savyboy

How do you feel about these observations per Roland Kussmaul and Porsche Powertrain Engineers?

"The mechanical LSD in the GTx streetcars has no preload on the discs. That means, you cannot find out if the LSD works correctly by just jacking the car up and turning the wheels manually! Nothing will happen in that case because the diff isnt working.
The reason for having no preload on the system is because the car would be a lot less manouverable in park-in situations and would therefore lose some of its "everyday driver" characteristics.

The LSD of a Cupcar has preload on the discs and therefore reacts differently on the jack, although the hardware is very similar.

To find out if the LSD is in good working condition choose a long 3rd gear curve (or a big enough space to drive a neutral 3rd gear circle), go with partial throttle and play with the accelerator (more load/less load). The car will change its radius noticeably because of the diff working. (On overrun its 40% and on throttle only 27% lock).

On all GTx projects of the past the LSDs where all still within spec after 30.000 km of hard racetrack use. On dissassembly there was no critical wear and tear on the discs or on the ramps."

Matt (GTGears) your input is valued and appreciated especially?

Serge944

This is interesting. My car definitely does this, but I always thought it was due to the weight transfer from going on/off throttle.

malmasri

Thank you Savvy for this info,By replacing the LSD with a more agressive one the difference is quite noticeable to a non engineer, me, and that is all that matters..., I find it difficult to diagnose the LSD with a long 3rd gear circle ( more throttle will always cause a larger radius despite the LSD function)

P.J.S.

then what causes a 996-3 with 16000 miles to wag it's *** end under straight-line threshold braking if it is not a failing diff?

Or a 3600 mile .1 RS to exhibit the same characteristic?

only to have a dealer rebuilt diff in the 996 and a new guard unit installed in the RS completely rectify the situation?

car makes all sorts of mechanical noises in stock form but a diff that will last is out of line?

fwiw my 40:60 guard is a peach in daily driving etc

on the 996 the dealer tested per the factory instructions and verified it was out of spec and rebuilt it under CPO

I did not bother on the RS as I did not want to mess with it frequently - so guard diff and done and I am expecting to get at least triple the life of the factory diff and so far with no downside on street or track.

how about a factory "option" for a diff-s (a la rumored pdk-s) or heavy duty diff and just put a cup diff in...

TRAKCAR

I can see many buyers would return the car to the dealer the way it drives now with the CUP 38/52 LSD.
It pushes the nose way wide and reacts too much to gas on /gas off on on ramps and off ramps I imagine.
Keep in mind OEM the car does not suck on the track (Just the Ti center exhaust does) it even comes with screens in the front bumper now and the proper seat. They do listen!
I don't mind the nose going wide and tucking back in and it makes the car so much better on the track, no tail wagging and way more planted on throttle, but I can understand a CUP LSD has no place in a street car.

I wish it came with it, but I wish it came with the Clubsport package, endurance pads, slotted rotors, clear bra everything, data acquisition/tripple camera system, Cup lips and spoilers from the factory as well....

mdrums

Savyboy...anyway you can find out how the LSD that came as part of the Sport PASM package on my 2009 Carrera S PDK differs in materials, ramp and lock up settings and longevity than a current GT3 street car LSD?

thanks!

FFaust

Kussmaul's comments make sense but are still highly suspect per PJS' post above.

Previous owner of my car had cup gearbox, so my current LSD is, for all intents and purposes, new. I will keep a very close eye on it's behavior and eventual deterioration.

mooty

that's what pretty much copans told me long ago.

i dont know if my LSD is working or not. but in ALL my GT3's, i have NEVER had tail wagging under hard braking on straightline, unless it's wet. now, if someone wants to buy me a new PMNA or Guard GT2 diff, i be happy to do some experiments ;-)

P.J.S.

i dare not argue with the master... but my personal experience is so far from this statement that I am thinking I am doing something wrong.

996FLT6

Mooty doesn't late brake ^he drags brakes which hides lsd's affect on braking. 2 different approaches to braking but similar lap times either way(^he faster in some spots I'm faster in some spots). I late brake alot and I know LSD is fried when it happened. Mike

Crazy Canuck

My diff was shot. Rear end wagged like a horny labrador retriever under braking.

With the Guard GT2 diff it doesn't move. Big difference.

tcsracing1

my diff was toast too. *** wiggle under hard braking... what gives right?!

CRex

Not with Kussmaul here, based on personal experience.

My 997.1 started showing the same symptoms at 6k miles--loose tail on hard braking plus inside wheel spinning when I mucked around in powerslides... put in the Guard clutch pack and the symptoms were immediately gone. Even transformed the car from mid-corner understeer to mild oversteer. It was THAT obvious.

I remember Mike at Guard at some point commented that the Gen 1 and 2's share the same diff+clutch pack so it'll only be a matter of time before the problem resurfaces in the 997.2...

Pete: on a GT2RS I can only imagine the diff to fail even sooner... you might as well preorder one from Mike now

ADias

I also have LSD on my PDK diff and feel the LSD working every time I brake hard on uneven surfaces - straight as an arrow.

996FLT6

Doesn't 997s have abd? If it does it'll trigger 1st before even LSD comes
into effect. Mike