Lsd or positraction

[Juan Saca]

How I know if My 911 carrera 3.2 1989 G-50 is equiped whit LSD or positraction ?

[lupin..the..3rd]

What is a positraction? You can check for LSD by jacking the rear of the car up. Spin one rear wheel by hand. If the other rear wheel turns in the same direction, you have a LSD, if the other wheel turns in the opposite direction, you have an open differential.

[Flieger]

Posi-Traction was a GM trademark for their limited-slip differential (LSD). It is a term from the muscle car era.

There are two basic types of limited-slip differential. The "true" LSD uses clutch friction plates, preload springs (bellville washers I believe), and ramps cut on the spider gear cross shaft in order to apply clamping load to the clutch plates and attempt to limit the difference in wheel speed or to lock them together. The ultimate rendition of this is the spool as used in cars such as 962s and 935s which is simply a lightweight, strong, solid metal (Titanium usually) shaft connecting the two sides such that both wheels turn the same speed.

The other type of LSD is the torque-biasing type. This type uses helical or worm gears to transfer torque from the slower wheel to the faster wheel (so inside to outside). The gears provide a mechanical advantage such that the torque from the engine is apportioned between the sides in a certain ratio or bias. The issue with these is that they act as an open differential if the inside wheel starts spinning or under deceleration. This makes it good for autocross but does not provide the stabilizing effects of a clutch-type LSD under braking that track guys usually want.

The common name for torque-biasing differentials is Torsen (torque-sensing), but I believe this is also a trademark that has become a generic term like Kleenex tissue.