I have a 88 420sel with 119000miles on it, and going from park or neutral to drive or rev. there is a fairly loud clunk similar to excessive lash on a old chevy PU with a milliom miles on it. This is embarrassing for a nice looking benz as your backing out of a crowded parking lot However there is no noise down the road or ever again until you shift out of drive into rev. or the other way. It also seems to bang coming out of rev. too, but not pulling it out of drive. Absolutely smooth and quiet down the road and when the auto shifts, positive shifts and no abnormal noises. Could someone please help with a couple of suggestions. Have also changed the gear oil recently, just as maintenance, and no change.

Front flex disk is the most likely cause, but you also need to check the pinion for excessive "lash" -- usually not the ring and pinion gear, but instead the carrier for the "spider" gears in the differential. The bearing for the shaft wears oval, and it makes a terrible clank.

Take a look -- if the flex disk has cracks in it, replace it. If the driveshaft turns a half turn or so and makes the clunk in the diff, you need to have it checked, might be time for a replacement.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I agree with Peter, but do not wait on checking or replacing the flex disk. If it totally fails while driving it is a major disaster.
Ed

Had it checked out at a MB shop and they found the Idle vacuum control was bad causing the idle to stay up at 1000rpm after it warmed up, now idles at abaout 700-750 always. It doesn't clunk going into drive at all, but still does it going into reverse, and bangs hard coming out of reverse, like it's stuck in rev. gear a little. They said it was probably the reverse clutches being worn causing the piston to have to travel further to engage them and it picks up speed while doing this and causes the extra banging into reverse. Does this sound like the probable cause or might it be something else? Thanks, EM

Oh, I forgot to put in the previous reply that they did check the flex disc's and said they were fine. Sorry I forgot that part.:p
EM

Low vac on the transmission modulator may do that. I'd also check the transmission mount and the shift control cable.

Worn band will cause rough shifts sometimes as the servos can be out of synch if one is late.

I'd still check the differential for excess play.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!