99 5.3 4L60E speedo freaks out tranny freaks out..not VSS

[bbchevy]

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[bbchevy]

Bought something to play with and its playing with my head. Its an interesting problem.

The Truck
99 1500 Z71
Shortbed step/style side deal
5.3
4L60E
Posi 4.10's
268,000 miles

The History...or story behind it
Engine was "replaced" at unknown mileage and has unknown mileage
Runs beautiful, powerful, and quiet
Transmission could be second or third but the truck is so clean it could almost be the first haha
Truck is pretty tight all around.
Tow haul works
Transfer case was pretty low

I've been driving the truck for about a week. Drove it 3 hours home when I bought it with no problems. Yesterday morning I checked the transfer case level again and it was a little low. So I added a little. That night drove it two miles and the speedometer started tweaking out at 30 mph. Then the trans started to freak out. Downshift then upshift to 3 then rev out then catch in third again and so on. Turned around went back. Next day tested it again and it started freaking at 20 mph the second started getting confused. So I changed the VSS (vehicle speed sensor) and it affected nothing. Totally the same.
And this all started with no warning. Bad reluctor ring or whatever it is.? It doesn't feel like its a mechanical problem as much as it is a communication issue... maybe? What's with the speedometer?

Oh and with a scan tool hooked up it records the same whack reading that the needle says. Can't isolate trans though.
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[bbchevy]

Hmmmm... someone on here has to have an idea.

Oh and for the strange chance that this could relate ( im trying to think of every odd scenario ) the day it started happening I checked the transfer case and it was empty basically. Fluid that I could wipe on my finger from the inside of the case was thicker than atf and gray. Nice. I threw some atf in there real quick. Drove it down the road later on and the speedometer freaked out and trans wouldn't work in third.

Maybe the nasty stuff got somehow sucked through the screen and dispersed onto the reluctor wheel giving it erratic reasons? Metal shavings? Can't just clean it off because I have to split the case.

Could it be?
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[clinebarger]

I responded to you in this thread http://67-72chevytrucks.com/vboard/s...d.php?t=441767

Did you check the VSS wiring? Im 90% positive you have wiring issue.

The VSS sensor sends a signal to the PCM...The PCM sends a signal to the cluster/speedo. The problem is between the VSS & PCM.

[insane04]

dont rule out throttle position sensor!

do you have access to a tech II or another scanner that will show data while you drive? you can set it up to show tps vss and vlotage at ecm to see what is changing when it acts up

[bbchevy]

Ok, so some sleepless nights gave me an idea. I was thinking about the transfer case fluid being full if metal. Vss is a magnetic pickup. Picked up metal shaving from the oil. I brake cleaned inside from the top and drained out the bottom. Left it empty (I know) and drove it down the road. Speedometer worked fine for a minute or two then started screwing up again.

The inside of the t case is just all wore out and dirty. Replaced t case. Clean gm autotrac fluid. Good to go. Shifts drives runs ... like new. All a wore out t case that was contaminated with endless metal shaving supply that would confuse the vehicle speed sensor.

I hope it helps someone in the future.

-Scott
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