Need Tach Diagnostic Help..., Tach freezes after car warms up.... Options

[nine14cats]

Need some diagnostic help here with my tachometer.

I have a 1976 2.0. All stock except a pertronix upgrade. Immediately after a cold start the tach registers fine. A few minutes later (and especially after driving on the street for 10 or more minutes), the tach will freeze, usually around 2K RPM.

Any ideas as to why? And how to fix?

Thanks in advance for the help!

Bill P.

P.S. The car has been sitting for the better part of a year.

[914GT]

That's odd. If it was the coil warming up and slightly changing the characteristics of the ignition pulses I'd expect the needle to bounce around or go to zero. Since it's stopping at 2000 that would seem to be more of a problem with the tach itself. Like it's warming up and expanding and binding the needle on the bezel at that particular spot. So after you shut the car off for awhile does the needle drop back to zero?

[nine14cats]

Hello Guy,

Yep...when I park the car the tach is stuck at 2K. The car cools down, the tach needle drops to 0K, and when I start her up cold...the tach reads like normal. A few minutes later the tach get stuck. As the car heats up...the tach starts stopping at 4K...then 3K...then finally sticks at 2K....

Pretty weird....have you heard of that one before?

Bill P.

[John]

I had one do that once.

In my case it was a problem with the tach. Actually the tach lens was bowed inward allowing the center to contact the lens. It seems like it started out in the morning working, and would then get stuck later. Sometimes you could tap on the tack and the needle would return to function for a while.

I replaced the plastic lens with a glass lens and haven't had a problem with it since.

Just something to look at.

[nine14cats]

bump...

I'll check the glass tomorrow during the day....

Bill P.

[bperry]

I had the same problem with my lense. The original lense in my 74 was
plastic not glass.
The way to tell if you have an issue is to look at your reflection
in the lense. If you see your face distorted and larger than normal,
then your lense is bowing convex towards the needle.

I went to an art supply house and cut a nice new clean piece of glass.
Be warned if you do replace it, be very careful not to shake the
gauge too much as you pry off the bezel.
If you do ( like I must have) you can chip off the paint on the needle.
Then, if you paint the needle, make sure that you put a tiny bit of oil
or grease on the stop. If you don't, the paint may stick to the post
in the summer when the temperature gets warmer and youll have to
open up the tach again.....

I'd also recommend using a tiny bit of silicone cement to tack the lense
in place, since in my case the new lense doesn't quite fit the same as
the old lense with the original gaskets. The cement will keep the lense
from moving or rattling.

Switching to glass was a real pain but the final result is nice
since there won't be any scratches or fogging.
Haven't had a problem with mine since I did this 15 years ago.

--- bill

[John]

Bill, where did you get a pic of my car for your avitar? (just kidding) It does look like my 83 turbo.

[Hydra]

i'm having the same problem with my tach but i also have a scratcn on the lense, the problem is i never new how to remove that lens, any hint anyone....?

[Dave_Darling]

Check this Tech Article from the Bird site:
http://www.pelicanparts.com/techarticles/M...auge_repair.htm

--DD

[nine14cats]

Thanks Dave!

Bill P.