Tachometer troubles
Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
Tachometer troubles
Help!! The tach on my '76 L-48 doesn't work. I pulled it and found a burn mark on the circuit board. I replaced the board, along with a new filter. I adjusted the zero ok, but when I start the car, I get nothing, it stays on zero. With the tach disconnected, and the engine running, I get 12 volts from the pink wire, and 16 volts from the brown wire. I also noticed resistors R3 and R4 were hot after a few minutes of running. Is it maybe a distributor problem? Any help is appreciated.
Melting Slicks
Joined: Nov 2003
Posts: 2,668
Likes: 119
From: St. Charles Mo
CI 5 & 8 Veteran
Originally Posted by billsfan
Help!! The tach on my '76 L-48 doesn't work. I pulled it and found a burn mark on the circuit board. I replaced the board, along with a new filter. I adjusted the zero ok, but when I start the car, I get nothing, it stays on zero. With the tach disconnected, and the engine running, I get 12 volts from the pink wire, and 16 volts from the brown wire. I also noticed resistors R3 and R4 were hot after a few minutes of running. Is it maybe a distributor problem? Any help is appreciated.
Bullshark
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by billsfan
Help!! The tach on my '76 L-48 doesn't work. I pulled it and found a burn mark on the circuit board. I replaced the board, along with a new filter. I adjusted the zero ok, but when I start the car, I get nothing, it stays on zero. With the tach disconnected, and the engine running, I get 12 volts from the pink wire, and 16 volts from the brown wire. I also noticed resistors R3 and R4 were hot after a few minutes of running. Is it maybe a distributor problem? Any help is appreciated.
Assuming you did that, is there a chance that the needle is not moving freely? When you power on, can you see the needle actively move to zero?
At the tach filter, are both connectors good? You have one to the dash harness and one to the distributor.
Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
Originally Posted by Bullshark
Did you verify a pulse train signal at the tach output of the distributor? With the engine running. If you don't have a scope, you could use an external tach/dwell meter. Then verify at the input and output of your tach filter just for the hell of it.
Bullshark
Bullshark
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Thread Starter
Racer
Joined: Oct 2006
Posts: 396
Likes: 3
From: Buffalo New York
See my reply to Bullshark. When I pulled the old board off, there were no washers under it, thus my confusion. By the way, the instructions from Mid America didn't mention any washers. Except for that mishap, the fix was easy, including zeroing the tach. Now I've got to figure out how to put my dash back together. Thanks for the help!
Safety Car
Joined: Mar 2005
Posts: 4,255
Likes: 82
From: Brampton Ont.
Originally Posted by Jud Chapin
Can someone tell me where the tach filter is?
It's located on the drivers side, right in front of the distributor, with a wire coming out of the lower end of the cap. So look between the rear of the carb and infront of the distributor. If it's the stock filter then it's about 2 inches long and thicker than a cigarette. with one single wire coming out of each end. Hope this helps.
Race Director
Joined: Sep 2001
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From: Wellington, FL
St. Jude Donor '11 thru '25
Originally Posted by Maymyvetteliveforevr
It's located on the drivers side, right in front of the distributor, with a wire coming out of the lower end of the cap. So look between the rear of the carb and infront of the distributor. If it's the stock filter then it's about 2 inches long and thicker than a cigarette. with one single wire coming out of each end. Hope this helps.
Racer
Joined: Jul 2004
Posts: 471
Likes: 0
From: Raleigh NC
So guys, I'm looking at a '75 vert that I may buy - 1 owner car and he says the tach just started acting weird recently. It fluctuates and hangs at 2k, 3k when he turns the car off. Is the anything other than a dash biopsy that could fix the issue that anyone has found? That's a negotiating point for sure if the dash has to come out - did it 20yrs ago on a '76, still have nightmares.....