How do I check my ZF differential?
 

I'm beginning to wonder if my ZF LSD is functionign properly. Is there any way do do a basic check, say blocking a wheel and puttiong a torque wrench on the axle?

Should the car be in gear, what torque should I get?

Chris,

With one wheel blocked and the transmission in gear, use an indicating (not click) type torque wrench and turn the free wheel using the axle nut. Measure the torque required to keep it turning. Repeat for the other side.
The spec is 29-58 ft-lbs. Don’t be surprised if you get a lot less on a used LSD.
I would check both directions and both sides several times and both warm and cold.
LSDs are easy to service, just not inexpensive.

Best,
Grady

Take it out at night, stop in a quiet location, put it in first, drop the clutch at 5000rpm. If your wheel spin results in two dark lines, your LSD is good. :D

But serioiusly, Grady,

Why put the car in gear to do the test? I would have thought that the wheels can't turn at all if you have it in gear? Please elaborate!

Thanks, George

George,
You are correct and I was wrong, both sorta. Yes, it needs to be in gear but the other wheel not blocked. Turning one axle flange will overcome the prescribed resistance. The other wheel will turn the opposite direction with resistance. The differential gears will be operating and all (both sides) clutches will be slipping under the pre-load. Since there is no engine torque being transmitted, there is no additional force applied to the clutches.

Again; test both directions, both sides, warm-cold, multiple times.

Dumb old me.

Best,
Grady

That would be a low gear and hopefully the compression is still good, or there's a breaker bar on the crank pulley wedged/visegripped to turn in the right direction.

Uhhh... I'm still not sure I get it. Can I do this with the trans out?!

Chris,

Yes, you can do it with the trans out. You need to be able to put it in 1st gear and then prevent the input shaft from turning. This can be by reattaching the trans to the engine or by using an old clutch disc.

If the transmission is partially dissembled, put it in two gears.

If the LSD is out of the transmission, Porsche’s recommended technique is to hold the differential housing in a vice and turn an axle flange with the indicating torque wrench.

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Best,
Grady