1989 300SEL transmission Vibration
 

I would appreciate any ideas regarding this vibration problem.
I have a 1989 300SEL with 121,000 miles. I changed the transmission fluid and filter about 25000 miles ago. The car shifts great and seems to run fine. I checked the transmission fluid level and it seems perfect.
About two months ago I started having a problem. When the car is stopped and in drive there is a fairly severe vibration coming from under the car in the area of the transmission. It actually sounds louder on the inside of the car then the outside. When the car is stopped in; park, neutral, or reverse the vibration is nonexistent.
Has anyone else ever had this problem? I do much of my own mechanical work, but I have to admit that I have no understanding of how an automatic transmission does what it does. Could it be the torque converter?
Appreciate any ideas.
Thanks!

there is a rubber and metal mount under the transmission...

could also be motor mounts if you feel the engine vibrating a bit.

transmission mount is about 20 bucks..maybe a bit more

Thanks for the reply Lee.

I forgot to mention that I replaced the motor mounts about 25000 miles ago as well. I did not replace that transmission mount you talked about. Is there any way to tell if its bad other then just replacing it to see if the vibration goes away?

For $ 21.25 and 1/2 hour of work, I'd replace it anyway. ;)

Good point Manny. I'll replace it and see what happens. I'll let you guys know the results.
Thanks for your help.

If its vibrating that bad, you should be able to tell with physical inspection by looking closely at it under the car (with the car parked and the engine off). Theres a large amount of rubber with the tranny mount that if its torn you should be able to tell. Theres also the driveshaft bearing and support although symptoms of this is usually vibration during acceleration.

The tranny mount is fairly easy to replace - 4 bottom bolts and one on top center.

I don't have a picture of the tranny mount (which I changed when I rpl the ds bearing and support but here's a pic of the bad ds support.)

http://i158.photobucket.com/albums/t...p1010163-1.jpg

There has been some transmission bel housing bolts come loose that will cause vibrations. I don't recall if it was at idle or at a particular road speed or condition. But checking to see if your nuts are tight shouldn't cost you much, unless you pay her :eek:

I had the same problem on my 90' 420 SEL until my mechanic changed all the motor and transmission mounts....what a difference. Before I changed them it was like sitting in a blender! When the mechanic showed me the mounts there was nothing left of them- like a carpenters dream- flat as a board.

Might be the exhaust pipe banging on the cross-member, the 300SE is notorious for this when the motor mount sags a bit. The torque of the engine when in gear would move the exhaust down closer to the cross-brace.
Easy to check, just turn left and accelerate, if it makes more noise than turning right, that's it. Or you can just look at it, there should be at least 1/4 inch clearance between the exhaust and the cross-brace (near the steering idler arm).

DG

Quote:

" I forgot to mention that I replaced the motor mounts about 25000 miles ago as well" .

Thanks for the additional thoughts fellas.
UPS delivered the transmission mount from mercedesShop today. I'm going to give it a go over the weekend. I'll post the result.
With a lot of help by researching some past posts on the forum I was able to successfully install a water pump and thermostate in my wifes 1998 ML320. This forum has helped me out countless times. I appreciate all the help.

I changed out the transmission mount on Saturday. It was an easy job for the do-it-yourselfer. All I needed for tools was; 13mm socket, 17mm socket and a 19mm combination wrench. I also used some PB Blaster on the top 19mm nut as it was a little stuck.
The old mount I removed was compressed what looked to be over an inch from the new mount. It also had a portion of the rubber giving way. It needed to be changed.
The new mount quieted the vibration considerably, but it’s still there. I obviously have some other issues.
I’m doing front and rear brake pads and rotors over the weekend. At that time, I’m going to check the bellhousing nuts, as was suggested, and see if for some reason a motor mount bolt has worked its way loose. The car idles just OK, there is no distinct miss at idle, but it does seem a little rough at about 700rpm I’ve had new; rotor, cap, wires, plugs, O2 sensor, injectors, and various rubber parts that may have caused a vacuum leak changed to improve idle. Whatever the case, the idle has been questionable for over a year, and this vibration issue is much more recent. I’m going to do a compression test asap to see if there is a larger issue behind the roughness.
Thanks again for your help. I appreciate any comments or thoughts.

Solution
 

I appreciate the help guys. I wanted to stick a fork in this post by providing the solution to my problem. In the end, the substantial vibration was caused by a collapsed motor mount. Lee, and others, provided the answer, but I had the blinders on and I refused to believe it. I had just replaced both motor mounts less then two years and 20,000 miles ago. I couldn’t believe that they had already failed. Well, the mount on the passenger side had collapsed to flat. Those were aftermarket mounts I purchased through Performance Products. They were out of warranty of course. I went to the dealer for the new set. Hopefully they will hold up better.
I can’t believe the mount failed in such a short time. At least it was a learning experience for me.