[Agrieve]

I did a search and I found that a lot of people were having the same issue, but not much on how to solve the problem. I have a 71 GT and the speedometer bounces between 30 and 50 while driving. I thought it was the cable at first so I replaced it and that didn't fix the issue at all. So my question is if it is the speedometer how do I fix it? and if it isn't the speedometer is it the gears on the transmission perhaps? Again how would I fix that if it were the problem.

I really appreciate everyone's help and I think this site is awesome.

 

[baz]

sounds like the clock and guess whos best to fix it
yup an auto clock fixer
man are those things fiddley inside
they work by having a disc with a magnet on that spins by the cable ,on the other side is another disc with a bit of steel and a spring so as the disc spins(cable side ) it pulls the disc needle side and gives you a speed if it bounces then it can be the spring has gone soft and this gives to much in one place so you get your 30-50 bounce
or if it goes compleatly you get an opel that does 150 as soon as you pull away
add to all this a set of gears for the oddometre and such and its best left to a pro
just dont get it wrong and get done for curbcrawling

 

[civin]

My Speedo was having some of the same problems, I replaced the cable and the speedo and used the old cable and new speedo and so forth. Nothing seemed to fix it and I was about to cut both cables and smash both speedo's. I cleaned both ends of my original cable and my original speedo, now for whatever reason it works. While it may not answer your problem don't smash it yet.

 

[nobody]

I've seen this kind of thing before. Both of the causes were easy to check. On the trannys with the 90 degree adapter if the short shaft isn't right it will bind and make the speedo jump. The later models with the plastic driven gear can get the teeth chewed up if the cable seizes up. When you replace the cable it usually works but not right. It's pretty easy to pull out the speedo driven gear and the 90 degree unit to have a look at them. I would start there since it's easy and a likely spot.