1970 Speedometer Repair

[James H.]

I have a 1970, LT1, and the speedometer and odometer is not working. No movement at all of either while driving. I have seen pictures of the mess it is when someone drops the dash and I am wondering if there is a way to troubleshoot this problem, looking for some more simple possible fixes that I should start with first, short of removing the entire gauge.

I have no idea if the problem is the gauge itself, or cable, etc. Any advice and idea would be appreciated.

Thanks

Jim

[Rex M.]

Re: 1970 Speedometer Repair

I had problems with my 70 Speedometer also. The first time it turned out to be the geardrive in the bottom of distributor. I hired a old Corvette mechanic to do that job and he knew exactly what to do. Then about two yrs later the mph needle quit working but the odometer still worked. I hired another mechanic to tear the dash apart, remove the speedometer and I sent it to Roger's Clock down in Tenn. He repaired it. Turned out the mechanic wasn't too good though. He broke the center gauge cluster, that costs me about $300. He also broke the second hand off the clock. I removed the dash to repair all those problems. It's a major job.

[James H.]

Re: 1970 Speedometer Repair

Isn't the cable coming from the distributor the cable that runs the tachometer?

It is possible I have a broken cable and maybe the speedometer is not the problem? I am hoping to troubleshoot it so i know the problem is the speedometer for sue before I try to remove it.

Thanks

Jim

I had problems with my 70 Speedometer also. The first time it turned out to be the geardrive in the bottom of distributor. I hired a old Corvette mechanic to do that job and he knew exactly what to do. Then about two yrs later the mph needle quit working but the odometer still worked. I hired another mechanic to tear the dash apart, remove the speedometer and I sent it to Roger's Clock down in Tenn. He repaired it. Turned out the mechanic wasn't too good though. He broke the center gauge cluster, that costs me about $300. He also broke the second hand off the clock. I removed the dash to repair all those problems. It's a major job.

[Joe L.]

Re: 1970 Speedometer Repair

Isn't the cable coming from the distributor the cable that runs the tachometer?

It is possible I have a broken cable and maybe the speedometer is not the problem? I am hoping to troubleshoot it so i know the problem is the speedometer for sue before I try to remove it.

Thanks

Jim

Jim------


Whether it's the instrument or the cable, you're going to have to get behind the dash. You might be able to remove the cable from the speedometer, though, without actually removing the dash. 1969 and later use a "snap on" type of cable retainer at the speedometer. If the cable turns when the car is in motion, then you know the problem is with the instrument. If the cable does not turn, then you know that the problem is with the cable OR the speedometer gears in the transmission. If it's with the cable, the cable has to be removed from the sheath at the speedometer end and cannot be removed at the transmission end.

[James H.]

Re: 1970 Speedometer Repair

Joe,

Do you know of any resources, manuals, YouTube, etc. that can guide me though removing and replacing the speedometer?

Thanks

Jim

Jim------


Whether it's the instrument or the cable, you're going to have to get behind the dash. You might be able to remove the cable from the speedometer, though, without actually removing the dash. 1969 and later use a "snap on" type of cable retainer at the speedometer. If the cable turns when the car is in motion, then you know the problem is with the instrument. If the cable does not turn, then you know that the problem is with the cable OR the speedometer gears in the transmission. If it's with the cable, the cable has to be removed from the sheath at the speedometer end and cannot be removed at the transmission end.

[Joe L.]

Re: 1970 Speedometer Repair

Joe,

Do you know of any resources, manuals, YouTube, etc. that can guide me though removing and replacing the speedometer?

Thanks

Jim

Jim-------


The best that I can offer is the 1970 Chevrolet Service Manual. This is a must-have reference for anyone that works on their 1970 Corvette. Of course, there may be videos on youtube but that I do not know.

[Mark E.]

Re: 1970 Speedometer Repair

Isn't the cable coming from the distributor the cable that runs the tachometer?

It is possible I have a broken cable and maybe the speedometer is not the problem? I am hoping to troubleshoot it so i know the problem is the speedometer for sue before I try to remove it.

Thanks

Jim

Yes, the tach is driven by a cable from the distributor. But this is completely separate from your speedo problem.

[Bill B.]

Re: 1970 Speedometer Repair

Either the cable is broken or the second and/or third worm gears in the gauge head are bad. Replacing the worms gears is very easy if you understand how things come apart, you are methodical taking apart, and handle things carefully. Can you repair a leaking shower head? If you can, then you can most likely repair your speedometer.

[James G.]

Re: 1970 Speedometer Repair

with an LT1 depending on your trans and rear ratio you may have a SW gear reducer on the side of the trans, this could also be bad, they have input gears and output gears and just screw onto the trans cable on the other side of the reducer. - there are also right angle reducers -

[Edward J.]

Re: 1970 Speedometer Repair

Jim you can unhook the cable at transmission and spin with you fingers and have someone watch the needle for movement. If it works then you problem maybe the driven gear on transmission.

[Bill B.]

Re: 1970 Speedometer Repair

I have a 1970, LT1, and the speedometer and odometer is not working. No movement at all of either while driving. I have seen pictures of the mess it is when someone drops the dash and I am wondering if there is a way to troubleshoot this problem, looking for some more simple possible fixes that I should start with first, short of removing the entire gauge.

I have no idea if the problem is the gauge itself, or cable, etc. Any advice and idea would be appreciated.

Thanks

Jim

Jim,

Hoping you have solved your problem but if not here is what I believe is best way to proceed.

The speedometer (and a tachometer) needle are driven internally by a spinning main magnet shaft; and, this shaft is driven by the cable from the transmission for speedometers. Internally speed is purely a magnetic function of how fast the shaft w/magnet is rotating. Second, the odometer function is mechanical internally but is dependent upon the magnetic shaft spinning and then a spiral gear system which turns the odometer wheels. More than likely when both needle and odometer are not working then the magnetic shaft and gears are not turning (no needle and no odometer) and is cable related. Consequently, I would first eliminate everything cable related (broken cable/bad transmission gear/cable not fully seated at attachment ends). If a broken cable, sometimes you can hear a small clicking or the needle may sporadically deflect and quickly return to zero.

If you know that the speedometer cable and transmission gear is good and cable is spinning but no needle response, then you would have a fairly significant internal gauge head problem. To me, unless you really are experienced at gauge repair, I would send it off to a professional. But, if you find the cable side bad, you repair, and your needle starts working correctly but your odometer is still not working then you have to have broken/chipped internal worm gears too. Internal worm gear failure is an extremely common issue. These worm gears can be metal or plastic or a combination of both and "reasonably" easy to replace.

Having said all this, I do not personally have experience with removing a C2 dash panel to get access to the gauges. I suspect there is no simple procedure besides patience and a lot of effort.