whats with shimming the clutch pack in a traction loc?

Traction Loc

mfp4073 said:

I have several here in front of me...2 in peices and one that was together. The two that are apart have what I belive to be (and is called in a manual) a shim. Now my question is when to shim, why to shim and such. Also, back to gear lube, I was under the assumption that you used normal gear lube with an additive. Someone else has said, you can only use limited slip gear lube. Whats the answer there?

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You can run regular gear oil with additives. I run regular gear oil with trans-x from autozone. Just don't forget the additive. It'll chatter worse than any locker system nightmare you've ever heard

The shims determin how tight the limited slip is. The looser the clutch pack, the more it will have a tendinicy to deliver power to one tire. On the other hand, too tight and you might as well have bought a spool. Like all things automotive there is a spec for this.

mfp4073 said:

There is a figure in the hayes manual of 1500lbs but that seems exesive. Also it appears that one of mine never had a shim in it at all. Where do I test 1500lbs at? (as par normal...the book just says that and then says you should not mess with it.....)

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The 1500lbft is the "breakaway torque" of the diff, ie it'll start slipping a wheel. not really something you can measure. the ZF LSD (which I assume is similar to the trac loc) has a spec of "0-0.05 mm play cold"
Some people "preload" them by making it so that diff is locked up to an extent when you bolt down the cover, but this accelerates destruction of axles and the diff centre cover plate.... and also wears the plates faster. Best way to reassemble these clutch pack diffs is to oil the friction surfaces before assembly, They actually rely on a micron thick layer of oil being between the plates to prevent plate wear, while the extremly thin oil film transfers the drive..... exactly like a motorbikes multiplate "wet" clutch....

Ben

I had the limited slip in my '65 shimmed when I installed the 3.89 gears and it was not smart move. Sure the car went straight well, but it wouldn't make a decent U-turn on a bet, and wore out tires at a pretty quick rate.

I'm led to belive that the torque value can be calculated rather than measured also. When the centre is nearly assembled, a measurement is taken from the face of the last clutch plate to a machined surface on the housing (not exactly sure which one). Depending on the spring rate and the amount of shims used, this distance will equate to a specified torque value when the centre is assembled and the clutch plates are squeezed between the springs and the housing.

If you're getting excessive slip, the clutch plates may be worn out or just require shimming. Add shim = less slip. I have no idea on what thickness shim = limited slip value but i'm sure you local diff shop should have plenty of experience in this area.