Speedometer I have a 1978 Corvette 350 automatic. Purchase new 40 years ago. The speedometer has stopped working. I had the seals changed in the tra

[jack hanna]

I have a 1978 Corvette 350 automatic.
Purchase new 40 years ago. The speedometer has stopped working. I had the seals changed in the transmission this spring as was leaking oil. The cable etc was good at that end. I think it could be in the unit that is on the left side of the engine (drivers side) near firewall. There a second cable that extends from that little unit (Maybe called regulator? Correct name unknown) to the speedometer. The wire leads from the unit also goes to cruise control. The cruise is not working.
How do I determine the problem and if needed obtain a replacement unit?
Thank you in advance for any assistance.
[email protected]

 

[XFIRE82]

Unscrew both cables from the cruise unit called a transducer . Now with fingers you should be able to spin the cable that goes to the dash , if you got someone there to look at the speedo and see if the needle moves , if it does then that cable is ok. Now the cable that goes to the tranny should be not possible to turn , if it does then the cable is broken or stripped end , or the plastic gear in the tranny is stripped. One last is see if you can spin the shaft on the cruise unit....they both should turn when you spin either one, if don't spin then the cruise is seized thus no speedo .

 

[Paul 06 vette]

This is a great site for all years of corvette help. It’s good that there is so many knowledgeable people

 

[Rruuff Day]

Unscrew both cables from the cruise unit called a transducer . Now with fingers you should be able to spin the cable that goes to the dash , if you got someone there to look at the speedo and see if the needle moves , if it does then that cable is ok. Now the cable that goes to the tranny should be not possible to turn , if it does then the cable is broken or stripped end , or the plastic gear in the tranny is stripped. One last is see if you can spin the shaft on the cruise unit....they both should turn when you spin either one, if don't spin then the cruise is seized thus no speedo .

Excellent Michael. It's the members, the knowledge and the willingness to share that knowledge that makes this forum rock like no other.

 

[jack hanna]

THANK YOU! Jack

 

[jack hanna]

THANK YOU !
Jack

 

[jack hanna]

Thank you for the information. The speedometer works with drill on cable from the transducer to speedometer.
I cannot grasp the inner cable from the transmission. However the inner cable to the speedometer at the transducer does not have any attachment on the end? I believe there should be?
If there is supposed to be a tip on end it may still be in the transducer, dissolved or fell off when I was struggling to disconnect the cable? Can I replace the tip? Do I need to try and feed a new cable without disconnecting the cable under the dash?
[email protected]

 

[XFIRE82]

It can vary as I have seen different cable ends over the years. The cable end may be just shaped in a square , or it can be a glued on plastic square tip . Same thing with the cable removal from the casing , some simply pull out this end or it may be the other end or not at all if both ends have glued on tips. It is not hard to tell if it will pull out of the casing at the transducer end by simply grabbing it with a pair of sharp nose pliers and pull, if you feel right away a " dead end " just try push it in and out and you can tell if the cable is moving free and has a stopper hit to it. If it does then have to try pull from the other side. Replacement of the tip is possible if the cable did not break off and there is enough left to glue back on . Did you try and see if the transducer turns ? Good practice is to pull the cable out once in a blue moon and soak it in engine or auto tranny oil and put back in the casing as this keeps it lubed and a smooth turning speedo.

 

[Cadder61]

At one time, GM marketed a universal speedo cable- long length of inner cable with one end crimped square. You inserted into outer cable, figure out the length you actually needed and cut the cable. A plastic tip was then glued onto the cut end with hot melt glue. Those plastic ends quite often came off if not done properly. These kits have probably long since been discontinued, but I wonder if the jobbers might carry something similar? If memory serves (and it's been 20 years since I was in the parts business) original factory cables had both ends crimped square as they were made for specific applications.
I might add those cruise transducers were a headache as well. Often seized up and destroyed cable ends, or just generally quit working. And they were expensive - over 200.00 in 1980's dollars. More than one customer decided he didn't need cruise control that badly and got a different lower cable with female end that the upper could screw on to and bypass the whole thing...