Loose Alternator Belt on 1970's Models

Mercedes used a unique and clever way to adjust alternator belt tension during most of the mid to late 1970's. This covers 123 240D, 300D, 300CD 1977 to 1979. The head of the outboard mounting bolt actually has teeth machined into it. When you turn the head of the bolt either direction it will move the alternator in or out to loosen or tighten the v-belt tension.

This works great as long as the adjustment procedure is done properly and apparently more often than not it is done incorrectly. You must loosen ALL three bolts holding the alternator to the engine BEFORE turning this adjusting heat. If not you will strip off the teeth as you can see in this picture. Once these teeth strip you will have a very hard time getting your alternator belt tight enough.

Symptoms will be a squealing belt especially when the engine is cold. When you try to tighten your belt you may find it just won't adjust. Look closely at the teeth on the head of the adjusting bolt. If striped or rounded off order our new bolt replacement.

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