I am in the process of getting my vette into semi-reliable running order and I have very limited time to work on it. I have intentions of finishing a fair amount of work over the last couple of cold months here in Nebraska while I can't drive it. The problem I am running into is the vehicle is stored at a place an hour away so when I do get a chance to work on it I want to be able to work and not sit on the computer or digging through manuals trying to figure out what's wrong. So this brings me to my question...

I have been trying to get the Speedometer and Tach working since I bought the car a few months ago but with the little time I have to work I never seem to get much done.... I have replaced the tach circuit board which had a large black spot on it thinking this had to be the problem. I also have checked both the upper and lower speedo cables in attempts to get the speedometer working. Neither the tach or speedo are working yet so I am hoping it is the Speedo/Tach printed circuit board that is keeping them from working. My question is how easy is it to get to this and can it be checked visually? I don't want to spend a bunch of time tracking it down to inspect it if it won't do me any good.

I also have a leak coming from between the master cylinder and brake booster so I was wondering how long it would take to change out the gasket between the two??? Any help would be much appreciated.

 

Don't know all that much about the Speedo or Tach. Sorry.

If you have brake fluid coming out from between the master cylinder and the vacumn booster, the gasket is probally not the problem. The rear seal/o-ring in the master cylinder is bad. This is where the acuator from the brake pedal engages the back of the master cylinder. If you remove the master cylinder, look at the back, if there is fluid where the rod engages then you have found the problem.

You can buy a complete rebuild kit for the master cylinder and rebuild it, but since you seem to have limited time, maybe getting a completly rebuilt master cylinder might be the way to go.

Grant

 

Aside from the bulbs that light the speedo, it is 100% mechanical. As far as your tach, since you have already replaced the tach circuit board, have you checked to make sure there is an electrical signal present at the large printed circuit board for the instrument cluster? The printed circuit boards go bad as well. It's just flat copper circuits laminated between two pieces of clear plastic. Mine de-laminated and the copper was pushed around and torn. IF you don't have a signal, start at the distributor and make sure the tach wire is plugged in. Trace it back to the instruments from there. I have the wire diagram for my '80. If you want I can tell you the wire colors to follow from start to finish.

If both your speedo cables are present and hooked up are you sure that the gear is in the transmission to spin the cable? Will the speedo needle rise if you turn the gears from behind? What about the junction point that connects the two cables?

 

Ak. Mal, I will be sure to check the gear in the transmission this weekend when I head back. As for spinning the cables to see if they work I was able to spin the upper cable and it moved the needle so I have eliminated any troubles within the actual gauge. As for the cruise control transducer I am unsure of how to check it? I also would very much so appreciate it if you could get me the info on checking the wiring.

 

From the distributor to the speedo/tach printed circuit board the distributor wire is the white one. At the gauges, the pink/black wire is the 12vdc power to the gauge cluster. *edit* The P/B wire is not power to the cluster, just the gauges themselves.

Send me your email address via pm. I have something that will help you with your electric work.

 

Doesn't the speedo cable run through the cruise control valve?
Only been a Vette owner for 6 months so I still know diddly..
But my speedo/tach don't work either and the cruise control valve is definitely bad.

 

If the speedo isn't working it may well be the gear in the tranny. I just replaced mine. It is a nylon gear and you can get them for about 9 bux.you need to know the number of teeth or color of the gear. Mine was stripped. My speedo was all over the dial. The needle would jump around.

 

You didn't say if you had lights in your speedo and tach............... make sure you've got a good ground ! I retrofitted an '80 wiring harness into a '76 and had a heck of a time.

I got everything connected up and had no speedo and tach lighting. After weeks of searching and pouring over the wiring diagram, I found out that GM (with their infinite wisdom !) ran the power for the speedo and tach lighting thru the windshield wiper switch ! I don't remember about the ground for this, but if you're having issues, you might check the power and ground !

You should also have a tach filter near the distributor.................. many guys have had problems with the tach not working because the filter was bad or missing....... check that too ! Rick