I want to order a replacement speedo cable to fix my bouncing speedo needle but Ecklers had 4 different ones listed. My car is an auto tranny so does it have upper and lower cables or just a one piece speedo cable? If it has upper/lower, which one should I replace to fix the bouncing problem? Thanks

 

Lube the one you have and see if that gets rid of the bounce.

 

As far as I know the upper and lower only goes with Cruise Control. Do you have that? Also if it's bouncing that doesn't have to mean it's the cable. Start with do you have Cruise? WELL DO YOU? (can't help it, been a long day and i gots ta have me some fun)

 

Cruise control Vettes have an upper and lower speedometer cable. Non cruise control has one cable from the trans to the speedometer. But look at other things first...lube the cable. If you have cruise control it could be in the transducer (cruise control mechanism under the brake master cylinder).

 

The '72 automatic model had 2 cables that just screw together with a coupling under the car....no cruise was available (although I always suspected one was intended as an option and never got approved until years later). The only suggestion I have for you is to remove the connector at the transmission and try to spin the cable end with your fingers to determine which direction gets a reading on the speedo (I can never remember which it is and you don't want to run it backward). Then hook the cable end into the chuck of a cordless variable speed drill and run at slow speed to see if the reading is stable (or if it bounces). Then move to the junction connector under the car and do the same thing on the end of the second cable. If it is similarly bouncy on both cable tests, chances are the downstream [second] cable is your problem. If you get the bounces with both cables connected and no bounce with just the second cable, the first cable is your problem. Unfortunately, one (or both) of the cables can be defective...and, if bad enough for long enough, the cable housing can be damaged also. Now, you can also remove the cable from the tranny cable to look it over and see if rubbing on the casing is present. If that one looks good, just put a LIGHT rub of grease on the cable except at the ends, reinstall and try again. It might just be "dry". To remove the upper cable, you have to remove it from the speedo end. (bummer) P.S. With 30+ year old hardware, if you replace one of the cables, replace them both...don't be 'penny foolish'.

 

thanks, I'll give this a try with the drill to isolate the problem

 

Mine did the same thing with the bouncing. What it ended up being was the cable gear at the tranny. It had five teeth broken on it. Thing is, they were broken at different places and I couldn't figure that one out.
My bud Mark got out a mike (sp) and showed me on the lower cable tranny gear that there was a difference on the shaft of 1/32" on the gear side from the cable side. The gear side is where the gear rides and gets worn.
He said there's only about 1/16" of contact in the cable gear and the tranny gear and that the 1/32" allows enough for the cable gear to bounce causing the speedo to bounce and the teeth to not make correct contact and breaking them. That's why mine were broken in different places on the gear instead of in a row.
But, I didn't do like 71 said and replace everything else, (dumb move on my part) and about a week later the speedo went out again. Only this time I didn't get a "warning" like the bounce, it just dropped.
Haven't had time to go back on the rack, so at this point I don't have a clue what's broke. We'll see.