Help! Speedometer just stopped working in my 79 L48

[madrivers1]

Hello,

Speedometer just stopped working in my 79 L48

Need help with speedometer. Just stopped working needle jumped up and down then just stopped. I changed the cable from transmissions to the cruise control transducer. Still not working! I tried hooking the end of the transmission side of the cable to a drill to spin the cable. Still nothing? OK, whets next. How can I tell if it is the cruise control transducer or the dash speedometer? By the way my Tack is working just fine.

Thank you in advance!
!:confused

 

[yellow_2002_germany]

Though there are cables connecting things together as you know, the actual speedo drive is electronic. There is a small printed circuit board attached to the back of the speedo. This could be the problem. Replacements are available from many vendors.


Disregard all of the above! It has been so long since I have owned a C3 I forgot that the PC board was on the tach, not the speedo! DUH!

 

[ironmoo]

Did you check cable from the transducer to the speedo with a drill too? If the speed works, bad transducer. They are a challenge to replace but someone with small hands can assist.
Check the back of the speedo and make sure the cable is snapped all the way in.


If all is okay, then the circuit board is next.

Good luck!

-MoO!

 

[Vettehead Mikey]

What year did GM start using electronic speedometers in C3 Corvettes? :confused

 

[madrivers1]

That was it. Why did I not think of that!

I will replace the transducer. THANKS FOR YOU HELP!

FYI,
Check out this link I found. Explains how the transducer works.

Cruise control transducer - C3 Vette Registry Forums

Did you check cable from the transducer to the speedo with a drill too? If the speed works, bad transducer. They are a challenge to replace but someone with small hands can assist.
Check the back of the speedo and make sure the cable is snapped all the way in.


If all is okay, then the circuit board is next.

Good luck!

-MoO!

 

[bill81vette]

What year did GM start using electronic speedometers in C3 Corvettes? :confused

As far as I know they are all mechanical...at least to '81,
Maybe in '82?????

 

[ironmoo]

As far as I know they are all mechanical...at least to '81,
Maybe in '82?????

Glad to hear it you found the problem. My fiancee actually replaced the transducer with me overlooking, as her hands are much smaller than mine.

1982 speedo is mechanical as well. Sorry for the confusion about the circuit board...I meant the circuit overlay that is attached to the back of the cluster.

I replaced mine recently with a 140 mph speedo. Looking at the '82 stock one on the workbench (only goes up to 85 mph), it is mechanical and the only electronics would be the circuit "sheet" that overlays the back of the speedo/tach cluster.

If you ever pull out the cluster, you may wish to check to see that there are no tears or contacts points that need cleaning on the circuit overlay. They are now pretty inexpensive to replace from several online Corvette parts dealers if you had to replace with a new one.

I cleaned my old one on all the contacts with a very light touch of a cotton swab and alcohol. Rub very lightly and take your time. The light bulbs made better contact overall and the cluster looks brighter at night.

While you are at it, replace any lens and or clean the gauge faces with a light micro cloth and water. Again rub very lightly and take your time. But it will be worth it. My gauges look brand new now!

Last thing, my new 140 speedo needle still "jumps". I heard it may be the plastic gear in the tranny worn down. I bought a new one (Ecklers has them under 10 bucks) but the '82 has a crossmember in the way and I had no leverage to spin the nuts/bolts even with the car on jacks. I'm just going to take the gear to a tranny shop and let them replace it!

Hope this helps and good luck.

-MoO!

 

[madrivers1]

I will let you know the end result.

Thanks again. Part is on back order from Ecklers. My be two weeks before I get it.I did the same procedure about 10 years ago to clean up all clear plastic lens. Yes, big difference. Next, steering wheel and new seat covers. All I did 10 years ago was swap the seats, because the passenger seat was in much better shape.