Topic: Dead tach.
in Forum: C3 Electrical
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I have an isuue with the tach in my '75...it's dead. It had a new board installed by the previous owner about 2 years ago. Would the issue be the board again, a ground issue, a loss of power, a loss of signal from the distributor? I'm going to be pulling the dash apart in the next few weeks to install some new dash speakers and I would like some guidance on how to methodically check these things out. When I say dead, I mean the needle stays below zero when the car is running. I tried the trick of bypassing the tach filter and got nothing. Thanks for any help.
Greg.
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Build Date: May 7, 1975. 383 w/267 RWHP/310 RWTQ
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Greer, SC - USA
Joined: 3/13/2012
Posts: 264
Vette(s): 1978 Black with Viking mural painted under hood AM/FM/CB radio, T-top and a 2013 Cyber Gray Grand Sport Coupe, 2LT for my daily driver
Case,
Between your tach and mine, we might hit zero. With my car off, it is reading betwen 200 & 300 rpm's. so if we average them out, we might hit zero hehehe
Warning: The surgeon general has declared that it is NOT unhealthy to smoke your competition AND I just discovered that my corvette is a hybred. It burns gas and rubber!
Lifetime MemberTemple City, CA - USA
Joined: 10/3/2010
Posts: 365
Vette(s): 1969 Daytona Yellow. 350 / Automatic.
And then there is my '69 tach. When I start the engine, the tach jumps around a little and then stops on any number from 0 to 7000 and stays there until the next time I start the engine. Ah, the joys of a classic car!
|UPDATED|3/1/2013 9:50:11 AM (AZT)|/UPDATED|
|UPDATED|3/1/2013 9:50:11 AM (AZT)|/UPDATED|
Lifetime MemberModerator
Duncanville, TX - USA
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
It is most likely a problem with the circuit board, but before condemning it, check to make sure the tach wire is plugged into the distributor cap properly. A loose connection there can certainly kill the tach. A broken wire coming off of the coil could also be a possibility. You could remove the top coil cover and have a look-see to verify that.
Sometimes the connection for the board to the gauge panel can be loose/corroded, or otherwise faulty. You might try unplugging it, and plugging ti back it to see if it helps. If none of the above corrects the issue, then I'd have to go with the board taking a doo-doo.
Sometimes the connection for the board to the gauge panel can be loose/corroded, or otherwise faulty. You might try unplugging it, and plugging ti back it to see if it helps. If none of the above corrects the issue, then I'd have to go with the board taking a doo-doo.
Joel Adams
C3VR Lifetime Member #56 
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Lifetime MemberEquinunk, PA - USA
Joined: 10/31/2007
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Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.
Mr. James, Sounds like your problem is a broken cable. Try looking at the elbow on the distributor. That is a common place to find a frayed end. "IF" that is the problem, while replaceing the cable, get the brass re-fit drive so you can plug/ attach the cable streight insted of on a nasty bend.
Adams' Apple said: It is most likely a problem with the circuit board, but before condemning it, check to make sure the tach wire is plugged into the distributor cap properly. A loose connection there can certainly kill the tach. A broken wire coming off of the coil could also be a possibility. You could remove the top coil cover and have a look-see to verify that.
Sometimes the connection for the board to the gauge panel can be loose/corroded, or otherwise faulty. You might try unplugging it, and plugging ti back it to see if it helps. If none of the above corrects the issue, then I'd have to go with the board taking a doo-doo.
Sometimes the connection for the board to the gauge panel can be loose/corroded, or otherwise faulty. You might try unplugging it, and plugging ti back it to see if it helps. If none of the above corrects the issue, then I'd have to go with the board taking a doo-doo.
Joel, would a loss of signal from the tach make it read less than zero? What I'm wondering is if I still have 12V shouldn't the tach at least read zero if there is no signal or am I missing something? I'll have to get my meter in there and check for voltage of course but is there a way of checking for signal with a meter?
Build Date: May 7, 1975. 383 w/267 RWHP/310 RWTQ
Update: I replaced the tach board today and the tach is working again. I couldn't see any bun marks on the board but it must have been toast. Looked like one from offshore. I put a Wilcox board in this time. 
Build Date: May 7, 1975. 383 w/267 RWHP/310 RWTQ
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Dang 'lectronic stuff....
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Lifetime MemberTemple City, CA - USA
Joined: 10/3/2010
Posts: 365
Vette(s): 1969 Daytona Yellow. 350 / Automatic.
Mr. Shark. Frustrated with trying to fix my horns (there will be questions about that in the correct forum) yesterday, I had my step-son remove the tach cable from the distributor. He wiggled the wire inside it and it didn't seem to be broken. He had some trouble getting it back in until we used a good strong light to see into the connection.
Now it works again! Shouldn't say 'again' as its never worked since I've owned the car. Don't know what he did exactly.
Yippee, one problem fixed!
Now it works again! Shouldn't say 'again' as its never worked since I've owned the car. Don't know what he did exactly.
Yippee, one problem fixed!
in Forum: C3 Electrical
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