Checking LSD When Trans is Out of Car

jamesjedi · 09-26-2011, 03:57 PM

Hi,

Can I check the 915 LSD by spinning the shaft inputs when the box is out of the car?

Thanks for any help.

James

prschmn · 09-26-2011, 04:40 PM

Look for roughly 15 Ft pounds to slip the clutches.

Matt Monson · 09-27-2011, 07:22 AM

According to Porsche's own published service manual, for a 40% configuration the working range is 30-57ft/lbs. For an 80% race configuration that goes up to 43-85ft/lbs. When it drops below the minimum number it's time to rebuild.

Regards,

Matt

jamesjedi · 09-27-2011, 08:04 AM

OK. I have a silly question, if the transmission is just sitting on the floor, how do I check with my torque wrench?

Thanks.

prschmn · 09-27-2011, 08:22 AM

Just lock one drive flange and turn the other. Matts numbers are workable for new rebuilds but assuming this is a stock/street car you can survive with less.

jamesjedi · 09-27-2011, 08:40 AM

I assume that there is a nut to put a socket on?

Matt Monson · 09:43 AM

Quote:

Originally Posted by prschmn

Matts numbers are workable for new rebuilds but assuming this is a stock/street car you can survive with less.

So you're saying that you know better than the factory? The street diffs are 40% as delivered and the lowest number I posted is the minimum that Porsche says is within spec. When it drops below that it's worn out. To each their own, I guess.

And I don't recommend ever testing it on that drive flange bolt. That bolt is only rated to around 45ft/lbs. If you have a diff that tests higher, you can break the bolt or damage your LSD. What you need to do if you are going to test it is make a tool that spans the flange (some square bar stock with a bolt welded to it is the best replica of the factory tool) that you can put a torque wrench on. You install a couple of used CV bolts into the flange and brace it off the tool. Then you toss the CV bolts in the bin when you are done and don't reuse them on the car.

jamesjedi · 09-27-2011, 10:23 AM

This is more complicated that I had hoped. Is there another visual confirmation? I understand that the stamped numbers are unreliable.

Matt Monson · 09-27-2011, 10:53 AM

Are you trying to determine whether or not it has an LSD or are you trying to determine whether or not it's worn out?

If you just want to know if it has an LSD, spin one flange and look which way the other one spins. Same way it's an LSD. Opposite direction it's open.

jamesjedi · 09-27-2011, 11:31 AM

Yes, also determine if it is working. I imagine that most of these are getting tired.

jamesjedi · 09-27-2011, 11:46 AM

Thanks for everyones help!