1983 300TD Tachometer Problem

[Benz_Dad]

I did not receive any responses to my earlier post, so here goes again.

I recently changed belts on my son's 1983 300TD. We are not positive (may be coincedental), but the tach went crazy after the repair (pegging out, cutting off, etc.).

I thought that I might have damaged the pickup sensor mounted near the crankshaft pulley, so I removed it for examination (a real fun job). I found that a groove had been cut in the tip of the sensor (less than 1/8 inch). I suspect by the crankshaft pin that the sensor is supposed to detect. I guess I could have bent the bracket even though it is nowhere near where I was working on the belts and is quite substantial.

I ordered a replacement pickup, but was sent a sensor module by mistake. I tried it anyway with the same results. I also tried the cigarette butt trick as well. I can find no consistent pattern caused by wiggling the sensor, sensor wiring, or sensor module.

Does anyone know how I can test the sensor pickup or sensor module (I guess I could have gotten a defective one)?

Also, what is the clearance supposed to be between the pickup and the crankshaft detector pin?

Any ideas or tests would be much appreciated.


Thanks

1983 300TD 2-owner 278k