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LSD


matt325
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Has anyone tried the limited slip differential test in the Spec3 rules (9.3.11.5)? I easily pass at 0 ft lbs of torque which is well below the 70 max allowed .

 

I noticed when changing tires a few weeks ago that the rear tire would spin pretty easily when tightening the lug nuts (the other rear tire was on the ground). I am pretty sure, but not 100%, that I used to be able to just about torque the lug nuts of the rear wheel with it in the air.

 

I think my LSD is no longer limited. I guess ten years of autocross and track have taken their toll.

 

But just want to hear from someone else that the rulebook test is viable.

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  • 2 weeks later...

I would appreciate it if any one with an LSD can take a few minutes to check theirs per the process in the rulebook and confirm I am not doing something wrong.

 

I am about to take out the diff to replace the clutch plates, and I want to be *really* sure since if screw it up, its a $1400 rebuild.

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Was the car in gear?

 

No. I would not expect the wheel to be able to rotate with the car in gear because the torque from the wheel would try to turn the driveshaft which is connected to input spline via the gear which is then coupled to the flywheel via the clutch disk. So testing the LSD with the car in gear is effectively testing the transmission clutch, not the differential clutches.

 

9.3.11.5. If a limited slip differential is fitted, it must breakaway at 70lb-ft. or less. The lockup will be checked at Impound and within 30 minutes of the conclusion of the race. It will be tested at the center hub nut, using a 30mm socket and commercially available ½” torque wrench. The car will be placed on solid pavement, the right side of the car will be jacked up until the right rear tire is free from the pavement, the transmission will be placed in neutral, and the parking brake, if present, will be released. The torque wrench will be placed at the nine o’clock position with the socket on the center nut. The torque wrench will be set at 70lb-ft. and pushed down. If the differential does not breakaway, a second and impartial similar style torque wrench shall be used in a second test, immediately following the first test. If the differential does not breakaway using the second torque wrench, the car will be disqualified from the preceding race and the DQ will be noted in the car’s logbook.

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Matt, I could check for you this weekend but I don't think I have a 30mm socket...if I come across one, I'll check it out for you.

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Andrew,

Thanks! At this point, I would be happy to know if your wheel just does (or does not) rotate per the test procedure. You can just try turning the wheel by hand, or, use a torque wrench on a lug nut. The 70ft-ft lb won't be exact, but it will be good enough.

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