Open Road

Hi
My name is Bill and I have a 1986 with automatic. The car rolls almost a foot when it is put in park. It also bangs into gear when you shift into park or reverse, or drive. The car had a lot of problems but is getting better. I have chased the vacuum leaks down and checked the vacuum modulator for proper operation. I thought I had lsd problems and went through the diff. Everything is tight in the rearend. The car shifts smoothly and doesnt slip. I would have to say that the transmission is sound. However it is annoying when you put into gear, and there is a significant clunk. Any ideas Thanks!

Bill,

These cars have a Mercedes transmission. The 'rolling' when put in park (on any kind of front/rear slope is characteristic of these transmissions (I've owned six 928's and 3 MB's built in the late 80's through mid 90's with these transmissions). A foot is a bit long, however. Have you actually measured the distance, or does it just 'feel like' a foot? I'd guess 2-4 inches is probably the 'normal' for them.

Gary

Well as far as the distance, I havent measured it exactly but when you put it in drive like I said before there is a significant engagement clunk. I have 600sl and it rolls a little bit but nothing like this.

Geez guys, I don't really remember any of my automatics rolling when put in park. It's been a while since I've had one, but I also always use the e-brake, so maybe I just never realized it before. I would be very concerned about the noise you describe, and would get the car somewhere where they know these transmissions.

It should be easy to see if the drive line slop is the transmission or elsewhere with the car on a lift.

OK so the car has been on the lift . The slop seems to be internal in the transmission. The drive line , the CV joints are all tight. I had just wondered if anyone had any experience with the internal working of the transmission and maybe the vacuum modulator. Roger at 928rus thought it was in the vacuum modulator and that I should do a vacuum leak down on it. I did and that doesnt seem to be the problem. However there were several vacuum leaks that have been repaired. Heater valve , AC in the dash, diaphragms and the spider in the V under the intake manifold all had leaks or were disconnected. Before I did this the car shifted Horribly, and now it is very smothe.

I assume that the transmission uses a park paw against a toothed ring or gear.
Either or both could be worn, or the rest would be what ever slop is leftover between the park paw and the output shaft.
Since it is a transaxle you get to add in any differential slop.
If you hold one wheel stopped, how much can you move the other?

What I know about automatic transmissions wouldn’t fill a postage stamp.

What keeps a car with an automatic transmission from rolling away all the time unless it’s on a perfectly level surface? It ain’t the resistance of compression of the cylinders in the engine because of the viscous coupled torque converter.

Parking pawl.

Is it possible that the PP is so bent/distorted/mutated that the transaxle’s guts can rotate quite a bit before it engages?

Here is a picture of the parking lock from the inside. You can only break it if you force it into P while the car is still rolling.

Does it click when it rolls, or does it just roll between two hard stop points?

It doesnt make any noise when it rolls ,but I know what your getting at. Per the pix it could make a clicking noise when it rolls past the segments on the ring. In any case it looks like a transmission out to repair. In any case it is a low priority project. Just finished the clutch change on Lamborghini, Ferrari needs new cats and Jag has a n alternator upgrade .