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

mushedroom · #1 10-19-2006, 01:53 PM

hey everyone

i have a 1984 300cd (coupe) turbo diesel (w123)
and this is my weird window story...

i had a dead front panel switch for the rear driverside window, but reaching over and pushing the rear panel button always worked in getting the window down and up.

this morning before going to work i replaced the front panel double switch.

now the rear window only goes down half way.
!!!FRUSTRATING!!!

SO thinking it might be the switch i replaced the old switch with the original one and tried to lower and raise the window using the rear panel switch...
I LOST THAT ABILITY...NOW THE REAR SWITCH ONLY MAKES THE WINDOW GO DOWN HALF WAY!!!

and furthermore....
the window doesn't fully close so i have to manually grab and pull the rear window up so that it gets a proper seal/connection with the front driver window....
ugh

HEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEELP!

Johnhef · #2 10-19-2006, 01:56 PM

more than likely your regulators are bent and dry aside from your switch problems. take the switches apart and clean all the contacts, thats the easy part.

I just went though all of this on my 82 coupe last spring after getting tired of 2 years of not having functioning rear windows in the summertime. once you get the switches working right, I can help you with the rest of it.

mushedroom · #3 10-19-2006, 01:57 PM

Quote:

Originally Posted by Johnhef

more than likely your regulators are bent and dry aside from your switch problems. take the switches apart and clean all the contacts, thats the easy part.

I just went though all of this on my 82 coupe last spring after getting tired of 2 years of not having functioning rear windows in the summertime. once you get the switches working right, I can help you with the rest of it.

the new switch is brand new

Johnhef · #4 10-19-2006, 02:01 PM

rear and console switches are both new?

swap left and right sides and report back.

mushedroom · #5 10-19-2006, 02:05 PM

no rear is original (but never had a problem with rear before)

ok
i'll swap the right front switch (working no problem) with the new left front switch and report back

question:

so the new switch...using it the rear window started to go down SUPER SLOW and initially on the first run, didn't even want to go half way...
then after 3 or 4 times switching up and down it finally went down a few more inches to the half way mark (more like 2/3 of hte way down...

i thought if i put the car back to the way it was (old front switch replaced) that for sure the rear button would work like it did before....

any technical theory on why now nothing works like before?
i'm almost certain it's switch related.

vstech · #6 10-19-2006, 02:09 PM

it really sounds like the window has gotten out of it's groove, or the regulator is mis-aligned. honestly, it sounds just coincadentally that it happened at the same time as your switch problem.
John

mushedroom · #7 10-19-2006, 03:06 PM

ok
well i'm going to do the front switch, switch to see if the button works...
and i will report back.

KCM · #8 10-19-2006, 05:49 PM

I bet the bracket that attaches to the glass and to which the regulator arm connects to is bent. My car did the same thing when I got it. I had to take the window out and bend the bracket back into shape. Later I found out that Mercedes evidently made a change to the part later on and welded in a reinforcement strut to prevent the bending. This was evidently a design flaw. Probably just a coincidence that you were working on the switches.

Or, one of the window adjustments came loose and is causing the window to bind.

CostaRica 300CD · #9 10-21-2006, 07:27 PM

My mechanic told me that I need to replace the regulators on my rear (slow opening and not closing all the way) window on my '82 300cd coupe. I'm having a hard time locating these items, any suggetions on where I can find them?

jtbenzman1 · #10 02-21-2012, 10:06 AM

Often all moving parts of need to be lubricated

math · #11 12-22-2020, 03:24 PM

Here's a video guide/fix on how to solve the slow to go up/down as well as only going half way down in the w123 coupe rear window

https://www.youtube.com/watch?v=FkQnqI80kPo&ab_channel=qwertyui90qwertyui90

87tdwagen · #12 12-23-2020, 07:50 AM

I know this is an old thread, but have read so many of these that I thought it would be worth mentioning. Many of these cars are 30+ years old, most likely have their original wiring still in use. Do yourselves a favor and add control relays to your major components, headlights, windows, power seats etc. You have wiring corrosion simply from age and use that adds a lot of resistance to a system that was at best marginal when new.

Take for example the rear windows in this case, the current travels from the battery, through the font switches, through the back switches, and eventually to the window motor, I would hazard a guess of anywhere from 3-5 meters of wiring before hitting the motor....all of that wiring with corrosion that you can't see, is going to result in a major voltage drop along the way.

Add control relays to power the windows from a short run of power from a terminal bus, and use the factory wiring to send the trigger signal to the relay, no more burned out contacts in switches, no more slow motors and given the low current going through the modified factory wiring, it will be trouble free for many more years to come.

math · #13 12-23-2020, 08:25 PM

Quote:

Originally Posted by 87tdwagen

I know this is an old thread, but have read so many of these that I thought it would be worth mentioning. Many of these cars are 30+ years old, most likely have their original wiring still in use. Do yourselves a favor and add control relays to your major components, headlights, windows, power seats etc. You have wiring corrosion simply from age and use that adds a lot of resistance to a system that was at best marginal when new.

Take for example the rear windows in this case, the current travels from the battery, through the font switches, through the back switches, and eventually to the window motor, I would hazard a guess of anywhere from 3-5 meters of wiring before hitting the motor....all of that wiring with corrosion that you can't see, is going to result in a major voltage drop along the way.

Add control relays to power the windows from a short run of power from a terminal bus, and use the factory wiring to send the trigger signal to the relay, no more burned out contacts in switches, no more slow motors and given the low current going through the modified factory wiring, it will be trouble free for many more years to come.

Seems like an odd thing to do, why not just replace the bad wires when/as needed ?

After lubricating the tracks/guides the window is much faster going up and down and both rear windows are exactly the same speed which tells me they are running well

( unlikely that both degrade to exactly the same point (s) )

I believe that unless you live in a corrossive salt filled wet environment, you won't have that issue.

5cylinder · #14 12-23-2020, 08:56 PM

Quote:

Originally Posted by 87tdwagen

I know this is an old thread, but have read so many of these that I thought it would be worth mentioning. Many of these cars are 30+ years old, most likely have their original wiring still in use. Do yourselves a favor and add control relays to your major components, headlights, windows, power seats etc. You have wiring corrosion simply from age and use that adds a lot of resistance to a system that was at best marginal when new.

Take for example the rear windows in this case, the current travels from the battery, through the font switches, through the back switches, and eventually to the window motor, I would hazard a guess of anywhere from 3-5 meters of wiring before hitting the motor....all of that wiring with corrosion that you can't see, is going to result in a major voltage drop along the way.

Add control relays to power the windows from a short run of power from a terminal bus, and use the factory wiring to send the trigger signal to the relay, no more burned out contacts in switches, no more slow motors and given the low current going through the modified factory wiring, it will be trouble free for many more years to come.

1. I am experienced with, but in no way an expert in, W123 electrical.
2. I do not mean to be argumentative.

In response to the above...
>>To my way of thinking, the only pressing area for using relays is for the headlights. I say this based upon an understanding that a great deal of current passes through the headlight switch on the way to the lamps *and* that the occassional W123 driver posting here has discussed experiencing an under-dashboard fire due to all that current travelling in a historically humid environment (so they have written).

>>Within my two W123s, I've seen quite a bit of the wirig up close over the last 30 years or so and have found evidence of precious little corrosion (vehicles kept in both coastal and desert climates, always garaged).

>>If unexpectedly high resistance or significant voltage drops are suspected somewhere, I'd be inclined to simply use a VOM to measure and collect any evidence of said if it exists and take appropriate action if indicated.

87tdwagen · #15 12-24-2020, 12:02 AM

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