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Mack&Cheese

Tachometer doesn't go above 1400 RPM,

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Mack&Cheese    0

On my '91 Mack RD688S the tachometer doesn't move much at all and usually stays in the 1400 RPM range regardless of engine speed.

Where should I look first?

Thanks!

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Mack&Cheese    0

Thanks Jim, I will start there first.  Appreciate the feedback!

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Mack&Cheese    0

As it turns out the tachometer input is mechanical.  Changed out cable with new obtained from Mack and tachometer exhibits the same fault (when running the tachometer won't go below 5-600 rpm and no higher than 1400 rpm.  Very sluggish.  In my troubleshooting I also found that the incandescent light bulb that is suppose to be plugged into the back of the tachometer was not plugged in, so I suspect that the insides of the tachometer are full of dust and contributing to the sluggish operation, and apparent sticking of movement.  Anyone know how to take these apart??

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j hancock    8,491

The bezel is crimped on to the case.  Gauge shops have a tool to open the crimp, repair and then re-crimp the bezel.

If you take the gauge out, try some gentle compressed air to blow the dirt out.  It might work?  Tachs are not too expensive so if it doesn't clean up put a new one in.

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