My speedometer on my 79 used to jump around like crazy> If you were doing 30, it would go to 30,60, 40 never being accurate, the needle always jumped around. Now it quit working all together. Could it be the speedometer itself, or some other issue?

 

I’m watching this because I changed my speedometer cable and it still bounces around….

 

I was going to suggest looking at the routing of the cable as any powerful bend will cause some craziness. Sounds like you did that though.

 

My advice is send the speedo to a reputable repair shop. You only want to remove the speedo/dash one time. On my 73 convertible removing and reinstalling the speedo/tach was the worst repair that I ever did on my car. The large wiring harness rides on top of the speedo / tach and after 50 years the wires are like Steel, what a F ing nightmare.

 

i really hate to rip into the dash unless I'm sure. I know any of that is a nightmare! Plus now it quit working completely!

 

Did you hear any clicking noises when it was bouncing? Mine started clicking when the speedometer jumped. I had a stripped out gear that drives the odometer.

 

Reach your hand up behind gauges and check that it's clipped in correctly.
Under the car, check where it connects into the speedo sender. Unscrew and remove the gear holder and check both gears for missing teeth.

 

I didn't really remember a clicking noise. It just bounced erratically, did your mileage stop registering to? Mine did. I will reach up in there and see if it is connected, I did disconnect it from the transmission, and everything looked ok!

 

Check the easy end first. Remove the locking clip at the transmission and unscrew the cable.
Might be a little piece of plastic tip there, might not. The plastic is a shear (pin) piece. Its easier to replace than the speedo cluster.

All indications are that the cable sheath or cover has not been lubed since '79. That's why they start to jump, eventually snap.
Have a helper sit behind the wheel while you spin the cable under the car with your electric drill. If the needle does not move, try the other direction.
If the needle still doesn't move, the issue is in the cluster

 

One step at a time.
Grease the cable first. Thats the easiest repair and a probable cause for your issues. As someone else said, make sure you have no hard bends.
If that doesn't work then check the gear at the transmission, thats the next accessible area.
Lastly, bring the speed to a speedo shop...... Hopefully you won't get to this part.

 

Bouncing is generally 1 of 2 things. The cable is binding up. Or the speedo it's self is binding up.
Then it stopped! The cable broke or the speedo died.
Start by checking the cable.
These types of repairs ALWAYS mean pulling the dash.
Best of luck.

 

I sent my 82 unit to John and he converted it to. 140 mph! Great to work with. I highly recommend him


John & Tammy Dvorski
Redline Gauge & Clock Repair
3427 W. Cedar Lake Rd.
Greenbush, MI 48738
731-571-0766
www.redlineg.com

 

Thanks for all the replies! I will start at the easy part first, then work up. I will keep you posted on how it goes! Thanks to all again!

 

Larr,

If you have Cruise Control you will have a shorter cable from tranny to the transducer which is near the drivers inner fender.
Then another short cable from there through the firewall.
C.C. are two-piece cables. W/o cruise, one long unit.

Those transducers can jam up from age and snap the inner cable. If the Cruise does not work anyway, you by-pass it by purchasing a longer cable.

 

Yes I do have cruise control, it does work, but it kind of speeds up and keeps going it won't adjust to the speed you set it at, it just takes off!

 

When I first bought my Vette, I noticed half the Cruise parts were missing and I was not about to replace.
When the speedo got a little twitchy I went ahead and by-passed the C.C with a longer cable.

Usually when buying speedo cables they are listed with four options:
4-speed, w/o cruise
4-speed w/cruise
auto w/o cruise
auto w/ cruise

And all cruise cables will list as "upper or lower" cable.

If you do end up swapping the one through the firewall to the cluster, have a helper standing by with the new cable. As you disconnect the old from the back of the cluster, your helper should pull the old out and feed you the new. Not a fun job by yourself laying under the dash.

 

Tape new one to the old one. Pull it through and pull the new cable with it. No helper needed.

 

When my Speedometer started bouncing a bit I removed the cable from down below and spun the inner cable with an electric drill. While spinning with the drill it was smooth and the speedometer worked fine. I then used Graphite powder to lubricate the cable and it worked great. I was hesitant to use any grease for fear that it would cause drag when cold and hard.

My speedometer was rebuilt by a guy who goes to Corvettes@Carlisle where I first met him. It was important to me to keep things right for the 1968 Corvette as the 1968 Speedometer and tachometer use a different color in the background. I wanted the original unit back in the car as quickly as I could with the proper color background to match

Lubricating the Tach cable is also another good place to use the graphite cable lube. When I first removed my tach cable I was surprised at the old grease and junk on the cable. I used Brake Clean and cleaned the cable inside and out before letting it dry and then applying the graphite.

Motor Cycle mechanics are frequently very independent guys and rarely ask for help as they can do most of it themselves. They are frequently very creative mechanics and figure solutions on the way.

 

Ok this is what I found, I disconnected it from the transmission and spun it with a drill. It did nothing. I took it off the cruise control where it goes into the car and turned it by hand and the speedometer worked. Is it something in the cruise control? If so does it need to be rebuilt? Thanks!

 

Could be the cruise control or the lower cable is shot. i would disconnect from tranny and cc and spin cable from either end and see if the opposite end is turning - if not your lower cable is broken.
Pat