I replaced the tachometer on my 74 corvette, because the original tach was only working on occasion (typically at higher speeds). With the new tach in, I'm still having the same problem. Even when the car is at idle, nothing is registering. Does this mean there's a problem with the tach cable? Has anyone else had a problem like this? I'm really hoping I don't have to take the console off again...

 

It is most likely the cross gear in the dist. This is a very common problem. The dist does have to come out but the repair is fairly simple. Disconnect the cable at the dist. Have someone in the car and rotate thecable with your fingers. They should see the tach move. If so it is in the dist. If not maybe your cable is broken.

 

Due to some of the angle of the mechanical tach drive cable, it is possible that the cable is impinged on its inside movement. When I had a similar problem I found that the cable housing was bent and was preventing the cable from spinning within the cable housing. Due to the position of the distributor the cable connection may be at a bad angle. Disconnect the cable from the distributor and check that the inside cable is still intact. You can spin it by hand in both directions and see if there is any movement in your tach at all.

If there is, then inspect the internal cable for damage, and areas that may affect its free movement.

If the cable movement causes movement on your tachometer, then the problem is most likely with the tach drive gear inside of your distributor. This can be taken out by removing the large slotted screw at the input of the distributor housing, and removing the helical tach drive gear. Inspect this gear for worn teeth. If it is gound down, then you may have to pull the distributor to replace the main distributor drive shaft with the corresponding gear on it also.

see below for photo of damaged tach cable housing that was the source of my trouble.
kdf