Internal Thump 1987 420 SEL

[wscheffer]

I have recently purchased a 1987 420 SEL and being my first MB please forgive me if I ask a stupid question. The problem is that after the car warms up it will down shift hard with an internal thump sound coming from the backend. It does this around five mph or less. I don’t think that this is the normal operation of the vehicle and when I had it on the rack my mechanic and I checked the bushings that connect the drive shaft to the transmission and differential and these appear to be fine. Does any one have a suggestion as to what might be causing this!

 

[GEORGEROV]

I would check the differential upper support mounting is not shot.

 

[television]

Normally your fault is a vacuam line off, on the gear box.

http://www.detali.ru/cat/oem_mb2.as...706&VIN=*&CT=GA&cat=14P&SID=27&SGR=195&SGN=09

malcolm

 

[Mikesmerc]

As Malcolm says this vacuum line can make a huge difference, had a diesel 123series with this disconnected and it made for neck snapping changes. Also gave poor changes on my 560sec when a backfire blew it off.
Mike

 

[wscheffer]

Result of Internal Thump

I finally got up the courage to take the 420 to the MB Dealer and tried to hang onto my wallet. Besides the usual fluid and filter change and changing of flex disks. The MB Dealer said it also needs a new modulation valve and the B2 band in the servo needs to be adjusted. And the killer is the MB Dealer can do these simple repairs for only $1,400 dollars. WOW!!! Thanks to everyone that posted to this question it really helped.