300 miles from home and tranny wouldn't shift

[cdivine]

There I was, cruising in my 95 K1500 on my way to pick up a clean 94 Suburban. About 20min from the destination my speedometer dropped to 0. Got off the hwy and tranny wouldn't shift out of 2nd but speedo started working. Arrived at the spot, paid the man and rolled out. Tranny shifting fine after the truck sat for 15min.

Once more on the way back speedo quit, stayed in OD until I got off the hwy. Shut truck off for 1min and got my gears back. RPM never quit and never lost gear indicator light.

So I know this could be a speed sensor or ignition switch but to my knowledge it shouldn't be ignition switch because I never lost RPM. I figured I'd just throw a new sensor in until I saw the price. Figured I'd make a post first and get some input.

 

[HotWheelsBurban]

There I was, cruising in my 95 K1500 on my way to pick up a clean 94 Suburban. About 20min from the destination my speedometer dropped to 0. Got off the hwy and tranny wouldn't shift out of 2nd but speedo started working. Arrived at the spot, paid the man and rolled out. Tranny shifting fine after the truck sat for 15min.

Once more on the way back speedo quit, stayed in OD until I got off the hwy. Shut truck off for 1min and got my gears back. RPM never quit and never lost gear indicator light.

So I know this could be a speed sensor or ignition switch but to my knowledge it shouldn't be ignition switch because I never lost RPM. I figured I'd just throw a new sensor in until I saw the price. Figured I'd make a post first and get some input.

What does the fluid level look like (correct or low)? What color is it (bright red, burnt red/brown, smells like burnt oil)?

 

[cdivine]

What does the fluid level look like (correct or low)? What color is it (bright red, burnt red/brown, smells like burnt oil)?

Fluid is good all around. Never had a problem on this tranny. Which is why it's a bit weird to me on a long trip like this is started acting up. Never got hot either according to my gauge.

 

[1997]

your 95 (OBD1) can set codes without the check engine light coming on.
check to see if a code(s) has been set.

 

[NickTransmissions]

Fluid is good all around. Never had a problem on this tranny. Which is why it's a bit weird to me on a long trip like this is started acting up. Never got hot either according to my gauge.

You're correct. Replace the VSS if its plugged in. Bad vss = no upshift from first gear

 

[GrimsterGMC]

Ain't it just grand having all of this combined knowledge just a keyboard away. I love this forum.

 

[Schurkey]

When MY speedo in the '88 K1500 went wonky, it had nothing to do with the VSS. The entire problem was the DRAC module in the instrument cluster going intermittent. In that the '88 had a 700-R4, I only lost the converter clutch, not various gears. Also lost cruise control and ABS, all of that relies on a signal from the DRAC.

I don't know where the DRAC is on a '95. Perhaps integrated into the computer.

 

[NickTransmissions]

When MY speedo in the '88 K1500 went wonky, it had nothing to do with the VSS. The entire problem was the DRAC module in the instrument cluster going intermittent. In that the '88 had a 700-R4, I only lost the converter clutch, not various gears. Also lost cruise control and ABS, all of that relies on a signal from the DRAC.

I don't know where the DRAC is on a '95. Perhaps integrated into the computer.

The 700R4s used a mechanical speedo gear set/cable (on some very late models, there were electromechanical) however all shifting was managed/controlled mechanically by the governor which worked independently of the speedometer system whereas the next gen 4speeds (60/80) the ecm required the vss to be working before it would enable upshifts which is his problem.

 

[Schurkey]

The 700R4s used a mechanical speedo gear set/cable (on some very late models, there were electromechanical)

Mine had a VSS crammed into the transfer case.

Point is, "speedo dead and no upshifts" can be something OTHER than the VSS. Don't replace it "just because". Diagnose first, replace later. This could be a failed wire harness, failed DRAC, failed VSS...and probably some other issues as well.

 

[NickTransmissions]

Mine had a VSS crammed into the transfer case.

Point is, "speedo dead and no upshifts" can be something OTHER than the VSS. Don't replace it "just because". Diagnose first, replace later. This could be a failed wire harness, failed DRAC, failed VSS...and probably some other issues as well.

Sure, it could be those other things. But the likelihood is very low, esp given it was working then suddenly its not. If the ecm isnt receiving the vss signal, there's no upshifts. He can certainly check the vss harness for faults/shorts etc to rule those out or scan the ECM but more than likely its the vss.

I keep a spare VSS and mlps in my vehicles just in case as they are the most likely failure points when either no upshift or no crank no start conditions respectively, arise