newton22

I don't know if it's just my car, but when it was on the jackstands, I was able to freely rotate the rear wheels even with the transmission in park. WTF?

I thought my drivetrain was having issues until I set the car back on the ground and parked on a slight incline without the parking brake, just to see if Park would hold the car. It did fine.

velvet fog

Did you look at the other wheel while you were spinning one? On a vehicle with an open differential (non LSD) when you spin one wheel with the driveshaft locked, the other wheel should rotate in the opposite direction.

Oxygen

Yup... it's the differential.

newton22

Oh, so if both wheels are spinning in the same direction in park, the wheels will lock?

my06clk

Actually they won't lock, but the force will be transmitted to the drive shaft.. And since the drive shaft is connected to the tranny which is in park, the car won't move.

Just about every car on the road has a limited slip rear differential, and this is exactly how it's supposed to work..

This is the reason you should never jack up the rear of the car leaving one wheel on the ground without using the E-brake. With one wheel on the ground and one in the air, the car can still move causing the jack to come from under it....

The front isn't as dangerous as both of the rear wheels are always on the ground.

velvet fog

If you have a limited slip and the trans is in Park, you will be able to rotate one wheel, but it will be verrrry hard or impossible to turn (depending on the type of lsd) and the other wheel should not turn.

whoover

I don't know about this. Practically no Mercedes have limited slip. Just SL65 and some AMG models with Performance Packages.

But even most limited slips will behave like this. In normal operation the wheels are driven by the prop shaft side of the differential, not the other way around. The job of the differential is to divide incoming torque between the two rear wheels. Open and limited-slip differentials do this differently, but because of the way they work, if you run one in reverse they pretty much do the same thing: spin one wheel with the other able to freewheel and the torque you apply is applied to spinning the other wheel in the opposite direction; spin both wheels in the same direction, or one with the other one locked, and the torque is applied to spinning the prop shaft. If the prop shaft is attached to an unlocked transmission, it will freewheel the transmission. If the transmission is locked, you'll be prevented from spinning the wheel.

my06clk

Yeah.. well my use of the word limited slip may or may not be correct in this case but the point being, open, or limited they all behave the same when the wheels are off the ground so they are all the same. Only the gear ratios/sizes are different per application.

These are 2.82:1 and 2.65:1 respectively for all W220's

check this out..
http://www.detali.ru/cat/oem_mb2.asp...SGR=350&SGN=03

I think I basically said the same thing except in one sentence as the O/p is not that technical.

whoover

I'm not sure what you meant by limited slip, but I think we agree it wasn't limited slip. Also, I'm not sure what final drive ratio has to do with anything. The link doesn't work, so I can't really see where you were going with it.

my06clk

Oh..the link was just a various parts listing and breakdown for the Differentials in mercedes cars.

Limited slip rear end allows one side of the wheel to gain a torque advantage over the other side as most cars have for cornering in high torques situations for example. Otherwise there is Positive traction which splits the torque evenly between the axels.This is great for straight racing, but not so great for heavy maneuvering or cornering at high speeds. A lot of old US muscle cars had positrac rear ends..

I believe All of the Benz cars are Limited slip and not posi trac. I may be incorrect with this, I haven't really paid any attention too much since ESP is there.

Well come to think of it, actually I have,, there is some slip between the traction of the left and right axels on these cars. It has to be to some degree.. hence the definiton of Limited slip.. It usually can't be felt that much because the ESP kick in but you can always tell by the rubber marks on the street.

Ratio has nothing to do with anything except that its the only difference between the rear end in the AMG cars of the same body style and the Non for example. There are no "special" rear ends for any version of any body style except in the final drive ratios.

velvet fog

Limited slip is the generic term for a locking differential. There are a couple of different styles. Posi Trac is a GM term and uses a spring loaded clutch to lock the axles when driving in a straight line and allow some slip when the car turns. Ford's Detroit Locker uses a spring loaded racheting gear set. Chrysler's name was Sure Grip. Even though I had a 1970 440 R/T Challenger with Sure Grip I don't know what scheme they used.

If you put the car on a lift in Neutral and spin one wheel, both wheels will turn in the same direction on a car with LSD. In Park, it is difficult to spin one wheel since the drive shaft locks up the entire mechanism. On a posi trac, you have to turn the tire hard enough to overcome the clutch drag.

Gear ratio has nothing to do with it.

newton22

Yes, on my Camaro, I can turn one rear wheel by hand and the other one will spin in the same direction.

I always thought MBs had open differentials (save for some AMGs), but ESP simulates an electronic limited slip.

velvet fog

You've got it!

my06clk

Not if the car is in park. right?

whoover

Why wouldn't it?

my06clk

One word.. Gears.

Its just not possible to have both axels turning the same direction and the force not be transmitted to the center Drive shaft.. There are no clutches here just gears.. something has to give or not give.. in this case if the car is in neutral, the drive shaft would turn.. If the car is in park.. then you are not turning both axels in the same direction. Sorry.. that's just not how any diff. works.. But I'm off that.. Let's just wait and see what Newton say's...

Here is some interesting reading to tag along with what I said earlier before about Mercedes differentials..

http://www.kleemann.dk/site/Main/accessories/lsd

newton22

Manual transmission.