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Old 02-03-2006, 09:39 AM
Registered User
Join Date: May 2001
Posts: 161
W140 drivers seat adjust

My 1995 S420 drivers seat will not adjust (up and down) with me sitting in the seat..... It will move up and down if I'm standing outside and adjust the seat before sitting down.

Has anyone solved the W140 seat problems that were caused by broken plastic gear parts? Replacement for the commonly broken gears were not availble 2 years ago when I purchased the car from a MB dealer. At that time the seat mechanism was replaced by the dealer prior to my buying the car. This replacement is now having the same trouble as the first one.

Any advise or knowledge will be appreciated.

Did anyone consider getting spare parts hand made by a machinist, and have extras left over ?


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Old 02-07-2006, 05:06 PM
Registered User
Join Date: May 2001
Posts: 161
140 seat adjust problems

Bump it up to the top again, Am I the only MB owner that has had 2 of these seat malfunctions. Let me hear what you did to correct similar troubles?? (95 S420)

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Old 02-08-2006, 06:45 PM
A. Rosich's Avatar
Registered User
Join Date: Nov 1999
Posts: 883
The front passenger seat on my S 500 L behaved erratically for a while. I unplugged all connections at the bottom of the seat, blew compressed air on them and re-attached them firmly.

It cured all the problems completely.

I have read of other members doing the same thing to the switch on the door.
A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]
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Old 02-08-2006, 07:46 PM
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Join Date: May 2001
Posts: 161
Thanks for the suggestion.....

It should be worth a try-- certainly won't hurt to give it a shot. On the first seat which broke prior to my purchase I don't believe it was electrical at all... I saw the seat fall loudly (about 3 inches) with a rather large, heavy salesman in the driver's seat as he was showing me the car.

Does anyone know what mechanism tells the electric motor that the seat has reached the top (or bottom) of travel and cuts the power rather than allowing the motor to just choke down as it reaches the limits of travel??

It appears that the motor falsely thinks the limit of travel has been reached and cuts off because of my 170lb weight being added to the seat. Without my weight it continues on up to normal height. ?? Why, I don't weight enough to trigger an end of travel cut off.

Any one else have an idea?

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Old 02-09-2006, 01:34 PM
Registered User
Join Date: Jan 2006
Location: Central PA
Posts: 49
I'm not speaking with broad MB experience.

With you in the seat the motor draws much more current. There could be a marginal electrical connection to the motor. At low current flow (unloaded seat) there is little voltage drop across this marginal connection. With the seat loaded current flow increases and the voltage drop across the connection is great enough that there isn't enough voltage across the motor.

Find what connections you can. Before disconnecting them inspect them to see if they are visually seated properly. Then diconnect them and inspect the contacts for arcing. Also, make sure the contacts are clean.

Maybe you'll get lucky.

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