Took the '70 out for a short drive and the speedometer starts going wild. Up to about 30 MPH its OK, above that it starts to whine and the needle jumps all over. The whine is coming our of the speedometer. Is it the cable or is the speedometer terminal?

 

OH me, I have answered about how exactly I have fixed my own on other threads, somewhere it need archived...but I don't know how to do that....

so....

pull the dash...have fun.....it's a BITCH!!!!

then take the speedo out of the shell, carelully on the kitchen table under a bright light.....you will need it...

we are working on a fragile instrument here, and any dust and trash in the system there will make it fail again...

so after having the naked mechanism in your hand, carefully take your thumb and index finger , pull the needle off the tach, straight up...do NOT PRY>>>>>>

it should snap up and off with no sweat....
then take mph face card off....Radio shak screwdriver assortment...
then take brackets off, under them you will find a vaguely horseshoe shaped loop that goes over top of the indicator output shaft, and the 'calrod' looking coil spring, which is VERY fragile... to an aluminum cup...which is going over a spinning magnet attached to the input bearing/shaft arrangement....
well there is a pin sized top bearing and of course the input shaft bearings...
I use WD40, just a smidge off a Q tip or screwdriver blade to refresh the oil in ALL those bearings....
reassemble as originally....

ME, I"d attach it to the speedo cable and go for a ride with it hanging free...see if it's indicatiog well.....

of course it could be a cable from the tranny, but these cars are so old now the chances of that fixing it for very long are allmost nil....

GENE

 

Try lubing the cable. That is normally the cause of jumping, noisey speedometers. Sometimes you have to replace the cable and housing. :chevy

 

I had a similar problem with the speedo of my '81 yesterday and posted a question about it on this board. I lubed the speedo cable from the tranny with engine oil. Solved my problem but got advised to use some grease instead.

Hope this helps

Roger

 

I didn't find the cure but I was able to clear up the symptom. This darn cold weather in Michigan is the problem. It looks like a cold speedometer was the cause. I let the interior heat up, with the help of a hair dryer, and the problem went away. Thanks to all who had ideas on how to help me.