Troubleshooting ASD, any experts? - PeachParts Mercedes-Benz Forum

Racekar · #1 07-28-2007, 10:12 AM

This may be long but I want to give all the facts I have.

95 E300D that I bought from a 10 year owner who had an independent MB specalist mantain it over the years. 162000mi in excelent shape. I have changed all the fluids and just replaced the rear brake pads. Here is my problem:
On take off the car seems very slow and lethargic untill about 15 mph and then it takes off. It's worse when going around a sharp turn, like you would make for a u- turn. Some times you can hear the inside tire scratching like it's sliding on the pavement.
I know that the ASD only controls the rear diff lockup untill about 15 mph, and that it can use the brakes if needed to control wheel slip. My ADS light does not come on during this time, but it comes on during the start up which is normal. I changed the fluid in the unit, which was very dark brown, and flushed the old stuff out of the lines. No change. I replaced the rear diff fluid, also black, but no change.
I think that the ASD unit has a problem and is trying to limit wheelspin that is not there and slowing down my takeoff. PO had all the brakes changed at the same time, the rear pads should never wear out before the fronts unless the ASD is causing them to work all the time? How do I check this out? ASD is electronicly controled with the ABS, yes? Is there a way to pull a fuse or something and shut down the ASD and see if it makes a difference? Any help would be appreciated.

yal · #2 07-28-2007, 04:23 PM

If the ASD light is not on then there is nothing wrong with the ASD system. The ASD system does not work with the ABS, they are separate systems.

They share the speed sensors on the front wheels and rear diff.

The ASD system does not use the brakes to create limited slip it instead uses a set of hydraulic actuated clutches inside the diff to transfer power between the two rear wheels.

If the ASD computer, using the diff speed sensor, senses a speed differential between the rear wheels it actuates a pump which actuates the clutches.

This is just a guess but the problem you are experiencing can be caused by a worn differential. The clutches in the diff allow a torque dependent locking effect, all the time and at any speed, of up to 35% independent of the ASD. It may be that they are binding when you make a u-turn, thats usually a classic sign of a worn diff.

Redline and GM sell a Limited Slip Friction Modifier you can add to the diff to see if that will help. Also make sure the oil you are using for the diff is limited slip compatible.

Also check to see if your half shafts are in good condition.

longshore1 · #3 08-06-2007, 06:54 PM

My ADS light just came on on the way home. seems to run fine. had the diff fluid changed a few months ago, and was told it looked fine. is there any harm in driving it a few hundred miles till I have a chance to get it looked at?

I don't see any fluid leaking, and the cruise control did not shut off when I tapped the breaks, I quess no more cruise control till I get it looked at. I've read that the gas engines have a "limp" mode. I suspect the diesel's do not have this mode.