Mount one axle in a LARGE bench vise with splined end pointing straight up. The vise must be securely mounted to a strong table or work bench.
5. Place the differential carrier over the splined end of the axle with the ring gear teeth facing downwards.
6. Mark the 2 halves of the housing for alignment during re-assembly.
7. Loosen the bolts that hold the housing together. (the ones with the 7/16" head) It is not necessary to remove the ring gear, however if it is to be removed it should be marked prior to disassembly for proper re-alignment.
8. Once all the bolts holding the housing together have been fully loosened remove the upper carrier housing from the assembly. All the internal parts for the differential are now accessible. Each half of the carrier houses a friction cone and a side gear. All parts must be kept in order. Place match marks on the cross shaft and spider gears prior to removal. There should also be a spring pack in the centre of the assembly, which should have 3 springs together. G.M. recommends replacing these springs anytime the differential is apart, but if they are not broken this should not be necessary. If any other parts are broken it is recommended to find a complete replacement for the carrier, however single parts such as side gears or spider gears may be replaced individually in emergency situations. If a friction cone is worn to the point where the end of the cone is contacting the housing at the inner most point (it will be evident by the wear pattern) then the carrier must be replaced.
9. Place the friction cone in its respective half of the housing and insert a shim between the side gear and the cone. Place the cross shaft with spider gears on top of the cone and gear in the housing. If the cross shaft seats fully into the housing and there is play between the spider gears and the side gear then use a larger shim. The idea is to remove all play in the gears while still allowing the cross shaft to seat fully in the housing. If too big a shim is used then the cross shaft will not seat properly and the assembly will bind causing the differential to act like a spool or possibly cause premature failure.

ADVANCED SETUP- SOFT FEEL shim each side until all play is removed and cross shaft seats properly in case, then remove .005 to .010 inch of shim.

ADVANCED SETUP- HARD FEEL shim each side until all play is removed and cross shaft seats properly in case and add up to BUT NO MORE THAN .005" of shim per side. This will provide additional preload to the differential that is not possible unless the gears themselves are loaded. Recommended for race use ONLY. If the vehicle is to be street driven on a regular basis it is not recommended to preload the gears.

The optimal amount of shim for Street-Race use is the point where all play is removed from the side gears and the cross shaft and spider gears seat properly in the housing. All one wheel peel will be eliminated and the differential will still operate normally.

RE-ASSEMBLY (This part is easier with 2 people)

1. Place components into case half without ring gear and place onto axle mounted in vise. It is important to re-assemble the case using the axles to align the internal components, otherwise the splines on the side gear and the friction cone may not be aligned and it will be impossible to insert the axle when the case is tightened.
2. Place cross shaft with spider gears into lower half of case and insert preload springs and spring plates.
3. Place other side gear on top of spider gears, then place the correct shim on top of the side gear then place the friction cone on top. All components should now be in place and in correct alignment. Double check to make sure there are no left over parts.
4. Place other case half over the assembly. Make sure the alignment marks line up.
5. Insert all bolts and hand tighten. The case may not seem to go together at this point, don’t worry, the preload springs have not been compressed yet.
6. Insert other axle shaft into upper case half and align friction cone and side gear. Do not remove axle shafts until carrier is re-torqued.
7. Tighten bolts little by little in a cross-pattern until the 2 case halves seat together then torque to 29 Lb.Ft.
8. Remove axle from upper case half (you may have to hammer it out) and remove carrier from axle mounted in vise.
9. Re-install carrier into housing making sure all parts are re-installed in original order. It will be a tight fit, one side bearing shim will have to be GENTLY tapped into place with a hammer, preferably a brass faced, or use a brass drift. Install all components except one side gear shim, then do the remaining side gear shim last and gently tap it into place.
10. Install bearing caps in original positions and torque to 40 Lb.Ft.
11. Install axles. They may need some persuasion with a hammer to fully seat. Tighten axle retainer bolts to 36 Lb.Ft. Don’t forget the calliper mounting plates or brake backing plates.
12. Install differential cover. Use silicone to seal cover to case. All parts must be clean and dry.
13. Re-fill differential with high quality gear lube, preferably synthetic. If a synthetic is used, the G.M. friction modifier additive should not be required. If a conventional oil is used the friction modifier may be needed to control chatter.
14. Install plug, lower car and ENJOY!