1977 Tach Filter question.
Thread Starter
Intermediate
Joined: Oct 2013
Posts: 49
Likes: 0
From: Loveland Colorado
1977 Tach Filter question.
I just purchased a 1977 C3 and when I first looked at it, the Tach was working fine. When I bought it the Tach no longer works. I looked through the forum and found out it should have a low pass filter in line with the tach signal coming out of the HEI. There is no filter in line with BROWN tach wire coming off the HEI and heading through the firewall. My question is that I assume the previous owner removed it for some reason and pluged the brown tach wire into the HEI. Would running without the filter take out the Tach circuit board over time?
Pro
Joined: Oct 2009
Posts: 523
Likes: 4
From: Calgary Alberta
I just purchased a 1977 C3 and when I first looked at it, the Tach was working fine. When I bought it the Tach no longer works. I looked through the forum and found out it should have a low pass filter in line with the tach signal coming out of the HEI. There is no filter in line with BROWN tach wire coming off the HEI and heading through the firewall. My question is that I assume the previous owner removed it for some reason and pluged the brown tach wire into the HEI. Would running without the filter take out the Tach circuit board over time?
If your tach stopped working then it might be the tach board itself as they have been known to fail over time.
Do a search or check with Willcox as they have some information on their site about testing and replacing the tach board.
Hope that helps!
Last edited by donyue; Oct 29, 2013 at 06:39 PM.
Instructor
Joined: Sep 2010
Posts: 236
Likes: 0
The tachometer in my '78 was fluctuating wildly. Over time I read in the Forum that it could be either the filter or the tach board. I decided to get a new filter. I figured this might be cheaper and easier to do than replacing the board. This solved my problem! Tach works fine now. If the problem had persisted, I would have moved to replacing the board.
