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93 K2500 speedo jumping around update, fixed see post #8

rick88blaze

rick88blaze

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Knob Noster, Mo.
The speedo is jumping around on my tow rig. As soon as I start moving it jumps up anywhere from 20 to 50 and when I'm going down the road it pegs out. The tranny is shifting fine and I changed out the VSS and I still have the same problem. Anyone have any ideas?

The truck has a 350TBI/4L60E/241 drivetrain.

Thanks in advance,
Rick
 
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rick88blaze said:
The speedo is jumping around on my tow rig. As soon as I start moving it jumps up anywhere from 20 to 50 and when I'm going down the road it pegs out. The tranny is shifting fine and I changed out the VSS and I still have the same problem. Anyone have any ideas?

The truck has a 350TBI/4L60E/241 drivetrain.

Thanks in advance,
Rick
Click to expand...

I too changed out the VSS when i had this problem. Mine was mainly after the truck had warmed up and had been on the freeway for a while. The issue ended up being the twisted pair wire connecting the VSS into the trans harness. The insulation was cooked, and it was shorting at almost every twist :doah:

Looked fine at first, until i untwisted it and figured out how bad it was.

Cut the ends off, spliced in a new section of wire, and reinstalled.

No issues in 2 yrs!
 
Sweet, I'll go check out the wires.

It worked fine up until yesterday afternoon. I was heading down the highway and it worked fine, I got off the highway to head to Autozone and when I looked down to check my speed it said I was doing 70. It started doing it out of the blue yesterday.
 
Ok, so I've checked all the wires down by the tranny and I couldn't find any shorts down there. I did try something else though. I unhooked the connector from the VSS and when I started the truck the speedo shoots up on it's own. When I revved the engine up the speedo sped up. I did some research and read up on the VSS buffer. Is there a chance that it went bad?
 
rick88blaze said:
Ok, so I've checked all the wires down by the tranny and I couldn't find any shorts down there. I did try something else though. I unhooked the connector from the VSS and when I started the truck the speedo shoots up on it's own. When I revved the engine up the speedo sped up. I did some research and read up on the VSS buffer. Is there a chance that it went bad?
Click to expand...


NO idea about that . But, i'd pull the VSS harness thing i talked about, and inspect it out of the truck.

If you remove the VSS, and the wires are shorting still, it could do what you are saying still.
 
I'll pull it and check it out. I will go pick up some new wire before I pull it that way I can go ahead and replace it while I've got it apart. Thanks for the help.

I'll update this as I find things out.
 
Ok, so the wires are replaced and it's still acting up. I talked to a couple friends that are GM mechanics and they are both pretty sure the speedometer is shot.

Anyone know of a good place to get my instrument panel repaired? Or does anyone on here know how to do it?
 
Disregard all of the above. For some reason GM ran the ground for the speedometer from down by the T-case back up to the thermostat housing. I tightened the top nut down on it and wouldn't you know it, the speedo works just fine now. All this crap just to find out a nut came loose. What a bunch of crap! Oh well, it's fixed now!
Rick
 
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