Not sure if something broke or just came loose, but my tach stopped working and the needle sits pegged at 7k rpm. It still moves and it drops back to 0 when the engine is off.

Come to think of it, I haven't looked if it jumps up with power or only if the engine is running. I will check on that in the morning. Anyone have a quick fix or at least a place to start looking?


On another note, where is the best place to track down the gears for the speedometer cable? My new rims are different size than the factory ones, so I need to swap that out to get the speedo to read properly, but I can't find a place that carries them.

Thanks.

 

For the speedo, here is a link with a table for the correct gears depending on tire height and axle ratio: http://www.transmissioncenter.net/sp...n_______va.htm

For the tach, I don't know if you are using a HEI distributor, but if so, the signal wire plugs into there (the front right corner pin if you are looking at the top of the connector as I recall). You can test the output with a DMM using the positive lead on the connection and with the negative lead to ground. If you are not getting a signal (I can't recall if you set it for AC or DC, either way the voltage will increase with engine speed) there is a problem with your pickup, module, or internal connections. If the signal is good, you could have a faulty tach or a short to hot in the wire.

 

Camaro tachs are notorious for going bad. There's a guy here on the TGO that repairs them for like $50, it has to do with a resistor or transistor ... radio shack part , but have to take out and send It to him.

Do a couple of searches, I'll see if I can dig up his name, might be in my PM box still.

 

https://www.thirdgen.org/forums/elec...meter-fix.html

 

Going to pull out the board tomorrow and check on that 4-10 resistor. That sounds exactly like the problem I'm having.

 

My tach and oil pressure are both on the same board behind the gauges so it is a little different than the ones in that other thread, but as far as I can tell, that wasn't the problem. I'm getting good resistance between all of the pin sets, no open circuits.

It pegs as soon as the key is turned and it gets power.

 

I'm assuming that the one on the right is for the tach. If so, it checks out.

 

It is the white chip with black strips. I think you need to measure between pins 4 and 10.

 

Ah, I feel dumb. I was looking at the chip upside down. I tested the wrong pin sets. checking it the correct way I found;
R1 = 3.76k
R2 = 3.85k
R3 = 1.92k
R4 = x
R5 = 7.28k
R6 = 2.94k
R4 is definitely dead. I will try the resistor fix, but any idea why R5 is so high? It is double what most other people were reporting in the other thread.

 

Same reason R4 dies, the resistor network is weak. I would replace both and tune R4 with a POT for a little better accuracy.

 

Turns out I read the wrong pin for R5. I was reading both the R5 and R6 resisters in sequence, that was why it was so high. Everything looks good except for the dead circuit on R4. I will get out and see if I can get that resister tonight and hopefully that will take care of it. Thanks guys.