Bouncing speedometer
Thread Starter
Safety Car
Joined: Nov 2008
Posts: 4,368
Likes: 9
From: Colorado
Bouncing speedometer
'79 corvette and my speedometer died many years ago. 6 years ago or so I lubed the cables (cruise control) with WD40, yeah it's a no no but I did. I chucked the upper inner cable in a drill and ran it in reverse for awhile and the speedometer came back to life and has worked great. Last weekend on open deserted interstate I ran up to 110 - 120mph or so, the needle was bouncing. Now when I am at 40 mph it will suddenly swing up to 50-60 and back down, particularly large swings on deceleration and low speed reads zero. I've shot some WD40 into the upper cable but haven't had a chance to test it but I am wondering if I can get my hand up behind the speedometer to detach the upper and replace or really lube it. I really don't want to pull the gauges out and I know from years past this has been discussed at least, but I can't find the threads I saw yrs ago. Might have to find a rent-a-kid to reach the cable I guess
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
The cable is binding in the outer sheath as it turns. This imparts a whipping action that can damage the mechanism in the speedo head. The cable is "toast" and needs to be replaced. If you have a two-piece cable, it would be best to replace it with the same setup; one long cable has higher probability of whipping as well.
That may or may not fix the speedo head issue, but it certainly needs to be done BEFORE the head is repaired or replaced. Otherwise, you would create the same problem again.
That may or may not fix the speedo head issue, but it certainly needs to be done BEFORE the head is repaired or replaced. Otherwise, you would create the same problem again.
Drifting
Joined: Sep 2010
Posts: 1,412
Likes: 50
From: Laguna Niguel California
Sometimes lubing or replacing the cable will help, sometimes not. I recently had the cable replaced because it broke but the speedo stiil bounces. Face it, how much can we expect from these 40 year old dinosaurs? Don't get me wrong, I still don't want to drive anything else.
Thread Starter
Safety Car
Joined: Nov 2008
Posts: 4,368
Likes: 9
From: Colorado
I had enough time over the lunch break to run home, lube the cables, run the upper in a drill going in reverse and do a very short test drive. It all semed ok, certainly improved if not 100%, every drive will `be a test at this point. Where is a good set of instructions on changing out the upper cable? I know I've seen some good pointers in the past, ( I wasn't kidding about finding a "rent-a-kid" to possibly reach the cable from behind. I know if I pull the cluster out I'll have enough "while I'm at it chores" that it could ruin the summer driving time 
I used to pull the cable off a '63 chevy so parents couldn't check the odometer all the time
but the vette isn't that accessible.
I used to pull the cable off a '63 chevy so parents couldn't check the odometer all the time
but the vette isn't that accessible.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Changing the cable is easy. There is a 'push-to-release' clip on the entry point to the speedo head. You push the clip on both sides of the cable to release it. Then, while pressing, you just pull the cable out. You need to insert the speedo head end of the cable first when installing the new one, so that you can turn the cable to get it engaged with the speedo head.
The only real problems are that you have to lay on your back to work with the speedo head, and fische the cable through the firewall.
The only real problems are that you have to lay on your back to work with the speedo head, and fische the cable through the firewall.
Thread Starter
Safety Car
Joined: Nov 2008
Posts: 4,368
Likes: 9
From: Colorado
I imagine the seat removed as well as lower steering column cover and the air duct in the area for access? I think it's ok for now but it's snowing so I can't go for a run for a few days is my guess, thanks for the info though.
