996 2005 GT3 - Testing Limited Slip Differential(LSD)

[gofaster]

Hello!

Before dismantling for visual inspection, I would like to quickly torque test the Limited Slip Differential(LSD) on a 996 2005 GT3.

Can I rely on the following procedure to determine wear and tear prior to bench test and visual inspection?(Car has 28,000 miles)

1. Raise and remove rear left wheel.

2. Confirm gear box neutral, parking brake off, and remaining wheels blocked.

3. Set torque wrench to 5 NM then rotate left rear axle nut counter clock wise... slip?

4. Set torque wrench to 10 NM then rotate left rear axle nut counter clock wise... slip?

5. Set torque wrench to 15 NM then rotate left rear axle nut counter clock wise... slip?

6. ??? What torque is acceptable; Any other suggestions ???

Thanks.

[clord]

Hi Gofaster..... I've had similar questions about my '04 GT3 diff and GT3 Cup car diffs......and was still a bit confused. So I sent your write up to a well respected GT3/Cup Car mechanic/driver friend of mine. He has built Getrag trannys and GT3 race motors and, as a driver, knows how the LSDs act and feel on the track. Here is his response to your post:

"It is sort of valid. It checks the amount of remaining preload. A new Cup diff will probably hold 200Nm in this test. A well used GT3 diff will probably be near zero. This does not mean the diff is "broken", instead it is worn and less effective than it was when new.

The stock GT3 diff does not perform like a real racing diff and people expect them to. In my opinion, the car is better on the track if it has a real racing diff.

On the other hand, for normal sporting driving the stock diff is ok."

Remember that you are measuring just the preload in the LSD clutch pack...the ramps are still acting to compress the clutch pack according to their angles..... In our case, different angle for acceleration versus overrun....nominally 40% on accel, 60% on decel.<br style="mso-special-character:line-break"> <br style="mso-special-character:line-break">

[RR GT3]

Good afternoon. If you were to rotate one rear wheel while the car was in the air and the opposite wheel did not rotate, would that mean the diff is shot? Thanks, Warren

[clord]

RR..... Not necessarily. See my post above.

[RR GT3]

CLORD - Thanks for getting back. I am in the process of replacing the guts of the diff to get closer to what's needed at the track. This car sees between 20 and 24 track days a year so I'm guessing the Nm test will come out at zero. The clutch needs to be replaced as well. So it's a good time to do it all. Your post prompted me to look around much more and will be going to a real racing diff or close to it. I'll put up with it for the little street time it sees. Not sure what ramp ratio we'll be going with. (Not doing this work myself.) Regards, Warren

[gofaster]

Craig,

Thanks for getting opinion of mechanic/driver friend; information is helpful.

-David

[david_yorkshire]

not sure why you don't think the GT3 doesn't have a racing diff

it's essentially same (different plates ) to the cup car unit, which certainly is a race car !