My 1974 240D eats alternator belts. The car is driven only a couple of hundred miles a month and I have had to replace 3 alternator belts with not more than about 2000 miles on them. I can't do the work myself any more and have been paying 1 hour labor ($87) plus the cost of the belt and a tow job to the shop. I have been telling the mechanic something is wrong but he says all is OK. When I look at the belt I see two things. 1. A straight edge on the alternator and crankshaft pulleys shows a little bit of misalignment. 2. The belt is riding deep in the alternator pulley. The belt looks like it is riding all the way on the bottom of the pulley. The broken belts appear to be worn through in one spot. I need some ideas.

 

I think you have given me the answer to my problem. The alternator is not original. My engine has a 10x970 belt. Since you said there is a 13mm belt used on some models, I think when the alternator was changed the pulley for a 13mm belt must have been what was on the new alternator. As I said the belt is riding at the bottom of the pulley. The pulley is obviously too wide for the belt. Do I need the engine number or will the VIN number do to get the right pulley? If I need the engine number, where is it.