View Full Version : LSD types info

10-20-2003, 10:56 AM
Hey, just reposting this for Kev to put into FAQ. Sorry if you have already read it and thought this was gonna be something new. And no i still did not edit the gramatical errors... bah.

There are various types of LSDs. For our cars, there are Viscous, which uses a fluid filled sac taht expands with heat (Fritction) to lock the output shafts, and then there are mechanical. Mechanical means that the LSD in engaged or not due to interaction between 2 (or more) set, mechanical parts. This category inclused CLUTCH and HELICAL type LSDs.

For road racing, Helical type is more desirable, because it acts like an open diff while turning in and such. If I am not mistaken, it does not lock the two output shafts to spin at the same rate, but rather it biases torque to the wheel with more grip up to 80%. Shit, you know what, its been a while. If I weren't on a slow ass computer running Windows 95 i would search google for QUAIFFE or HELICAL LSDs and dig up some diagrams and a more in depth explanation.

Ok, other type of Mechanical LSD, clutch type. Clutch type LSDs use a center cam that moves under torque changes within a casing. The casing is 2 parts (L and R) and is symetrical in that sense. However, the cuts in the casing making the notches for the cam to slide in are not. That determines 1, 1.5, or 2 way LSD. As the cam slids in the notch it pushes the casing outward, which engages a series of clutch discs, some attached to the cashing, some to the output shafts. When engaged, both output shafts will rotate at the speed of the casing, making both axles, and subsequently, wheels, rotate at the same speed.

Now back to the notches:

A 1 way notch is cut like an upside down triangle. While the cam can push backward against the tapered edges, expanding the casing, it cannot push forward against the flat surface. Therefore under acceleration torque (cam rotating backwards) it will lock, and under deceleration torque, when the cam is forced to rotate forward due to forces from braking, engine braking, etc.. it will just contact a flat "wall" and the casing will not expand.

A 1.5 way notch is like an upside down triangle with a half trangle on top of it. During acceleration it will expand the casing at one rate, and during deceleration, it will still expand the casing, but due ot the cuts' higher angles, it will require more force to move the casing apart. Therefore, only during Very hard braking will it have enough force pushing it forward to expand the casing.

Need it be said that a 2 way then is shaped just about like a diamond? Where it requires almost the same amount of acceleration or deceleration to force the casing apart. Usually, the top cuts are slightly more dramatic, making the 2 way still require slighlty more deceleration force to push the cam to expand the casing.

Ok, there is more. The more the casing expands, the more clutches contact each other, and the more the output shafts get locked into the same rotation. Now there are adjustable diffs where you can set a breakaway torque. That means that the cluch discs get moved closer together or further apart to dictate the SOFT, MED, or HARD setting. The closer the clutch plates are to each other, the sooner the output shafts, and thus the wheels, will spin in sync.

*I didnt edit any gramatical or spelling errors. Yes, i know they are there. Deal with it.

10-20-2003, 11:02 AM
Thanks, Lindsay.
Away it goes!