560SL positraction

[Litton]

I am under the impression the all 560Sl's came equipped with posi as a standard feature. Sometimes I think I have one...other times I'm not so sure.

For example, on the dirt ortion of my driveway, both wheels will spin on command. On hard acceleration on pavement, both wheels will laydown massive clouds of blue smoke and spin like crazy. However, if I am turning an tromp on it, only the unloaded tire spins.

Can anyone shed any light on this topic.

[Walrus]

You are partially correct... The 560Sl came with Limited Slip, not positraction. According to my research, all 560SL's came with limited slip diff. The limited slip relies on brass slip-ring mechanism which, over time, becomes less effective. This renders the rearend more akin to an open diff like earlier SL.

There is a fundamental difference whether the car is moving straight forward, or in a turn.

Your symptoms imply the limited slip is still functioning... If the diff were to lock up, steering would be compromised and the car would tend to understeer terribly (heading you for the ditch at a rapid pace). The fact that the unloaded tire is spinning does not mean the loaded tire is not pulling or applying force to the ground. The loaded (outside) tire has to turn faster to cover the ground relative to the inner tire (as the outer tire is traversing a longer path in the same time period). The inner tire is probably spinning because it is trying to match the outer tire's speed. If this is the case, the tire has only one option, and that is to break free and spin.

Perhaps someone here can add with the correct way to test (without performing numerous burn-outs)... I can't remember right now. I believe your diff is functioning normally, and is functioning as was designed.

Hope this helps.

[Litton]

OK, that makes sense. I imagine there is a pre-load adjustment on the brass slip ring assy to accomadate wear. These must act like a clutch. (NOTE: I am alergic to ditches)

[Walrus]

I wouldn't worry too much about the ditches... If the limited slip is worn (out) the axle will definitely not lock, so no worry of inducing the ditch-cleaning understeer...

[Ben]

To test if you have a limited slip (or other traction device) jack up the rear of the car. while spinning one wheel, note the direction the other wheel is spinning. if it is spinning in the opposite direction, or not at all, you have an open differential. if it spins in the same direction, you have a limited slip, or something similar.

[230/8]

Litton:

Your limited slip sounds like it is working properly. The internal clutches of the differential are designed to provide a locking of the two axles via the clutches, or cones depending on the design. These clutches join the axles so that in a straight line the two wheels will lay down those two long patches of rubber. Without the LS, the unloaded wheel, usually the right one, will lift slightly, break traction and then all the power transfers through the differential spider gears.

When you make a turn there is a need for the inside wheel to turn at a different (slower) rate than the outside wheel on the turn. The differential spider gear set allows this to occur. When you have a limited slip, (other names are positraction, traction lock, sure-grip, etc.) the internal clutches are designed to "slip" and release their lock on the two axles so that the necessary speed differential (note the terminology, that is why the rear gear set is called a differential) between the wheels can be achieved. There is usually a break-away torque value designed into each LS differential. If you raise the rear off the ground, a normal open gear set allows one rear tire to rotate in the opposite direction than the other (spider gears again). With LS, they rotate together (locked up by the LS clutches) but, if you restrain one wheel a bit (like when you make a turn) it will break the clutch locking action at that pre-determined torque so that the two wheels can achieve the the required differential speed.

I'm sure there is some complex MBZ test method for determineing whether your unit is operating properly IAW MBZs specifications. But here is the fast, simple and more fun way. Set up on a clean straight dry road. Make sure your tires are equally inflated. Check for cops, if all clear hammer the gas and peel out like hell. Go back and measure those black marks. They should be equal length, more or less. If so, fugedaboutit. Diff's fine. If not, check your bank balance and if you're flush, get a new diff if you fell like you just gotta have LS. Unless it's making noise, an ineffective LS will not cause you any problems, it just won't give you the benefits of LS if you need them (think snow).

For what it's worth,

230/8 (former street racer, but reformed for many years)