Tach Problems... Final Word
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 3,280
Likes: 0
From: Virginia Beach Virginia
Tach Problems... Final Word
My '75 Corvette's Tachometer quit working about 6 months ago. I read the archived threads and am uncertain how to troubleshoot because there seem to be conflicting opinions about whether the circuit board or tach filter is the usual culprit.
I prefer to not have to get in the dash and replace the circuit board, if it's not neccessary. But how can I test to see whether the circuit board is the problem or the filter?
I appreciate all your help!
Stephen
I prefer to not have to get in the dash and replace the circuit board, if it's not neccessary. But how can I test to see whether the circuit board is the problem or the filter?
I appreciate all your help!
Stephen
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Re: Tach Problems... Final Word (VolVette)
Just jumper out the tach filter, hook it up directly, and see if the thing works....
you will get some erronious indications, but if the tach is working the needle will move more or less normally.....
if so, replace the filter, if not, the tach is bad.....
if you need the filter....look/search here for a schematic and make one up....
GENE
you will get some erronious indications, but if the tach is working the needle will move more or less normally.....
if so, replace the filter, if not, the tach is bad.....
if you need the filter....look/search here for a schematic and make one up....
GENE
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 3,280
Likes: 0
From: Virginia Beach Virginia
Re: Tach Problems... Final Word (mrvette)
Thanks for the post!
There were some who posted saying that they bypassed the filter with no improvement, figured it was the circuit board and replaced it only to find that the filter was the problem. Can anyone else validate this?
Thanks,
Stephen
There were some who posted saying that they bypassed the filter with no improvement, figured it was the circuit board and replaced it only to find that the filter was the problem. Can anyone else validate this?
Thanks,
Stephen
Intermediate
Joined: Feb 2002
Posts: 34
Likes: 0
From: Odessa FL
Re: Tach Problems... Final Word (VolVette)
I have a problem with my tach also. It works but reads too high. I don't have a tach filter that I can find, so I am interested in any info on the subject too.
Pro
Joined: Aug 1999
Posts: 749
Likes: 0
From: Perth,Western Australia,Australia
Re: Tach Problems... Final Word (VolVette)
As mentioned you can bridge out the tach filter,if you are still having problems it's not the tach filter.By bridging the filter you are in effect having a wire run from the distributor direct to the tach.You may then need to replace the circuit board.
Neil.
Neil.
2nd Gear
Joined: Mar 2003
Posts: 2
Likes: 0
From: Lake Ronkonkoma NY
Re: Tach Problems... Final Word (Fleetwood)
Fellow C3'ers I too have wrestled with this. I have some insight:
If your tach is not working at all:
1. test connections using ohm meter and see if you get a slight change from the wire that is coming from distributor (usually brown). Make sure the connection is good no green/rust or deterioration. Mine was OK.
2. More than likely as in my case I had to replace the tach board. But that wasn't it. As I got the thing to work it was way off.
If your tach is working and bouncing around like crazy or it reads too high you may need to do one or all of the following:
1. Pull needle off and reset using engine analyzer to detect proper rpm and then place needle back on.
2. add noise suppressor (home-made) capacitor. You will need this if you experienced the same syptoms that I did which was erratic tach reading and at 2000 rpm's the tach went back down to 0. The tach sweep should be a smooth as your engine accelerates. If you need the details I will send..It is about 8$ worth of radio shack parts and if you have a soldering iron you're golden.
Hope this helps,
Willieo
If your tach is not working at all:
1. test connections using ohm meter and see if you get a slight change from the wire that is coming from distributor (usually brown). Make sure the connection is good no green/rust or deterioration. Mine was OK.
2. More than likely as in my case I had to replace the tach board. But that wasn't it. As I got the thing to work it was way off.
If your tach is working and bouncing around like crazy or it reads too high you may need to do one or all of the following:
1. Pull needle off and reset using engine analyzer to detect proper rpm and then place needle back on.
2. add noise suppressor (home-made) capacitor. You will need this if you experienced the same syptoms that I did which was erratic tach reading and at 2000 rpm's the tach went back down to 0. The tach sweep should be a smooth as your engine accelerates. If you need the details I will send..It is about 8$ worth of radio shack parts and if you have a soldering iron you're golden.
Hope this helps,
Willieo
