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Geary Geary is offline
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Join Date: Feb 2003
Location: Kailua, Bend, & Tamarack
Posts: 1,573
The Zexell Torsen originally available in the 968 is no longer available. The replacement offered by Porsche is a cast, medium quality, 40% (40/40) LSD. Not nearly as nice as the Porsche Motorsports 40/60 (more accurately 45/65) version, but nicer than the street 993 version.

The 968 is indeed a G50-sized differential. The differential is probably the only part interchangable between the two transmissions. I'm not certain if it has the 3 speedo ring holes necessary for the 5-spd G50.

The Torsen TBD (or any TBD) will "wear out" eventually. They slowly loose effectiveness as the individual gear bores wear egg-shaped. The quality of BRAND of TBD determines the longevity of the unit. But certainly they don't require the somewhat regular maintenance of an LSD.

The main issue with the 20/80 or 20/100 LSDs is the material of the friction discs that were originally installed. Instead of the high quality material used in earlier 915 & 930 LSDs (plasma-sprayed steel), the "carbon" or "horse puckey" material was used. This material is rather ineffective after a SINGLE weekend on the track, or probably 5-10,000 street miles. (Obviously, a number of factors determine how many street miles.) These pitiful discs CAN be changed for the superior type. Careful measurements are required to determine the exact shim stack for replacement. Life is 10-20 times as long with the better discs.

The "carbon" discs can also disintegrate, making a black mess of the trans oil.

The second main issue with the 993 street diffs is that you don't know if you're getting the 4-friction disc version or the 2-friction disc version. The two friction disc version has half the stated locking effectiveness.

All that said, even a worn LSD helps a street car. It just wouldn't perform well on the track.
Old 10-13-2005, 08:18 AM
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