Questions and Answers

Mercedes Benz 190 Belt Tensioner Q. I own a 1992 Mercedes Benz 190 with a 2.6 liter engine, automatic transmission and 180,000 miles. The serpentine belt became loose, so I bought a new one. I put the new belt on, loosened the large bolt on the belt tensioner and tried to tighten the belt by turning the small (13mm) nut next to the power steering pump.

As I tried to tighten the nut, it would tighten so far, and then slip, like the treads may be stripped. Will I have to replace the entire belt tensioner or just the adjustment bolt? If I have to replace the entire tensioner how do I go about it? Where is the best (best price) place to buy Mercedes parts?

A. It's very possible that just the nut is stripped. Normally manufacturers make the nuts out of softer metal than the bolts to prevent having to replace the bolt, which in this case I believe is a stud that is integral with the tensioner.

The only way to find out for sure is to remove the nut and inspect the threads and try a new nut on it. You can pick up a replacement nut at any parts store for a few cents. If the threads on the stud are in fact damaged you can probably have a reputable machine shop replace it for less money than replacing the entire tensioner assembly.