Speedometer non-working at slow speed, twitches to life at higher speed. 92 C3500HD

[GM Guy]

hey guys,

dad's 92 is giving fits. the speedometer is not working at lower speeds, but get it up around 2 grand in overdrive, and she twitches to life, and seems to read accurate, but as you slow down, it twitches a bit, and then dead to the bottom.

now I assume if the stepper motor was bad, it wouldnt work at all, correct?

do VSS sensors go bad at all? I do have a Lisle GM wiring harness tool, so should I dis assemble the connector and look for corrosion, broken wires, etc, or given the symptoms, does it sound like a VSS on its way out?

all other guages are quite accurate, btw, so I dont think it is a ground issue for the cluster or harness.


any input appreciated, thanks!

 

[orrum]

Here we go . All I am qualified to advise on is them blasted grounds! Mine did that and the oil pressure gauge was also wacky and I found a ground strap that was just dangling behind the passenger fender and reconnected it and it was fixed.

 

[GM Guy]

yeah, I might go do grounds for the heck of it, as that one has never had them done. I still think it is something else, as everything else is spot on, but the speedo is wrong.

 

[THEFERMANATOR]

First thing i would do is pull the OSS and see if there is any debris on it. The output speed sensor is a magnetic type, so any metal flakes on it will cause it to go inop until the RPM's go up.

 

[GM Guy]

is it magnetic all the time, or is it an electromagnet? chips would be a very good possibility. oil hasnt been changed in that trans yet.

 

[GM Guy]

an update, it had chips on it, i cleaned it, and it still does it.

I take it replacement time? I did get a new one for it when the issue first started, so I have to use it sometime.