V12 Uber Alles, Replacing the Rear Window Regulator in a W140 Mercedes Benz

Replacing the Rear Window Regulator

Pete's Note...As a W140 owner, you know that the windows in these cars are very heavy due the dual-pane design. While they help provide a luxuriously quiet ride, the weight of the windows puts a strain on the motor and mechanism that drives them up and down.

An article written and kindly provided by Simon Claringbold

Rear window regulator failure is common in W140s. When the rear window was being raised I heard a popping noise, no more raise action. I could hear the motor attempting to wind but no movement. I was able to force the window up by hand by pressing on the glass and lifting. On enquiring about the part number from my local independent parts supplier I was told that the original part had been superseded three times. Hopefully, with improvements each time.

The regulator itself is side specific. The regulator consists of a frame, slider, cable and pulley for pulling up and cable and pulley for pulling down. Cables wind into a common spool. The electric motor bolts onto the spool surround and drives the spool. The spool is designed to store the exact length of cable required from the raise/lower operation. If the cable separates from the regulator slider, the excess cable is wound into the spool creating a jam.

Remove rear door trim. Pry out the plastic block in the arm rest. Remove screw. This is the biggest screw. It must be fully removed. Pry out, from the rear, the electric rear seat adjustment switch panel, unplug wires and store panel. Panel opening reveals 2 screws, remove these. Unscrew plastic door latch surround – one screw. Carefully lever off door trim. If you start near the latch looking as you go you can carefully lever out each clip. HOWEVER – NOTE closest clip to the latch is different!
The clips away from the latch pry off. The clip near the latch LIFTS off.
Once all clips are out, lift the door trim off starting at rear of door. Lift trim up away from door. Unplug wires for electric window, lighter, courtesy light. Metal connecting rod for door latch handle also unclips. Remove door trim. At this point it is easy, working from inside the door trim to remove the ashtray and courtesy light. This will allow easier refitting of the door trim. Remove the door speaker – 3 smaller screws. Carefully remove dust sealing from around door. This pulls away from the edges with a bit of work but is possible.
Door trim removed, dust seal pulled away from edges. The dust seal adhesive was still sticky and reusable even though the car is over 10 years old. Remove the window motor – 3 by Torx size 24 bolts. The winder motor unit can be pried off the old regulator. Lower the window by hand until the slider becomes visible – I’m assuming the raising cable has broken here. There is a black clip that must be removed to allow the window to be disengaged from the regulator slider.
There are 5 rivets holding the regulator onto the door. You must drill the rivets out. Go easy, ideally you should just drill the rivet metal only, not the door metal – you don’t want to make the rivet holes bigger. STOP!! Make sure you just remove the rivets for the regulator – there are other rivets in the door that you want to leave there! The regulator rivets hold ONLY the regulator. The regulator also has tabs at the top, bottom and centre, that engage in slots in the door. Jiggle the regulator around once you have these tabs disengaged, then you can remove the regulator through the door aperture. The window can be pushed up by hand to allow more room. The original regulator had a plastic slider into which the cables are embedded.
Old regulator in pieces, window motor above is fastened to the regulator with 2 Torx head bolts. Note the blue slider, window raise cable had pulled away from the plastic slider.
Fitting the new regulator New vs Old. Broken plastic slider where the cable pulled away. Top is the new regulator with metal slider in which the cables are embedded
I used bolts and nuts instead of large rivets to fix the new regulator. Position the slider at the halfway point. Get new regulator roughly in place, lower window by hand and engage window with the regulator slider and replace retention clip.
Engage regulator tabs in door slots and fit the 5 nuts and bolts – or 5 new large rivets.
Refit the motor with the 3 torx bolts. Fit window motor control wires – one round plug and one square plug. The operation of the window can now be tested using the drivers console switch. If working, proceed.
Refit door dust proofing, make sure you have ALL the wires coming out through the aperture in the dust seal. Refit the speaker and reconnect plug.
Position trim near enough to the door to refit door latch metal rod connector, pass wires out though their respective apertures in the door trim.
At this point it is easiest to plug in the connector for the window raise/lower button.
Align door lock button on door trim and place just the top of the door trim onto the door. Working around the door, align the various clips noting that the one closet to the latch has to go on before the trim is moved down to its home position. Push door trim clips into their engaged position around door.
Refit door latch trim with small screw. Refit the 3 large screws, the largest of which goes into the vertical rear most position. Cover large screw head with plastic block.
Plug in ash tray, fit in at bottom and push top home.
Plug in rear seat and headrest connectors, engage front of trim and push home rear of trim.
Plug in courtesy light. Light is mounted with the plug closest to the front of the vehicle, push home rear.
I lubed the window track using graphite powder. The W140 ‘L’ rear window is a large and heavy window, the motor audibly strains much harder when lifting the window as opposed to dropping the window.
I found the job to be straight forward. The above is based on my personal experience fixing my own vehicle. The information is supplied with no warranty or guarantee. I am not a qualified mechanic. If you are not confident following this procedure take your vehicle to a registered mechanic. Regards, Simon Claringbold

Thanks go to Simon for this fine write up!

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