I recently changed the belts on my 1983 300TD. Afterwards, the tach went crazy and started intermittently pegging out, cutting off, etc.

I found the pickup sensor near the harmonic balancer on the crankshaft and disconnected it for examination (a real treat to get to). I noted that it had a nice groove cut into the plastic covering (I suspect from the detection pin on the crankshaft pulley). This exposed the metal underneath, but does not look overly damaged. I do not know if I might have inadvertently bent the sensor toward the pulley when replacing the belts or if this happened sometime in the past. I assume that this is the problem, but I also noted that pushing on the tach sending unit that I traced the pickup wire to, caused the same gyrations with the tach.

I want to reinstall the pickup to see if the problem goes away, but I don't know what kind of clearance to leave between the pin and the pickup in case I accidently bent the pickup holder bracket. I do not see any way to adjust this other than bending the bracket.

Any pointers would be appreciated. Again all was working fine until the belt change.

Thanks