98 Gmc Transmission Concerns

hott327z71 · March 21, 2011

I have a 98 GMC Sierra Z71 with 123,xxx miles. 5.7 350. All original, just replaced the intake manifold gasket, plugs, wires, cap & rotar. truck runs great and gets 17 mpg.

When shifting into any forward gear it takes about 4 seconds to engage and shifts hard right away in the morning. Also it shifts from 1st to second relativly hard, this will sometimes goes away, its not always. Fluid looks great and doesnt smell and at correct levels.

jwhuber · March 22, 2011

So what are you asking? Why it shifts the way it does?

Could be the TPS (throttle position sensor)

cliobogger · March 22, 2011

could be the tps, or you may need a new tranny if its the original.

hott327z71 · March 22, 2011

Wondering why it takes so long to engage, I heard it could be in the "valve system" its not filling with enough tranny fluid??

the transmission works excellant other than these issues, it shifts without a beat and very smooth in all other gears except into 1st which is right away. I think its something simple rather than the transmission going bad.

Mike G · March 29, 2011

I am no trans expert, but... Your slow engagement problem is first thing in the day, correct. This would indicate a problem with the pump or the torque converter. Then you have a shift issue, this would relate to the valve body, my guess may be a sticky slider. No problems once the motor/trans warm up, correct? You may try running some cleaner through then flushing it out and putting new fluid with a conditioner.

--Mike

ChevyTech77 · March 29, 2011

Have the transmission fluid pressures checked, by a trans tech, when the concern is present. Weak pump, internally loose convertor or possible valve body issue.

My '98 may shift just a bit hard 1-2 in the morning but has never had a delayed engaugement. Just took mine apart a few months ago with 197k on the clock and it looked beautiful inside. Replaced the reaction shell (drive hub starting to crack) and noisy torque convertor (howl/droan noise in park in real cold temps) and it's still working just fine. I flush mine once a year and change the filter out every other flush though, sense I bought it with 87k on it in '04. Plus, I never haul/tow anything in OD.