help rear window (coupe) only rolls down half way - Page 2 - PeachParts Mercedes-Benz Forum

5cylinder · #16 12-24-2020, 09:18 AM

Quote:

Originally Posted by 87tdwagen

Without going into the details regarding voltage drop and electrical corrosion, maybe we can agree on 2 key take aways:
1 The further current has to travel, the more loss there is, and
2 Everything exposed to air, corrodes, well except gold.

This is not specific to the W123, it applies to many makes, models and years. Many window motor systems route thier current through the switches. In short runs, with the switch on the door, this usually is not an issue. But, in console mounted switches, the wiring could easily be 10x the length of a door mounted wiring, and the current loss is reflected at the motor. Needless to say, burnt switch contacts are a undesirable consequence of routing the power through the switch.

The very same principles that apply to adding control relays to headlights apply to window motors, they also draw significant current and will respond the same way. If relays can deliver 100% power to your lamps vs 75% prior, you can also upgrade your 75% performance window motor to 100%, enjoy the new zippiness and never deal with burnt switches again.

Electrical corrosion can be very difficult to see with the naked eye at times, but it is there, it started the day the wire was made. Insulation coatings often dont give it away, as it lays underneath, sometimes very visible and yet surprisingly as the insulation provided no clue. It has been my experience that age and current load resulting in corrosion, reveal measurable resistance increases causing many electrical gremlins. It's just been my policy on these older cars to add control relays wherever I needed dependability.

Hope that helps clarify my 2 cents

An interesting read, thanks for sharing all of the additional information. Always fun to learn new things.

Good points. The appropriate relays are centainly inexpensive enough. The labor is always where the real work is hiding although researching and then drafting a good quality schematic and doing good planning for the project is plenty of work, too. There just might be another relay project in my future! Thanks again-

vwnate1 · #17 12-27-2020, 07:12 PM

This was a design defect from new, that they began working slower and slower before stopping 1/2 way indicates they began to drag and this is what causes the lift to bend, I have the M-B factory replacement lifts and they bend too unless you take it all the way apart and clean and lubricate to as-new condition .

Yes, relays are good but not necessary here .

You'd have to have owned or worked on, a W123 Coupe to understand .

There's a really detailed thread in here some where that has good photos of all the many steps necessary to make a good job of this .

5cylinder · #18 12-27-2020, 07:29 PM

Quote:

Originally Posted by vwnate1

...take it all the way apart and clean and lubricate to as-new condition.

This is exceedingly good advice vis-a-vis these lifts. And, for this particular undertaking, I suggest only using the legendary M-B Gleitpaste.

Quote:

Originally Posted by vwnate1

Yes, relays are good but not necessary here.

I do tend to agree.

Quote:

Originally Posted by vwnate1

You'd have to have owned or worked on, a W123 Coupe to understand.

Now, THIS, is poetic truth, LOL. The lift situation in the coupe ain't a pretty picture in the least once the panel is off.

vwnate1 · #19 12-27-2020, 08:28 PM

Only those who own or have worked on understand this particular problem .

A few years back I encountered a decent junked 1984 300CD, it had brandy new M-B 1.4 window lifts, they'd foolishly slapped them both in and the driver's side one had begun to bend .

I bought both but m thinking of selling my coupe on so the lifts will be extra after it's sold .