Rear window sticks on way down. Motor or guides?

[Ceeker]

It's a 1991 318i M40B18 sedan.

Your motor is tired. replace the window motor. I have rebuilt a quite a few of these in the past. if it brings the window down easy and struggles going up. its the motor. You can use the other side but you will need to build them back up. the part circled in red are the brushes. You may see some flat spots of wear on it. this is where it hangs up while spinning to get the window to wind back up. the resistance wears them down; since less material is present makes for more resistance on the magnet; if it misses while spinning the motor stops all together and sometimes you have to bang the door panel to get it going again. I had problems with all 4 doors on my IX one time. the reason it isn't coming out because it is seized with corrosion. I also encountered the same thing as you.

[evilnickwong]

It's a 1991 318i M40B18 sedan.

[!kid]

what car is this for?

[evilnickwong]

It goes all the way up from bottom just fine.

From the top it goes down for only abit, then I have to help it by pushing the window down.

By the way, something else I did notice. Here is a photo of my left side rear motor + regulator (which DOES work) when I disassembled it for cleaning.



One thing I noticed when I was doing the same for the right side which doesn't work, is that the part circled in red, I couldn't remove it from the motor housing (blue part). On this left side that's pictured, it came out real easy, but on the side that doesn't work, it won't come out at all. I tugged at it all I could, but it wouldn't budge. Dunno if this means anything.

[bmwm42]

If the pulley are damaged teeth missing etc the motor can only roll the window down so far

[evilnickwong]

This brings up an interesting point. My car is a 1991 sedan.
Are the motors interchangeable from left to right? I would imagine they're not, but I dunno. I think from front to back definitely won't work since the front one is a sealed unit (at least for the innards, I know the commutator section can be removed) as compared to the rear one which can be completely taken apart.

Also, I understand that motors can obviously get weak with age.
But how are regulators the possible fault? They seem like just a simple cable/pulley system and if nothing is broken and it all moves properly, I don't see how it can be contributing to a stuck window.

Thanks for the input guys. :)

[!kid]

okay. what about taking the motor from another window and installing it on the bad side to rule out if its the motor or regulator.

[evilnickwong]

spray a good amount of WD40 on the cable thing if the issue goes away I would suggest taking the hole regulator out and giving it a good cleaning and re grease it.

I've done this already, cleaned all the old thick grease off and layed new grease on.

[!kid]

spray a good amount of WD40 on the cable thing if the issue goes away I would suggest taking the hole regulator out and giving it a good cleaning and re grease it.

[evilnickwong]

Regulator = the whole bit with the cable running along the 2 wheels at the top and bottom of the frame?

What about it can I try to fix?

[bmwm42]

The regulator

[evilnickwong]

My rear power window on one side hasn't been working for some time. I took it apart the other day to disassemble to motor and found the center shaft was rather corroded and rough. After smoothing it down and cleaning and lubing the rest of the bits in the motor, the regulator runs alright up and down on its own. (Just testing it connected to power on it's own)

But once I put it in and connect it up to the glass, it sticks on the way down. If I push down on the window to help it along, it struggles down. Oddly, going up which I thought would be harder works fine.

Is this just a weak motor, or are the rubber guides which are quite old creating too much resistance?