The original slides are made of a very thin pastic and are very brittle. It is not uncommon to see this type break just due to age.
Problem & Solution
Common among these chassis:
Here is a recent technical question we received from a customer:
Year: 1991
Model: 560 SEL
Product Description: Door window slides
I replaced both rear door window slides a few months back and , guess what?,
one of them broke already. What could have caused that to happen.
The original slides are made of a very thin pastic and are very brittle. It is not uncommon to see this type break just due to age. But if you have one of the heavy duty solid slides that we sell and they are breaking then there may be a reason not related to the slide. These are made with some tough plastic and do not just break.
The only way they break is if they have been subjected to excessive stress. That can come at installation from hammering too hard on the rivet without support. Failure can also occur if there is binding in the window groves and / or the lifting mechanism (regulator).
Be sure to test the window up and down by hand before connecting to a regulator. If it does not run smoothly you need to fix the cause first. Make sure the regulator is not bent and that it moves smoothly. Lubricate the window glass channels with silicone spray and generously lubricate the slide and all metal moving parts with synthetic grease.