tacho not working

[pauld]

I wondered if any of you guys have had this problem:-

I replaced the tacho circuit board and when i turn on the ignition, the needle goes back to zero. When the car is started the needle still registers zero and doesn't move. If i then drive the car and kick down or rev the car hard the needle then jumps up and then goes of the scale and stays there until i kick down or rev engine hard.

I bypassed the supressor on the lead from the distributor, but still no good.

HELP!!! any ideas???

 

[Jack]

Did you "zero the needle"?

Try this sequence first:
Run motor ... then switch off ... then switch on but do not start ... then switch off ... then gently pull needle off shaft & replace it to point at zero. Then run motor & check for correct operation.

If that sequence doesn't work for you, try this:
Run motor ... then switch off ... then switch on but do not start ... then gently pull needle off shaft & replace it to point at zero ... then switch off. Then run motor & check for correct operation.
JACK:gap

 

[pauld]

Thanks Jack, but you might be misunderstanding me, It is not that the tach needle isn't zeroing, it is that he only moves at all when reving motor hard and then sticks.

The needle goes to zero when ignition is switched on prior to starting but then stays at zero.

 

[Bob Chadwick]

My tach, and several other gauges, was giving me fits a while back. Turned out to be the 10 amp gauge fuse had blown.

 

[theo]

Hi Paul,
I was just browsing past this site, when i saw your post - I've just registered so i could put in a reply... How's that for motivation?!

Seems you have the same problem as me. I read a thread on the 77 vette forum about this. Some people are saying that the filter is essential, not just to get rid of radio interference, but to protect the circuit board from being fried. If this is true (i can honestly say i don't know either way) then i hate to say it but perhaps bypassing it has fried the new board. However, I was speaking to a guy at Corvette kingdom in Norfolk about this the other day, and he reckons they never see any problems just pulling the filter out completely, when it eventually corrodes up and dies.
So who do you believe? GM don't make the filter any more, but there is a guy in the US who i was told about, who makes his own. Have a look on the 77 vette site - http://www.1-4u-computer-graphics.com/cgi-bin/yabb/YaBB.cgi?board=perf;action=display;num=1053885090
and see what you make of it. I hope you haven't fried your board.... I think the fact its "parking" at zero suggests that the 12v and earth pins in the cluster are good, but perhaps that there is nothing coming to the pulse pin, ie from the dist. cap. This would make you think the filters died. I'm a bit bloody confused with all the conflicting arguments to be honest!
I want to get to the bottom of this one too, so lets see what we can find out!

 

[theo]

Sorry mate, seems that link isnt working - my fault. It works if you just cut and paste it though!