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1994 S320 W140 Front Seat Lumbar Support

6877 Views 8 Replies 7 Participants Last post by  ppp111
The front seats both have pneumatic lumbar support operated by a dial on the door sides of each seat.

My problem is that the lumbar supports seem to have a mind of their own. They inflat without being asked. If I set the dial to 0 this deflats the lumbar support. But then the lumbar support decides to squeal.

I'm reluctant to disassemble the seat without some understanding of the mechanism first. Can't find any source of manuals anywhere.

Are the two front seat lumbar supports connected at all, I first thought that only the drivers one was defective, I've now been told the passenger one also inflats without being asked. But it does not squeal.

If the dial is set to 0, setting it to something between 0 and 5 does seem to correctly inflat the lumbar support.

Any assistance would be greatly appreciated.
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· Registered
W140 S class, E31 850Ci, XC90 Exec AWD geartronic
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444 Posts
you have a vacuum leak.

It could be from any of the below

* Either one of the bags in the front seats
* The vacuum hose connecters under the front seats
* The vacuum connectors under the rear bench leading into the ZF pump
* or a defective ZF pump($$$$$)

My guess is that the pump in trying to maintain pressure inside the front lumbar bags. As its leaking away the pump detects pressure loss and refills the seats.
If there is a vacuum leak on any of the seats, both will malfunction. They are connected to the same line and operated by the same relay in the ZF pump. Check these lines 1st. The are easily distinguished by their grey colour .There are three lines in all. Two are vacuum - and draw vacuum, the other line is vacuum + and pumps air into the seats.

My ZF pump was recently replaced. the front lumbar support was the first device to fail.
[|)]
 

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90 300 SE ,85 300 GD
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1,570 Posts
Over Eager Car Detailers

In an effort to "clean" under the seats the tube was jerked loose on my passenger's seat. Perhaps that is the problem. I no longer have the interior "detailed" by anyone except myself!
 

· Registered
W140 S class, E31 850Ci, XC90 Exec AWD geartronic
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444 Posts
wise move.
Detailers, most mechanics included, dont give a sh!t about your car and rush t...


wise move.
Detailers, most mechanics included, dont give a sh!t about your car and rush to finish the job. I like to watch or check up on them whenever my car is being worked on.
Cleaning is only ever done my me.
My car has just gone onto the shop for a transmission overhaul and front engine gasket replacement (M104). No doubt, I'll be stopping in to check the progress
[;)]
 

· Premium Member
2015 C300W4; 2007 E350 W211; 1992 300SE W140
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132 Posts
I have a problem with only the driver side support. The passenger side seems to be fine. Does anyone have a diagram or advice that they can share? The only thing that is not working is the drivers side lumbar support. it is not inflating.
 

· Registered
140 600 1991
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221 Posts
By the way -
do you know how to get to the "0-5" switch to check/clean it (if can be cleaned at all)?
On the driver side it feels like not responding till in "0-4" position and then towards 5 it inflates very well.
Probably there is a way to remove this plastic side cover.
(W140 1991)
 

· Registered
1986 C126 560SEC & 2003 W203 200K Wagon
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154 Posts
I have a problem with both the seats. After removing the bench seat and revealing the pump, did some checking and heard air escaping the drivers seat.. I think I would need a new bladder.

As for the front passenger seat, nothing was heard and it does not operate and any level (0-5)

Will have to look into this once I have sorted out the front driver and passenger doors locks, which may have a slight leak as well.
 

· Registered
S600L, 500CL, 560SL
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110 Posts
By the way -
do you know how to get to the "0-5" switch to check/clean it (if can be cleaned at all)?
On the driver side it feels like not responding till in "0-4" position and then towards 5 it inflates very well.
Probably there is a way to remove this plastic side cover.
(W140 1991)
Take the Side cover of the seat which holds the adjuster switch off. Then from inside of the seat cover the switch can be taken out n cleaned. Be careful not to brake the two tabs in front of the seat cover.
 

· Registered
140 600 1991
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221 Posts
Thanks for this hint. But where to start in order to not brake things (back, front, bottom...?).
Maybe you know? - in two sentences...
And did you go throught that? Can the switch be dismantled for cleaning?
 
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