tach fix
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Senior Member
Joined: May 2008
Posts: 722
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From: SF bay area
Car: 86 Camaro iroc-z28
Engine: 305 TPI
Transmission: 700R4
Axle/Gears: 3.42 Posi
tach fix
i recently took out the stock tach in my 86 iroc with a 305 tpi, since it read wayyy too high, it would always hit maximum rpms whenever i touched the pedal. so i figured like you guys mentioned, that it was obviously off and needed to be fixed, so i went ahead and bought one from another member, it swapped in fine, but when i went to turn on the car, it still had the same problem. now i understand that this a common problem among our cars, but the strange part is that not only is it off, but its almost like its the same as the one i just took out. is there any possible way that whatever is feeding the information to the gauge might be bad? or is it more possible that both tachs are broken? ive gone ahead and replaced the resistor in one of them so i can swap the original tach back in
Supreme Member
Joined: Jan 2006
Posts: 3,341
Likes: 10
From: Mooresville NC
Car: LOWERED ♦ CRIMSON METALFLAKE
Engine: ► 400 KUBES ◄
Transmission: 765R4
Axle/Gears: EATON POSI 4.56
RPM MAYHEM
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You said you replaced the resistor.
Which one ?
The ‘information’ comes from tach lead off the dist.
It’s correct.
Your problem is in the circuit inside the dash that moves the pointer.
It’s contained on a small plug-in PCB.
On the PCB you’ll see a resistor chip.
Desolder pins 4 & 10.
Use a 500K potentiometer.
Solder it across traces 4 & 10.
Move the potentiometer to half way.
Start the engine and compare the tach reading with a test equipment quality tach.
Dial it in, unsolder one side of the potentiometer, measure it and buy the matching resistor.
.
Happy Racing!
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If People Drove Any Slower They’d Be Going Backwards.
.
.
You said you replaced the resistor.
Which one ?
The ‘information’ comes from tach lead off the dist.
It’s correct.
Your problem is in the circuit inside the dash that moves the pointer.
It’s contained on a small plug-in PCB.
On the PCB you’ll see a resistor chip.
Desolder pins 4 & 10.
Use a 500K potentiometer.
Solder it across traces 4 & 10.
Move the potentiometer to half way.
Start the engine and compare the tach reading with a test equipment quality tach.
Dial it in, unsolder one side of the potentiometer, measure it and buy the matching resistor.
.
Happy Racing!
.
If People Drove Any Slower They’d Be Going Backwards
.
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