Tach issues
Thread Starter
8th Gear
Joined: Sep 2014
Posts: 8
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Tach issues
I have a 1979 corvette that has a tach problem. I have watched the willcox videos and tried to follow them to the letter. Set needle at zero with key on, started car ad needle goes up to 500 rpm. When I step on the throttle the needle goes backwards not forwards. Reset zero at 3000 rpm and same holds true goes up 500rpm then goes backwards with increase of throttle. It seems to be accurate in its negative travel. Any Ideas?
Instructor
Joined: Aug 2010
Posts: 129
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My first thought is that you may not have reset the pin that the needle attaches to. It should click if it needs to. I missed that and got erratic readings. I used a finishing nail push it down after I punched a hole in my fingernail. Sharp little sucker.
If you have clicked it in place, then start with the basics. Confirm that you have power and ground at the connector, 12V, key on. Check that you have continuity, ground connector to frame. Check that you have continuity + to - on the tach itself. You did not mention if you have a tach filter. Eliminate tach filter and plug directly into distributor, if you do. Is this a new board?
If you have clicked it in place, then start with the basics. Confirm that you have power and ground at the connector, 12V, key on. Check that you have continuity, ground connector to frame. Check that you have continuity + to - on the tach itself. You did not mention if you have a tach filter. Eliminate tach filter and plug directly into distributor, if you do. Is this a new board?
Thread Starter
8th Gear
Joined: Sep 2014
Posts: 8
Likes: 0
I have checked all of the things that you have mentioned so far. Voltage, ground, and polarity. There is no filter installed and the board is not new got it with car and has no markings to say it is anything but original. The needle functions its just backwards. Hate to buy a board and find something else is wrong.
Instructor
Joined: Aug 2010
Posts: 129
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Well, you have power, ground, and signal, and the board is evidently reading it wrong. Don't see that there is anything else to check. I suppose you could check the individual components populating the board, but that would require a schematic, and time. The failed board I replaced looked fine, no scorch marks or broken wires. Smelled fine too, not burnt. Maybe PM Willcox, but his response seems clear.
Former Vendor
Joined: Aug 2006
Posts: 76,656
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
If the needle goes backwards, only one side of the board is working.. yes, you need a board.
The board uses a single common a sign and co-sign. It pushes and pulls until a fixed RPM is obtained and then it flips. The pull becomes the push.
If you had purchased a new board, I'd tell you to loosen the nuts on the board and re-tighten them.. (bad contact). But since you are using a original board, I'd have to say the board has tanked.
Willcox
The board uses a single common a sign and co-sign. It pushes and pulls until a fixed RPM is obtained and then it flips. The pull becomes the push.
If you had purchased a new board, I'd tell you to loosen the nuts on the board and re-tighten them.. (bad contact). But since you are using a original board, I'd have to say the board has tanked.
Willcox
Thread Starter
8th Gear
Joined: Sep 2014
Posts: 8
Likes: 0
If the needle goes backwards, only one side of the board is working.. yes, you need a board.
The board uses a single common a sign and co-sign. It pushes and pulls until a fixed RPM is obtained and then it flips. The pull becomes the push.
If you had purchased a new board, I'd tell you to loosen the nuts on the board and re-tighten them.. (bad contact). But since you are using a original board, I'd have to say the board has tanked.
Willcox
The board uses a single common a sign and co-sign. It pushes and pulls until a fixed RPM is obtained and then it flips. The pull becomes the push.
If you had purchased a new board, I'd tell you to loosen the nuts on the board and re-tighten them.. (bad contact). But since you are using a original board, I'd have to say the board has tanked.
Willcox
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