Power window 'clunks' at end of travel - PeachParts Mercedes-Benz Forum

Hatterasguy · #1 10-25-2005, 10:53 PM

Mine did the same thing just before this part broke:
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1MB12FET61N91D13MR&year=1987&make=MB&model=300-SDL-001&category=O&part=Window+Regulator+Kit

Pretty simple fix.

unkl300d · #2 10-26-2005, 12:26 AM

My 300SE had that prob and it turned out to be both the window regulator teeth and the sheet metal onto which the regulator bolts onto was bending. The sheet metal fatigue seems to be common on the Se's.

Same car's rear driver side window would not lower with motor, That turned out to be just the plastic bushing referred to by the previous poster.
Anyway, symptoms have diff incarnations.
Take the panel off and snoop.

Den

andmoon · #3 10-26-2005, 03:19 AM

My sheetmetal actually cracked. JB weld and a piece of scrap metal to the rescue. Stiffening the sheet metal was enough to stop the gear teeth from jumping although it was worn quite a bit.

lkchris · #4 10-26-2005, 05:52 PM

Quote:

Originally Posted by andmoon

My sheetmetal actually cracked. JB weld and a piece of scrap metal to the rescue. Stiffening the sheet metal was enough to stop the gear teeth from jumping although it was worn quite a bit.

Would think sheet metal "cracking" is symptom and not the disease.

Disease is probaby misadjustment or something else causing hard running, which then stresses the mounts.

autozen · #5 10-27-2005, 10:23 AM

There are no adjustments on an MB sedan window except the lower stop and that should be easy to figure out even by the dumbest window putter inner. The regulator mounting holes can enlarge and the metal can crack if the bolts come loose and the window is continuously operated in that condition. The biggest cause of power window mechanism failures on MBs is the regulator. The teeth at the end get ground down and or the regulator gets twisted way out of shape. Some regulators just suffer from fatigue, but most fail, because idiots keep their finger on the switch in hopes the window will go a couple of feet higher or lower. Those motors are very powerful, and if you keep your finger on the button after the window has reached the stops, it will continue to apply force to that regulator. Since the window can't go anywhere, the force grinds on the teeth and causes the regulator to twist sideways. When you hold your finger on the button in the other direction, the regulator twists in the other direction. Soon it binds up and won't move at all. Having witnessed these failures on hundreds of regulators I have replaced for clients, I take my finger off the button as soon as the window has reached its destination and don't need to replace any regulators in my MBs. My 83 wagon has 355,000 on the clock with same driver's window. Hope this sheads some light.

donbryce · #6 10-27-2005, 06:00 PM

It was the gear teeth at the end of the regulator quadrant. As the first picture shows, 4 of them had become distorted and lost metal from the main drive gear grinding on them at the end of the windows travel. The 'clunk' I was hearing would have been the last revolution of the drive gear skipping over these teeth.
Since I'm a stubborn person when it comes to replacing things, I decided to mig-weld-fill the bad teeth and cut new ones. First step was to hammer everything flat on an anvil, then wire wheel off the cadmium plating in the area. I welded the section until it was filled, then ground both sides flat again.
A 3/4" wide half round file proved a perfect fit in the good teeth. I sprayed the area with machinists blue dye, made a cardboard pattern from the good teeth, then scribed the outline for filing. Cutting was done with a thin grinder cut-off disc and the 1/2 round file, finishing with a small needle file to trim the detail. Picture 2 shows the re-worked area.
I have no idea why Mercedes made this piece out of soft, 1/8" thick steel. I'm sure my welds are tougher than this metal was.
Also, I'm not sure why this happened, as I'm careful to not keep my finger on the button when the window is up (wife may have done this, but I doubt it, since the window stays up most of the time for the A/C). It could be that 20 years of use have just taken their toll and it just plain wore out from metal fatigue.
It now works good, not perfect, as it kind of judders halfway up, as if sticking on the sides. I sprayed silicone into the side tracks, but it didn't help. However, it goes up without any 'clunk', and goes down smooth as, well, glass.
My thanks to all again for the input. All the mounting bolts were tight, and for some reason, my model doesn't appear to have the down-stop adjustment pictured in the MB manual. That wasn't my issue anyway, but I thought I'd mention this, since someone might suggest adjusting to stop the juddering.