Violent auto gear change

[Scottish_lad]

I have a problem with automatic gearbox on my 1995 Mercedes C220.

There is a loud thumping sound from the back axle when the car automatically changes gear. It seems to vary in intensity at different engine speeds. One garage has suggested that it might be caused by worn sub frame bushes at the rear. I think it may be something else. It feels like a gear change with really bad clutch control, so is the problem in the gearbox?

I would appreciate any suggestions.

Thanks

 

[wireman]

Your prop shaft has rubber couplings, these fail and give the symptoms you describe. There are many rubber bushes in the rear suspension and these may also be responsible.
Have you checked the transmission fluid level? auto boxes do funny things when its not spot on.

 

[television]

Just to add to Wiremans post, do check that the vacuum system on the box is all connected up, is leaks here make lumpy changes

 

[Parrot of Doom]

Check the doughnuts on the propshaft for cracks. From what I've read replacement isn't an expensive or big job. They look like this:

You sometimes have to remove them to check their condition. They do have the ability to fly apart with startling results....

Fortunately that little mishap was fully repaired (it isn't my car!)

http://dieselgiant.com/Mercedes flex disc failure.htm

 

[wireman]

Cor whada mess, I thought mine was bad when just the rubber bit blew up.

 

[Scottish_lad]

Thanks for all the advice.

SOLVED THE PROBLEM. It was a little white vacuum pipe that goes from the top of the gearbox to the manifold. The tube was off the top of the gearbox. Put it back into the rubber socket...and hey presto....no thumping. Everything back to normal. Thanks everyone.

 

[television]

Always handy to remember that hard changes on the 722.3,4,5 are mainly vacuum problems

Thanks for posting back with a good result