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Locking Differential question

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Car in question is a '99 C2. Option sticker indicates:




I had it up on a lift and was turning the rear tires, but the other rear tire was turning in the opposite direction. Any US built car I've ever owned with LSD, the wheels would spin in the same direction. Anybody have any experience with this? Is the locking something that is somehow regulated by the PSM?


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From the Tech Book...

"...vehicles have a mechanical limited-slip differential and ABD as optional equipment. The limited-slip differential has different locking values under load and under deceleration.

Locking value under load – 25%Locking value under deceleration – 40%

The lower locking value under load significantly improves cornering behavior. The higher locking value under deceleration reduces yaw due to throttle adjustments in bends and therefore has a stabilizing effect on the handling of the vehicle."

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OK, I'm really confused now. I'm looking at Adrian Streather's 996 The Essential Companion and on page 254 he states:

"All 996 models up to and including 2003 with PSM installed as an option were not permitted to be fitted with any other form of rear differential apart from an open one. This is because the mechanical action of the LSD interfered with the operation of the PSM."

Then on page 299 under the discussion of PSM he writes:

"PSM was originally installed as standard on 1999 996 C4...However it was available as an option for the RWD Carerra model range (option M476), but the cost was prohibitive because along with the PSM syatem, came a different engine, e-gas and a new engine mgmt. software version."

I don't have option M476, and I can see a throttle cable under the car and r&r's one on the throttle body when I did the AOS job so I assume I don't have e-gas...

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I discovered what may have been the source of confusion on my end. I was looking at the owners manual that came with the car and other than a printed date of 5/03, I can't tell what year it's for - though clearly not 1999! So I had been looking at the dash diagram and index where both referenced PSM. When I finally got close enough to my dash button, it clearly reads "TC Off".


BTW - do you know where the serial number is located on the transaxle? I found a few cast-in numbers, but nothing that resembles the trans serial number that is listed on the build sheet printout I got from Suncoast.

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Found the answer to my original question when I finally found my trans serial number. Build sheet says car should have trans serial number GA96002011587 and currently installed transaxle is GA96001022944. Looking at this chart in 996 The Essential Companion the LSD unit must have been replaced at some point with an open unit. :eek:

Kind of sucks, but from what I read, the LSD needs rebuilding fairly frequently. I'm not planning on doing much track time and the TC will help out in snow if necessary. Also, the replacement is 11,357 units newer! Still a bit bummed though. :unsure:


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