I guess the obivous cause for this might be worn teeth on the window regulators. OTOH I recall in an auto electronics CC course I took years ago that there was a way to adjust wiring or a sensor (many years ago) so that the window stopped in the right place. That might have been Detroit cars, not sure. I know most of them have some sort of sensor so the damned blunt glass edged guillotines don't sever children's fingers, etc.

I'm searching for a vacuum leak, the yellow line under the hood near the firewall indicates that there is no leak in the line up to the front door or the actuator therein. Also no leak in the storage egg carton in the trunk. The turn off swith works fairly well except when I unhook those two connections so I'm guessing reservoir vacuum is powering that but it tends to indicate there is no problem in that circuit though I'll check it further. I've already checked the pump and brake booster diaphram and they are sound.

I bought Kent's little $20 dollar 'Diesel Vacuum Source Troubleshooting and Repair' manual and it's full of good info. I'm confident I'm going to get this working. The windows I'm not so sure about.

Aside from weak brake assist, the worst performer here is door locks, leading me to think one or more doors has an issue. As I'll be making them naked, now would be a good time to look at the window noise. I have exactly no experience with MB windows so here I am. I suspect some of you have.

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1986 300SDL, 362K
1984 300D, 138K

You should have another smaller vacuum reservoir inside the rear portion of the left front fender behind the wheel well valance. Also a check-valve on - if I remember correctly - the yellow vacuum line just behind the speedometer. Both are possible leak sources.

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Don't Chrome them; polish them

The windows have no "stop" switch, which is part of the problem. You may find you have a crack or two inside the door where the window regulator mounts to it.

There is something inside of the window motor if I found the right picture where there something that us supposed to stop the window motor when there is resistance. The yellow arrow points to it.

On the rear windows one of the reasons the gear teeth get badly worn is the pot metal part of the Window Regulator bends.

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the responses. I'll look into all of that. The yellow check valve seems to be good but I didn't know about the second reservoir up front.

Good tip on cracks in the door, I'll look for that. If that is going on, might be some way to firm them up. Maybe the lowest MIG setting I have would sort of re-attach those pieces, assumimg it's an appropriate spot to weld.

I thought there would be some safety cutoff mechanism in the switch. I was curious about the history of that, I of course know about the business of serious injuries to the hands and even heads of children playing with power windows, including an unknown number of deaths. My reading so far indicates that the safety thing reverses the direction of the window, sometimes opening it completely. That's not what I want here of course.

How Does the Power Windows Anti-Pinch Safety Feature Work?

The driver's window closes just fine, it's full open where it makes noise. It goes down a tad too far and bangs something in the process. So far it comes back up just fine but I'd like to fix that, could lead to grief in future otherwise.

The rear windows are suddenly reacting to long non-use. One doesn't move at all, the other quite slowly. I seem to recall that it was also at full open those made noise but suddenly I'm hazy on it. I had a similar problem of not moving at all with the rear windows in a cherry E30 I found about 7 years ago. An elderly couple had owned it, it sat in a garage for about 2 years. Something gets sluggish, can't remember exactly what got those windows working on the BMW. They say memory's the second thing to go, I forget what the first one is.

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1986 300SDL, 362K
1984 300D, 138K

Maybe I'm wrong about there being no stop sensor, but I've seen several 123 owners talk about how they have a procedure for rolling up the windows that involves stopping right near the top and then gently easing it closed so it doesn't bang and cause damage. Pretty sure you can use it to chop vegetables as well.

As for cracks where the regulator bolts up, I welded mine up and they've been fine (been using "the procedure" as well for good measure). You can also lube everything while you're in there.

Good advice. I may just need to live with some of this. But I'll see what I can fix.

On the vacuum issue, I was pleased to learn that the individual vacuum actuators for each door are not only available, they are $20 apiece at Pelican. Dang ... Don't know if I need any yet but nice to know.

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1986 300SDL, 362K
1984 300D, 138K

I'd be very surprised if the W123 has external sensors of any kind in the window mechanism. There is a component in the motor which I assumed to be a capacitor but didn't dig deeper than that, it could be a current limiting device which would in theory stop the window if it's blocked. On a W126, there is a hard stop for full down, it's somewhat adjustable. For full up, it's all about paying attention.

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

I did not believe there was anything that acted as a window stop on the W123 Motors either till I saw it on someones thread and later when I took my Window Motor apart.

My Memory is extremely hazy but what I remember is it is a bi-metallic arm with a contact point and an opposing contact point. The contacts make contact till the bi-metallic part gets hot enough to pull that arm and contact away from the other contact point and opens the circuit stopping the window movement.

Since both of the back windows regulators on mine had bent pot metal parts and one had gear teeth worn so severe I replace it with a new one. In practice the bi-metallic switch thing does not work well. It does stop the window but stresses the mechanism.

People don't seem to have the same issue with the front ones.

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84 300D, 82 Volvo 244Gl Diesel

Now that makes sense. I see the word "sensor" and think absolute position sensing, either with an encoder or limit switches, which would stop the window in predefined positions. Didn't occur to me that it could mean an over current device, which in fact does sense what's going on.

I'm thinking you are right, there are 2 large coils plus the square thing in the brush end of the motor. I decided it was for RF suppression but then I've never seen something that complicated for RF suppression, it's usually a ceramic cap across the motor leads. It's very possible that the coils act as heaters and the square thing is a thermal overload or thermal fuse. A stalled or sluggish motor may not pull enough current to pop a fuse but should trip it's own built-in overload. As you say, it probably doesn't protect the mechanism all that well but may be more about preventing fire.

I learned something today.

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

I think the freaking out over children losing fingers reached into the thinking of all automakers. They wanted to keep the power windows. This isn't exactly that but it's similar, some of it may have had that as a secondary aim.

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1986 300SDL, 362K
1984 300D, 138K