Topic: Is there an easy way to test a tach?
in Forum: C3 Interior
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The tach in my 75 does not work. Someone had added a tach above the steering column, but it quit the other day. Is there an easy way to test the original tach to see if it actually works or not? It appears to still be wired.
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The electric tach on these early (post mech tach) cars are notorious for failing. When I got my 76, it was working, but read wrong at every point on the scale. One of the first things I did was pull out the driver's instrument panel (as you are doing now) and get the tach repair kit (common item at most of the vendors and consist of a new electrical board).
Also had to get the kit for the clock and send out the speedo head for new odometer gears. Over the years I have replaced the gas gauge, T gauge, ammeter (repaired that one twice and finally gave up and replaced it). Only the oil pressure gauge is still original, but everything works now. If you own a corvette, you kind of get used to getting back there....
BTW - I have dropped the steering column once during my body off exercise, but I have always been able to get the instrument panel out otherwise by just loosening the two large retaining bolts holding the column up as someone else suggested.
If you do drop and remove the column, you should replace the rag joint and get the assembly manual. There is a procedure in there to follow to get it all back together and realigned (critical to avoid having problems with the rag joint and possibly your column in the future.
Eventually, I will have to get the column rebuilt, but have put that off.... Somebody on this forum said these cars were not built to last. That is definitely true, but it is fun keeping them rebuilt....

tom43xy said: The electric tach on these early (post mech tach) cars are notorious for failing. When I got my 76, it was working, but read wrong at every point on the scale. One of the first things I did was pull out the driver's instrument panel (as you are doing now) and get the tach repair kit (common item at most of the vendors and consist of a new electrical board).
Also had to get the kit for the clock and send out the speedo head for new odometer gears. Over the years I have replaced the gas gauge, T gauge, ammeter (repaired that one twice and finally gave up and replaced it). Only the oil pressure gauge is still original, but everything works now. If you own a corvette, you kind of get used to getting back there....
BTW - I have dropped the steering column once during my body off exercise, but I have always been able to get the instrument panel out otherwise by just loosening the two large retaining bolts holding the column up as someone else suggested.
If you do drop and remove the column, you should replace the rag joint and get the assembly manual. There is a procedure in there to follow to get it all back together and realigned (critical to avoid having problems with the rag joint and possibly your column in the future.
Eventually, I will have to get the column rebuilt, but have put that off.... Somebody on this forum said these cars were not built to last. That is definitely true, but it is fun keeping them rebuilt....

Who did you have your odometer repaired by? The one quote I got was for over $300.00.
My temp and oil gauges had been bypassed with other ones installed under the dash, but the original ones worked fine when I hooked them up again -- no idea why they were replaced.
I fixed the clock myself by cleaning the points and lubing it, but it only ran for a day. I'll have to look at it again, but pulling the cluster is such a pain. . .
Thanks for the information!
I had my Speedo head rebuilt by a corvette specialty shop locally in Denver (Corvettes Only). I am sure they sent it out, but don't know to who. It was not cheap either and the reason I did it was that I could not source a replacement odometer gear. It was replaced with a steel gear, so I was happy with the result (almost 10 years ago now).
I think I saw a previous post recently for a source for these gears, so maybe that could work for you. I can get you a phone number for the shop in Denver if you need it, but you hopefully can find something local or closer for you.
tom43xy said: I had my Speedo head rebuilt by a corvette specialty shop locally in Denver (Corvettes Only). I am sure they sent it out, but don't know to who. It was not cheap either and the reason I did it was that I could not source a replacement odometer gear. It was replaced with a steel gear, so I was happy with the result (almost 10 years ago now).
I think I saw a previous post recently for a source for these gears, so maybe that could work for you. I can get you a phone number for the shop in Denver if you need it, but you hopefully can find something local or closer for you.
I just ordered new seat covers, so I added the odometer gear and tach circuit board to the order. When I have the seats pulled I'll pull the dash and see if I can fix them. I'll also take the clock apart again and see if I can get it working for more than a day.
Thanks again for the help.

SHELBYVILLE, TN - USA
Joined: 7/5/2002
Posts: 3942
Vette(s): 1976 L48 auto
1978 L82 4speed
1994 LT1 6speed
1978 L82 4speed
1994 LT1 6speed
dont forget about the tach filter.... if its "blown" your tach will not operate, or operate radically
just for quick reference... no offense to our sponsors
http://www.ecklerscorvette.com/corvette-tachometer-filter-original-barrel-style-1975-1989.html
stingrayjim jr said:
dont forget about the tach filter.... if its "blown" your tach will not operate, or operate radically
just for quick reference... no offense to our sponsors
http://www.ecklerscorvette.com/corvette-tachometer-filter-original-barrel-style-1975-1989.html
Thanks, I ordered the filter from Ecklers and it arrived today. I'll pull the dash after I finish recovering the seats, while they are still out of the car. I also got the new circuit board for the tach. I'll also take another stab at getting the clock running again. If all goes well, I may have all of the original gauges working again!
I got the seats almost recovered today. Strangely, on the backrest the new covers miss covering the bottom sides by almost 2 inches. I cut the bottom corners from the old seats and put that piece in place to cover the foam that was showing. I wonder if anyone else has had that issue? The covers came from Corvette America.
I also had a problem of some of the short clips breaking while trying to pull them through the foam back panel.
Covering the seats myself has been a challenge, but they did come out okay.
BillHanna said:
Thanks, I ordered the filter from Ecklers and it arrived today. I'll pull the dash after I finish recovering the seats, while they are still out of the car. I also got the new circuit board for the tach. I'll also take another stab at getting the clock running again. If all goes well, I may have all of the original gauges working again!
stingrayjim jr said:
dont forget about the tach filter.... if its "blown" your tach will not operate, or operate radically
just for quick reference... no offense to our sponsors
http://www.ecklerscorvette.com/corvette-tachometer-filter-original-barrel-style-1975-1989.html
Thanks, I ordered the filter from Ecklers and it arrived today. I'll pull the dash after I finish recovering the seats, while they are still out of the car. I also got the new circuit board for the tach. I'll also take another stab at getting the clock running again. If all goes well, I may have all of the original gauges working again!
I got the seats almost recovered today. Strangely, on the backrest the new covers miss covering the bottom sides by almost 2 inches. I cut the bottom corners from the old seats and put that piece in place to cover the foam that was showing. I wonder if anyone else has had that issue? The covers came from Corvette America.
I also had a problem of some of the short clips breaking while trying to pull them through the foam back panel.
Covering the seats myself has been a challenge, but they did come out okay.
Here's a quick update. I replaced the odometer gear and it now works. The reset function also works -- evidently many of these don't work.
I replaced the circuit board on the tach and also the condenser at the distributor, but now the tach reads way too high. I thought I saw where someone showed how to calibrate these -- does anyone have a link to that?
The seat recovering came out looking good, except for it not covering all the way down the sides. I'm thinking that these are not the original seats. Inside the leather it was stamped "1978" which was a few years after my car was built, and one of the rear bolts does not align with the holes in the floor. Does anyone know if later seats had a higher backrest?
When it was all done and I tried to start the car -- nothing! I finally traced it down to the connector on top of the steering column.
Thanks for everyone's help with this project. You all made it much easier for me.
Bill
Well, I found out that calibrating the tach to zero is simple -- but it needs to be out of the car to do it. You simply apply 12 volts to it, pull the needle off and push it back on at the zero position.
Problem is that I had installed the dash before I knew this -- I wish Corvette America had included that in their instructions.
So today I got brave and pulled the dash again, calibrated the tach to zero, and almost got everything back in place. I say almost, because it seems like the dash grew an inch while it was out! It is just too wide now! I took a break before I broke something, but at some point I need to figure out why it doesn't fit. Anyone else had this issue?
When this is back in place, I believe everything on this 75 will be working! When I got it, the only gauges that worked was the speedometer and gas gauge.
I like to do most of the work myself, but I just had my mechanic replace the emergency brake shoes. He had no end of problems, mostly because the stainless hardware kit I got had parts that did not fit, or were not made right. He used parts from two other (non-Corvette) hardware kits to make everything work. I'm glad he did not charge extra for the frustration aspect!
Problem is that I had installed the dash before I knew this -- I wish Corvette America had included that in their instructions.
So today I got brave and pulled the dash again, calibrated the tach to zero, and almost got everything back in place. I say almost, because it seems like the dash grew an inch while it was out! It is just too wide now! I took a break before I broke something, but at some point I need to figure out why it doesn't fit. Anyone else had this issue?
When this is back in place, I believe everything on this 75 will be working! When I got it, the only gauges that worked was the speedometer and gas gauge.
I like to do most of the work myself, but I just had my mechanic replace the emergency brake shoes. He had no end of problems, mostly because the stainless hardware kit I got had parts that did not fit, or were not made right. He used parts from two other (non-Corvette) hardware kits to make everything work. I'm glad he did not charge extra for the frustration aspect!
Update:
I got the dash back together -- the first time I had a problem getting the left side in place, and this time the left side went right in, so I put a screw in it. Well, I found that I needed to remove that screw so the dash could go to the left a bit, then the right side went in.
Now every gauge works, even the trip odometer, but when I turned the key to start, nothing! This happened last time I put the dash back in place. I thought it was the ignition switch on top of the steering column, so I had pulled the column, adjusted the switch, and it then started.
But this time I could hear the switch click, so rather than going through that again, I ran a wire direct to the starter from a button under the dash. It now starts and everything seems fine.
Maybe someday I'll get curious and brave and pull the steering column again to see what is going on with the switch, but it runs so I'll let it rest for now.
I have learned so much through the guys on this forum and I very much appreciate all the help I have gotten here!
I got the dash back together -- the first time I had a problem getting the left side in place, and this time the left side went right in, so I put a screw in it. Well, I found that I needed to remove that screw so the dash could go to the left a bit, then the right side went in.
Now every gauge works, even the trip odometer, but when I turned the key to start, nothing! This happened last time I put the dash back in place. I thought it was the ignition switch on top of the steering column, so I had pulled the column, adjusted the switch, and it then started.
But this time I could hear the switch click, so rather than going through that again, I ran a wire direct to the starter from a button under the dash. It now starts and everything seems fine.
Maybe someday I'll get curious and brave and pull the steering column again to see what is going on with the switch, but it runs so I'll let it rest for now.
I have learned so much through the guys on this forum and I very much appreciate all the help I have gotten here!
in Forum: C3 Interior
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