Limited Slip. How does it work?

[davidmash]

Dumb question but how do I know if it works. I thought it is supposed to "lock" the wheels together sort of. We just had a ice storm down here and I thought that it was not supposed to let one tire spin freely? I could not see it from inside the car but when making a turn it seemed as if one wheel spun like crazy and the other just spun at normal speed to get me out of the corner. Is that what it is supposed to do? I have a 1987 16v euro version.

[sixto]

I'm not familiar with MB LSDs but you can check www.quaife.co.uk for an example of a good LSD that doesn't use clutches or viscous fluids.

Sixto
91 300SE
87 300SDL
83 300SD

[bjcsc]

David:
Yes that is what your diff. is supposed to do. Now for more than maybe you wanted to know. Here's the way it works: Basically, there are three types of differentials: open, limited slip (or positraction) and locked. To understand how they work, you have to think about torque in a different way. Think about it as no resistance = no torque. The maximum amount of torque is limited by 2 things: power and traction. In an open differential, the same amount of torque is applied to both wheels, but the torque is limited by the traction. Thus when one wheel slips, the amount of torque = zero in both wheels and you go nowhere. In a limited slip differential, clutches and springs are used to basically set a minimum amount of torque required for them to slip (so you can turn). When one wheel slips, the amount of torque drops (gets further away from overriding the clutches and springs) so the other wheel keeps turning and you get out, though at reduced power - your exact situation. You can think of it like a locked differential that unlocks under a certain amount of torque. In a locked differential, both wheels always turn at the same speed, regardless of whether or not they are getting traction, ie. one wheel wouldn't slip even though it has no traction and the other would get you out without you really noticing which wheel really had traction. The other thing that occurs with locked differentials is difficulty in turning as the outside wheel can't turn faster than the inside wheel in turns on pavement and thus hops to spin in the air, putting tremendous stress on all of the axle components. You may have seen part time 4wd vehicles (like Jeeps!) do this when they are engaged on concrete. It's a similar situation, but in this case it's due to them not having a third differential to accomodate the different speeds of the front and rear axles. So they're really hopping "front to back" and not "side to side". Full-time 4wd vehicles have three diffs., one for each axle and one between the two. Nonetheless, locked diffs are limited to off-road applications. Anyway, you're in good shape. (this got kind of long - sorry) HTH

[sixto]

Here's even more info:

http://www.houseofthud.com/differentials.htm

... and still no answer to why your wheels were spinning... if they were.

My guess is that one wheel got on something slippery but the LSD continued to send power to the wheel with traction allowing you to continue the turn. So one wheel was slipping since the LSD tries to keep both spinning.

Sixto

[oldsouth]

Some limited slips are electronic also. This kind uses the brakes to limit wheelspin on one tire in order to transfer power to the other tire.

[davidmash]

Thanks for your info guys. At least i know there is at least one thing on my car that works right lol.

LSD's are great where one drive wheel has good traction and the other doesn't (e.g., left wheel on dry pavement and right wheel on wet pavement) because both wheels still get power even though one can't use it at the moment. And they are even better when powering through a tight corner where body lean unweights the inside tire but the outside wheel keeps driving (an open differential would allow the inside wheel to spin and reduce the outside wheel to coasting).

When both wheels have no traction (such as an icy road or one covered with packed snow), though, I'd rather NOT have a LSD. The reason is that when both drive wheels are spinning as they might when your engine overpowers the available traction, other torque forces in the car start to affect the direction of your hockey puck. What usually happens is that the tail end (in a RWD car) will head toward the curb putting you sideways to the flow of traffic.

An open (standard) rear end won't do that in most cases; instead, you will just spin one wheel, the other one won't turn at all, so you stay stuck where you are.

Why do I prefer no movement? Because then the idiot behind you that can't stop will hit you in the energy absorbing bumper and drive your head into the headrest instead of hitting you in the driver's door, driving your head into the side window glass!

[xp190]

M D Nugent

That is an awsome reply!
I was thinking of getting an LSD for my 190, but after reading your reply I think I will stick with my standard.

I did notice that on snow my car stays in the direction it was traveling in when one wheel slips. Also, once I had a full car of people and I had to brake a bit harder on wet asphalt, and one wheel slipped but the car stayd in the right direction as well as stopped right on

Makes me feel all warm and fuzzy inside

I'll go hug my differential when I get home

xp

I put a Quaife (LSD) in my for-competition-only Porsche 914, and it cut my lap times by 5%, so LSD's are semi-mandatory in racing, but you shouldn't really drive around corners at 10/10ths on the street . . . regardless of whether you're in a MBenz or not.

Putting a LSD on a non-AWD/4WD car on the street is in the same league as substituting carbon fiber parts. The logic goes, "Racers have them, racers are cool; if me have them, me be cool." . . . I don't think so.

[kip Foss]

David,
Check out a site called www.howthingswork.com. I think that is close to the name. It has great diagrams and dirt simple explainations.

[davidmash]

I think I like my LSD rear end. If I understood what BJ said a few posts up It seems to help out in snow and ice. I had only one wheel with traction and the LSD help prevent me from getting stuck. Since if I had a open rear end, it would not have sent any power to the wheel with traction. Seems to me like that is a good thing and I do not see a down side for day to day driving.