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Serpentine Belt Proper Tension on 190D 2.5

How do I know if my belt is a little loose? My tach and a/c die intermittantly and I’m thinking the belt might be slipping. It seems old and it flaps a at the top at idle but not when reved higher. Can this be adjusted by moving the alternator?

Push on the belt between two pulleys. If you get more than an inch or two deflection, it is too loose. Just get a new one and replace the old one.

belt tensioner and shock were common wear items on the 190’s. the a/c clutch was equipped with a “slippage” device that would turn off the compressor if belt slippage was detected. Chances are that you need a tensioner. The belt shock made a chattering sound at idle when replacement was needed because the bushing end wore out where it bolted to the engine. Great car though. The 2.5 was a really gutsy little diesel that was a lot of fun to drive, especially with the 5 speed.

Funny timing of this notification. Just this past week I had my belt, tensioner and shock changed on my 1988 2.6 190 E with 96,000 original miles, because my car was behaving the way you describe, but I think my belt was a little further gone. Mine got to the point where it would squeal like a heard of stuck pigs for about the first five humiliating miles, then quiet down.
I was told by the first mechanic (small shop) I took it to that the job required two specific tools, which he didn’t have because they cost about $600.
Being in a smaller city with few options, he recommended I take it to the dealer.
3.8 labor hours, and a little over $400 for the parts. Out the door was about $950.
So I’m hoping to not have to worry about it for another 96,000 miles.
Good luck!