E230 Auto - Overrun thump when I brake ?

[sophiedog]

Hi,
My pride and joy E230 Auto has only one problem. When I brake following a period of time on a straight road, the car seems to experience a thump like someone has bumped into my rear end. It seems to me as if the clutch orsomething isn't disengaging the drive on time.

Is this a common problem and can someone help me diagnose the problem.

Much obliged for any help.

 

[jaymanek]

sounds like your auto box may need a change of oil or may just be low.. Your car should have a red dipsick, so check the level while in neutral, car running on level ground.

Thanks

 

[grober]

You dont say what age your car is but the symptoms are indicative of something moving due to weight transfer under braking. Points towards rear subframe rubber mount problems or possibly worn differential mountings or even a worn/soft gearbox mounting.

 

[GarethM]

If the previous posts don't get to the bottom of the problem check the engine mounts.

 

[MBTECHNICIAN]

I would definatley check all of the above ideas first as they are good ones, definatley change the oil and filter, if you have not found nothing i would suggest that your auto gearbox (722.6) electric box) requires adjustment to the brake band B1 clearance these were a problem in all early electronic gearboxes and there was a modifcation for them,but also wear is a factor. when the gearbox changes from 2 to 1 the increased clearence in this brake band causes a increased filling time therefore especally when coming to a slow stop you would feel a bump as if almost from behind.to adjust this clearence the auto box would need to be completly stripped down and clutch disks checked/replaced and possilbly a bigger circlip which is used like a shim...
try reseting the adaptations of the auto box although if this is the case the fault will come back......
really you need to get it looked at by a professional weather it be a dealer or independant as it is hard to say what is wrong im am only trying to give you an educated guess

 

[sophiedog]

I'm so impressed with this forum. The car has covered 140,000 miles with a good service history. It runs very well.

The problem occurs when the car has almost come to a standstill under light braking, particularly coming off an off ramp on the motorway. It sometimes occurs when slowly stopping at traffic lights afetr a decent run in top gear.

I'll discuss your suggestions with my mechanic friend but I change the oil and filter regularly and can rule that one out.

That offered by MBTechnician describes it well so this could be the problem.

Is this a big time consuming job needing special tools? or could my usual general mechanic deal with it?


Much obliged.

 

[sophiedog]

Should have said that the car is a 1998 E230 Avantguard. 140,000 miles

 

[grober]

autobox specialist

I'm so impressed with this forum. The car has covered 140,000 miles with a good service history. It runs very well.

The problem occurs when the car has almost come to a standstill under light braking, particularly coming off an off ramp on the motorway. It sometimes occurs when slowly stopping at traffic lights afetr a decent run in top gear.

I'll discuss your suggestions with my mechanic friend but I change the oil and filter regularly and can rule that one out.

That offered by MBTechnician describes it well so this could be the problem.

Is this a big time consuming job needing special tools? or could my usual general mechanic deal with it?


Much obliged.

If the gearbox does need a strip down then its probably best left to an autobox specialist who is familiar with the 722.6 box. Someone who is prepared to offer a reasonable warranty after the repair. Be prepared for a big bill if its the gearbox! BUT get it checked by a MB dealer or specialist first as MBTechnician says.