Speedometer broken...

[K10Scottsdale78]

I bought my truck with the speedometer not working. I assumed it would just be a cable, so I put a new one in and it still doesn't work. Could it be the entire unit thats shot?

I talked to a guy on craigslist thats willing to sell me one out of a mid 80s K20 that hes about to scrap. His works, but im not sure if it would be compatible in my 1978... Since my speedo goes to 100 mph, and the late 80s one goes up to 85 mph. Would that one fit in mine and give an accurate speed???

[demok83]

I had this same problem in my truck. I thought it was just the speedometer cable, but it wasn't. The gear inside my transmission was faulty. Running like a charm now. You can check to see if your speedometer is working by disconnecting it from your transmission, and tightening down on the cable with a cordless drill. When you clamp down on it, make it spin in reverse and have someone watch the speedometer to see if it moves. If it does, then your cable and speedometer are both good. I would check that before I buy a new speedometer.

[K10Scottsdale78]

Ill have to give that a try this week and see if that does the trick. I wish I knew that before I cut the old speedo cable because I was in a hurry to get the new one in! good thing I only paid 12 bucks for the new one!! Im hoping thats all the problem is, I dont wanna pay much money for a new gauge off of ebay...