TACH Problems
Thread Starter
Racer
Joined: Apr 2006
Posts: 373
Likes: 0
From: Chipley Florida
TACH Problems
Hi i have a 1980 Corvette L-82.
The tach stop working last night on the way home from work. With the ignition off it stays at the 3500 rpm mark. When driving it stays at the 4000 rpm mark. Any ideas where to look first? should I replace the cable? it never drops back to zero nor is the any movement from the needle.
The tach stop working last night on the way home from work. With the ignition off it stays at the 3500 rpm mark. When driving it stays at the 4000 rpm mark. Any ideas where to look first? should I replace the cable? it never drops back to zero nor is the any movement from the needle.
Burning Brakes
Joined: May 2006
Posts: 774
Likes: 1
From: Round Rock Texas
Probably need it re-worked. I know most use a circuit board that always fails. Not sure about yours, but I would bet that is what has happened. Look at one of the Corvette parts sites and see if they have tach re-build service for your year model.
Melting Slicks
Joined: Apr 2008
Posts: 2,625
Likes: 242
From: Russell Ontario
St. Jude Donor '09
On mine the wire that goes to a noise supressor on the intake broke , I took the supressor out and wired them together and the tack started to work , cream coloured wire and a small bracket on the passenger side beside the distributor! or like above the tach printed circuit! Ron
Thread Starter
Racer
Joined: Apr 2006
Posts: 373
Likes: 0
From: Chipley Florida
Tach
I was just waiting to install it all, it looks like my weekend project for this weekend. thanks for the help!!!
Thread Starter
Racer
Joined: Apr 2006
Posts: 373
Likes: 0
From: Chipley Florida
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The areas of possible cause are: 1) bad signal wiring from tach to circuit board (behind gauge cluster); 2) bad tach signal filter (the little can mounted to the intake manifold in that tach signal line; 3) bad circuit board [see #1]; bad tachometer. The likelihood of those causes can be prioritized as #3, #1, #4, & #2 [IMO] because of the symptoms you described. But, since the circuit board and tach are the most difficult to check out/repair/replace, verify integrity of #1 & #2 first. If you pull the circuit board out, check it over very closely; the problem may simply be a broken conductor foil on the board which prevents the tach signal from getting to the tach. If so, a simple solder job can fix it and save a bunch of $$$$.
Thread Starter
Racer
Joined: Apr 2006
Posts: 373
Likes: 0
From: Chipley Florida
Tach
The areas of possible cause are: 1) bad signal wiring from tach to circuit board (behind gauge cluster); 2) bad tach signal filter (the little can mounted to the intake manifold in that tach signal line; 3) bad circuit board [see #1]; bad tachometer. The likelihood of those causes can be prioritized as #3, #1, #4, & #2 [IMO] because of the symptoms you described. But, since the circuit board and tach are the most difficult to check out/repair/replace, verify integrity of #1 & #2 first. If you pull the circuit board out, check it over very closely; the problem may simply be a broken conductor foil on the board which prevents the tach signal from getting to the tach. If so, a simple solder job can fix it and save a bunch of $$$$.
It stays at 3500 rpm when I am driving it or not (shut down) and will go to 4000 rpm and stay there and then drop no lower than 3500 rpm at slower speeds usually less than 45 mph.
I have replaced the circuit board for the center bezel with gauges and all the light bulbs as well as the lens. So I was planning on removing the tach and speed o and replace the lens there too along with the bulbs and circuit board I already bought. that way the dash will be completely re done with everything new.......thanks again!
Le Mans Master
Joined: Sep 2002
Posts: 5,236
Likes: 898
From: Myrtle Beach SC
Tach Repair
Thread Starter
Racer
Joined: Apr 2006
Posts: 373
Likes: 0
From: Chipley Florida
Tach repaired
Most often its the tach board...read this recently published article on tach boards in CE...
Tach Repair
Tach Repair
It works too!!!!
