Serpentine Belt
 

How do I adjust the tension on my belt on a 92 300E. When I start the car or sometime with the A/C on at a stop light or something the car wold make a ugly knocking noise and I found out that its the belt tensioner, but I dont know how to adjust it to be a little more tight. Anyone know how?

Based on your question, you must not have a shop manual. My advice is to simply stop at an independent shop specializing in MB or foreign cars and pay them to adjust it. I say this because, it is likely, based on my experiences with three different 300E's that when you attempt to adjust it the tensioner will prove to be bad and require replacement. Probable $400 overall.

If do decide to try it yourself, be aware that there is a large , 17MM at least, bolt that must be loosened prior to turning the adjusting nut. Failure to loosen this bolt can destroy the adjusting rod when you try to adjust against an immovable object.

Steve

thanx, any idea where the 17mm bolt is located?

Based on your symptoms, I don't believe adjusting the tensioner will solve your problem.

What generally goes bad on these things is the bushing that holds the tensioner shock to the assembly. When it gets worn, it gets noisy, usually at idle. Sounds like a rod is about to go when it gets really bad.

A far cheaper alternative to replacing the whole assembly. Do a seach on "tensioner bushing" to get more info...

yes your right, the bushing on it was bad and I did fix it about a month ago but the belt seems to be a little loose. I did find the screw and it's not 17mm it's 19mm. I loosened it and gave the tensioner screw a couple of turn and the belt did get tight and now the sound is gone. Thanx everyone......I do need to replace the belt though.....the belt seemes to be really streched.

There is an indicator and a pointer just below the adjuster nut. There is a spec as to where to adjust the pointer. You don't want the belt to be too tight. Do a search in this Forum on maybe Belt Tensioner Pointer and you should find the correct spec.

Steve