I picked my car up this week with a repacked LSD. Warranty:-) from the dealer. Like new! I understand that there is another GT3 in line for the same. Can not wait to wave you by next year.

 

I thought your car was over 50K miles...no? Anyway glad they covered it! Now you can hear that beautiful chattering once again.

 

I think that part is still covered by the drivetrain warranty..?

 

51K and covered I did an extended warranty. . I really notice the fix with lifting and braking at speed!! Straight as a bullet zero hunting...

 

Ron: what's up with the SC? Hope it works out

 

It worked out...PPI showed broken head studs; seller is footing the bill. Car should be here by end of Jan. I am psyched. Don't want to hijack this thread though, so I will post stuff when it gets here safe and sound.

 

Can you elaborate more? My car also make some kind of jerk when you totally lift off from the gas when steering is not straight. Just wondering whether my diff needs an attention. Thanks.

 

At say 120mph+ when I lift and brake, the car is completely flat straight. When my dif was worn it felt like the nose was hunting. The reason was that the rears were not locked. Now that they are again(60) all is well.

 

Resurrecting this old LSD thread.

I'm clueless about LSD's and am wondering what the numbers denote.

Also, what would be the driving difference in going from stock to say 80/80?

 

This article about Guard LSDs has a ton of good info on how these locking numbers translate to handling:
<http://www.guardtransmission.com/velocity.htm>

 

Just had the cup car plates put in mine as they were shot at 20k miles. Probably been shot for a while in fact!

 

Very interesting but doesn't clearly state what lock under accel/breaking achieves?

breaking = understeer to help stabilise rear from coming round? If so why would you choose a higher lock ratio or a lower one?

accel = power down on exit, or even going straight on crappy surface. Again what dictates the ratio you pick?


Also any idea what lockup the GT3s come with vs the cups? Is there a reason to covett a Guards case rather than the OEM one?

 

1: 996 and cup are the same 40/60. The 997 GT3 has a 28/40. Cup uses better packs. I know of no ALMS or Rolex that use them all go with others. Guard is the most used I would guess at 50/80.
2: Reason for the bigger number on lift is weight transfer.
3: Guard is a much tougher product and is adjustable. 40/60 or 50/80.

 

by Andrew Warren, San Diego Region

Have you ever wondered what a limited slip differential is; what is does; how it works? When your car turns a corner, its outside rear wheel must travel farther than its inside rear wheel. The open (non-limited-slip) differential allows that to happen. It's a clever arrangement of gears that can transmit torque to either the left or right wheel and still allow the other wheel to rotate at a different speed. In fact, you can hold one wheel completely motionless and still drive the other wheel.

Limited-slip differentials (LSDs) work the same way, but they LIMIT the differential (the "slip") between the two rear wheels. The main reason for wanting a limited-slip is to improve traction in a turn. In a hard turn, the inside rear wheel will tend to lift off the ground (either completely or just partially) due to weight-transfer to the outside wheel. Because of the way an open differential works, the engine torque is directed to the wheel with the LEAST amount of traction, so in a situation like this, the inside wheel will tend to spin -- losing traction -- and the outside wheel, which is in the best position (since it's heavily loaded) to drive the car through the turn, will just coast along.

A limited-slip differential will allow SOME slippage of the inside wheel, but it will still direct a significant portion of the engine torque to the outside wheel where it can do some good. This, by the way, is the reason that I don't recommend using a rear sway (or "anti-roll") bar on a car with an open differential. The sway bar tends to pull the inside wheel off the ground in a corner, which is the last thing you need if your engine torque is going to go to the wheel with the least amount of traction.

There are numerous LSD designs. Many, including Porsche's LSD, use friction plates (like clutches) to accomplish the torque split. Some (like the Quaife) use an extremely clever gear-only arrangement to accomplish the same thing. The clutch-pack LSDs are probably more durable and are easier to modify for varying torque splits, but they wear out and need to be rebuilt every once in a while. The Quaifes contain a whole bunch of little gears, so they may be somewhat fragile, but on the other hand, they never go out of adjustment.

Some racers like to use a completely LOCKED differential, in which NO slip is allowed between the rear wheels. You can spot these guys in the paddock pretty easily -- they're the ones who can't make U-turns. However, the tendency of locker-equipped cars to just drag their inside rear wheel in a turn causes really bad corner-entry understeer.

 

Thanks - still not clear how a 40/60 vs 50/80 would feel different?

I'm stuck with cup diff packs at this point as order is in and parts in transit. Oh well probably good enough for the road. Also I thought the ramping was more agressive with cup plates which is meant to help? Bit puzzled though as the guy building it for me said he could change lock up rates etc using different shims etc. which doesn't tally with what you are saying. Also he said Porsche motorsport offered various options themselves.

Interesting that Andrew Warren thing as he seems to have dismissed the lack of lock up under breaking with a clutch diff vs a Quaife ATB.

p.s. at 50k miles your diff must have been dead 5x over!