Hello Everyone,

I'm curious as to the symptoms of a failing LSD/Clutch.. Recently my car has been getting progressively jerkier as I drive it. Its harder to shift while cornering, and at partial throttle it lurches forward and back lightly, which is a pain to drive around. I also hear popping/grinding noises when I make slow corners in first/second

My clutch is on its way out, I know that- It is the OEM clutch but I'm not sure if thats whats causing these symptoms. It slips sometimes on boost in 3rd/4th... it just depends.. sometime it doesn't slip *shrug* It chatters like crazy on reverse (even though its a dual mass flywheel).

Things I've ruled out:

- Transmission mount is a brand new race mount. Upon installing it, it did improve a metal-hitting sound I would hear while driving, that turned out to be the trans mount being broken.

- Gearbox oil is new, so it cant be something with the gears (unless its a bigger problem... yikes)


I fear my lsd is shot... I have 4 track days and 2 roll-racing events on the lsd... I wouldn't consider myself an aggressive track driver, but not a slow one either...

Any advice would be appreciated!

 

re: the LSD --> how bad is your tail-waggle on highspeed/hard braking?

My OEM LSD was 48k miles first time at track and WHOA that thing was twitchy. gtGears rebuild and it brakes in a very nice straight line now.

 

Stock clutch and 1.5 bar you are pushing ?

My OEM clutch was done 200 hp ago and this new one is right at the edge of it's possible power/torque

upgrade that clutch mate

 

xlnt point. if yer tail is waggin while yer brakin then yer lsd probably aint workin so good

 

I haven't noticed any tail wagging on acceleration or braking. Maybe just a very small amount.

 

the lsd is designed to limit just those things. but you know your car better than anyone else. i don't know how the stock gt2 lsd feels. never drove one sorry to say.

if you feel you have less of what the lsd provides? ( traction in off camber events and power still to a wheel with the least "weight"? e.g. cornering/braking ) then it may be the plates are in fact in need of replacement. plate type lsd's wear out. i think you're on the right track, but really... wtf do i know!? no expert here....

a major symptom as noted upthread of a failing lsd would be just that. less of its ability to do what it "prevents' or diminishes e.g. tail wag, while trail braking, out of corners etc. at least as best i can articulate it.

 

It seems like I need to be on the track again to see if it isnt working. Its hard for me to tell from just driving around. I'll take it to a shop and have them test it. Hopefully its just my clutch. That thing has seen a lot... Of power... Haha

 

The stock OEM LSD that Porsche put on the GT2/3 has a minuscule preload, less than 10 lbs actually. That is why the LSD wears out within a matter of a couple of track days. A Guard LSD is generally shimmed to around 60 lbs of preload and Cup LSDs are sometime shimmed for even more. The preload on the LSD is what "ties" the rear wheels together and gives you that stability under hard straight line braking eliminating the tail wiggle. The OEM LSD does not have hardly any ability to do that even when brand new.

 

Makes me wonder why they didn't do it right from the factory...

 

Simple. The reason the factory did it with such a mediocre LSD is due to the fact that a vast majority of these cars will never see the track and as such do not need a motorsport type LSD. The goal of the OEM LSD is to provide an LSD that functions under street use and does so with minimum noise or chatter from the clutches when slowly turning, backing up, etc. The last thing Porsche wants is a bunch of guys bringing the cars back complaining of clicking noises coming from the LSD while they are negotiating the treacherous confines of a Cars and Coffee parking lot or while backing the car up into their driveway. The low preload is also probably chosen to minimize any push the car "might" exhibit while turning when road conditions are slippery as when on icy roads, etc.

 

^ that's instructive! can/would you describe the "push" of a properly loaded plate lsd as opposed to one with a low pre-load e.g. the oem gt2 unit?. I'm not sure i have that experience, and am curious as to how that might manifest. are you saying the lsd ..under certain conditions will actually "drive/push" the car even in an rwd config? or am i really missing "it"?

 

The preload of an LSD is the amount of force it takes to break the "tie" between the two wheels. The preload is set by shimming and the belville washer. It has nothing to do with the actual locking of the clutches which is caused by the internal LSD ramps and difference of speed between the two wheels. To oversimplify it, an open diff has zero preload as the two wheels are not tied together, hence the term "open" diff. On the other extreme, a solid live one piece axle has infinate preload as the two wheels are totally tied together. If the wheels are tied together, the car will roll in a straight line and resist any type of a turn. In fact, the only way it can turn is if one of the wheels starts scrubbing. On a slippery surface, it would be almost impossible to make a car like this turn. So, if an LSD has a 50 lb preload, that much force must be exerted to break the tie between the wheels. The higher the preload, the higher the force required to break the tie and make the car turn. Hope that makes sense...

 

as Powdrhound has stated, the OEM diff was designed to minimise negative effects while cruising on street, parking, etc by using a low-preload and relying heavily on the ramps to apply pressure when on power or decel. The Motorsport and Guard options force the plates to work full-time, adding stability(sometimes at the cost of rotation) and more consistent response to small changes...the materials are also better which adds lifespan.
OP, IMO something sound wrong with either the clutch in the release/engage part of things, or have a transaxle issue, have you checked the drive stubs coming out of the trans for play?(almost sounds like some weird binding issue..)

 

completely. all of it.. thanks.

 

I haven't checked the drive stubs, nor do I even know what this part is...

Does the guards lsd reduce daily-drivability? I usually drive my car in the winter/pouring rain too...