1989 Chevrolet Silverado
5.7 Engine
700-R4 Transmission - Auto

I am having problems with my speedometer not working properly. It will normally work the first thing each morning and within a distance of 15 miles during stops it will stop working. Normally it will start back at a random time during the day. Seems to be more issues if the weather is extremely hot. I can tap on the left side of the speedometer cluster housing (with the dash bezel off) and the speedometer will start working. I have had the cluster completely gone through by a professional company; I have replaced the speedometer gauge and have replaced the speed sensor on the transmission. I have also sprayed all connections with CRC contact cleaner. If I can find someone with an OBD-1, will this provide any troubleshooting for the speedometer? Any suggestions? Thanks

Greg

 

I do not believe an ODB-1 code reader will help at all in diagnosing this issue. Sounds to me like intermittent connectivity. I've not been into the dash of a 1989, but on my 1996 C1500, the instrument cluster plugs into a flex circuit connector in the dash, which is where I would suspect the most likely issue is, if tapping on things brings it back. If you've had the instrument cluster rebuilt, then that connection between it and the truck would be the next thing to check. Just examine all contacts on that and the back of the instrument cluster carefully.

I love my old GMT400, but feel that wiring and electrical issues are one of the bigger problems facing us owners of these old trucks. I cannot tell you HOW many times I've replaced the blower speed control, as GM stupidly routes ALL power for the blower through a simple switch, which heats up and burns up over time.

 

My 1995 has a sender mounted on Transfer case that went bad. I replaced and speedometer problem went away. You problem sound like heat is causing wiring issues. Start wiggling wires.