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MG MGB Technical - stickey tachometer

My electrical tach (80MGB LE) sticks in the 2000-3000 rpm range. When rpms much higher, it breaks free and reads correctly, but will again stick when I slow down.
I have the tach out of it's case, and the needle does the same when moved by hand. It is as though the movement is binding somewhere, but I can't see any such. Any suggestions?
Thanks,
Billco518 PS email has changed from wowway to att.net
Bill Cole

It is a very delicate mechanism so you are best sending it away for repair or replacing it, there is obviously something wrong with the pivot or more likely a spec of debris or damage between the moving coil and the fixed magnets.
Paul Hunt

Bill: I own a 1980 MGB/LE also. When I first start my car the tach stays at 0 rpm's for about 20 seconds then runs normally. If I tap the glass it takes off immediately. Being a "precision" instrument I'd do what Paul suggested. Good luck, Barry
B.R. Crum

Barry, the old tach (from a 78B) I use in my temporary dashboard does exactly that too. Start the car and it doesn't move but tap the glass and off it goes.

I have a brand new, after-market tach for the car when I starts finishing her off so it has never worried me too much.

Simon
Simon Jansen

Our 78 1800 Roadster does the same as Barry and Simon's - can't say it worries much - yet
Roger
Roger

Thanks to all that replied. Sounds like a somewhat common problem. Mine also responds to taping. Its now out of the case on the bench and I'm not willing to give up yet. A slight outward pressure on the inner dial face eliminates the problem, so something seems to have warped. The problem used to go away after things warmed up, but no longer, so the hunt goes on. Bill
Bill Cole

One of the problems is that the needle sticks to the little stop pin.. Apparently there is a covering on the pin that has gone sticky. Remove the glass and clean the little stop pin and then the needle will not stick.
Sandy
SANDY SANDERS

Sandy, I can try that on mine. As I am not using it in the car it doesn't matter so much if I mess it up! Will try it this weekend and let people know.

Simon
Simon Jansen

The tach now works! I don't like the solution, but here it is for the ambitious. When the needle would stick, I found very slight upward pressure on one side of the inside of the dial face would free the needle. Same with upward pressure on the top of the metal casting holding the meter together. Lacking a better solution (expert repair was quoted at $175 + shipping) I took the Rube Goldberg approach. I fashioned a small stick of wood, about 1/8" in diameter, and just long enough to wedge between the plastic meter frame and the underside of the dial. In my case, the pressure spot is just on the center side of the 0 on the dial. With my splint wedged in, the meter is free as a bird. I also checked operation cold (two hours in the fridge) and still worked perfectly. Did I mention that my problem was temperature sensitive, worse cold, better to non-existant when hot? Also rechecked hot to about 110 degrees in the residual heat of the kitchen oven.
Satisfied with the operation, I put a few drops of quick-cure epoxy around each end of the splint to secure it, and the the tach is back in its case and operating. Crude, but works and is free!
Bill
Bill Cole

Nothing crude about that Bill. I would call it elegant. After all, you even used epoxy.

Now take part of that $175 you just saved and go splurge on a bottle of your favorite expensive Bourbon.

Charley
C R Huff

I took mine apart to clean the sticky pin then discovered on the later dials there is no pin! Still, since it was open I had a look inside and couldn't see any reason for it sticking.
Simon Jansen

Yeah Bill! What Charley said but only after the "B" is parked!!! Glad you got it working. Barry
B.R. Crum

This thread was discussed between 26/08/2009 and 02/09/2009

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