apwatson50

so recently my speedometer has started "bouncing" then sometimes just read zero until just the right bump it will read then back to zero. I put a new generator on the t-case, seemed to work for a while but it has continued.

Noticed, when the speedo quits, so does the odometer. BUT the cruise still works. So if the cruise works, the signal generator must be working right?

So I am thinking there must be a loose corroded power or ground wire to the speedo head unit. Does everyone concur?

thanks for the help, Aaron

Mark Nixon

You're thinking correctly.
Never seen the cruise work and had no speedo, unless the speedo board is bad.

My old '91 flatbed has an issue where it quits counting miles if it's below 60 degrees in the cab, yet the cruise and speedo will work.
It's spooky to see the miles start working 20+ miles into a trip.

Mark.

GIT-R-DONE

Ya, check over the wires to make sure your not grounding out, OR, needing more ground. I had one that I had to install and extra ground wire TO the ground for the VSS. Worked for a while....

Crossy's son

My VSS plug was hosed up, and everytime i rained my speedo would bounce around.

apwatson50

Well it definitely seems weather dependent. Cold hardly works, warmed up seems to work pretty good still maybe bounces a little when hitting bumps.

I did when I put the new VSS in, I cut the old plug off and soldered in the new plug that came with the VSS, hoping it was just the plug.

I will have to pull the cluster out to check power and grounds.

Onemoparnut

I would bet that it is in the cluster or wiring between pcm and the cluster. If it was between the vss and the pcm then the cruise would act up when the speedometer acts up.

layapipe

have a 1991 & 1992 727 3 speed & 4 speed over. speed ometer shows speed but does not add miles any ideas. installed new trans speed drives and replaced speedos. but same results

apwatson50

so as an update I removed the gauge cluster, soldered a wire to the ground on the cluster and put a self tapping screw into the metal behind the cluster. Since then the needle has been rock solid. That has been a few months.

12valvin

Did the odometer start working?

apwatson50

yep everything did.

12valvin

Where exactly did you solder the wire too?

apwatson50

If you look is some of Jim Lane's threads about putting LED lights in the gauge cluster, you will see where to put the wire.

Basically I figured out which wire was the ground, in the original harness, then I soldered a wire to the circuit board next to that wire.