Loose Serpentine Belt

[Andrew Freimuth]

I have a 1991 300te MB. Two months ago I installed a new belt. Recently it loosened and started slipping. It became so loose I could remove the belt. I have tried to adjust the belt tensioner but it will not adjust enough to tighten the belt. All the components seem solid...(no loose alternator, etc..) I am assuming I have a bad belt tensioner. Is this correct or should I look at something else before purchasing the tensioner???

[pifcat2]

It's a common mistake that people try to adjust the tensioner screw without loosening the lock bolt. You may want to replace the attached gas spring too.

[Gilly]

It's not uncommon for the tensioner to fail either.

Gilly

[sbourg]

Assuming you know (and knew) the proper way to adjust belt tension, then the tensioner is likely all that has failed. Tension is provided by torsion on a molded rubber bushing, and the bushing separates with deterioration from age. If you ever adjusted the tension without loosening the locking bolt, then you probably also broke the adjuster - ordered separately.

Steve

[PaulG]

Check that the tensioner actually tensinns the belt, it may have siezed.

If it's ok, just buy the next size belt down.