2003 GMC 1-2 shift issues

Discussion in 'Transmission & Transfer Case' started by knucklehead, Dec 2, 2016.

  1. knucklehead

    knucklehead New Member

    Joined:
    Dec 2, 2016
    Messages:
    3
    When i got this vehicle a couple years ago, the 1-2 and 2-3 shifts were long and drawn out. i babied it for a while and then decided to rebuild it. the reverse input drum surface was a total mess where the band was so i replaced that and both sprags as hard part replacements. I also installed pinless accumulators in the 1-2 housing and forward housing, replaced the 1-2 accumulator valve line with the updated GM part, .490 boost valve, and installed the Transgo SK kit in the valve body, blocking off the 4th accumulator for a nice 4th gear apply. New TG separator plate drilled per TG instructions and a corvette (093) servo. I only have problems now with the 1-2 shift. Vehicle has 145k miles on it and had already been "rebuilt" once. It has 4 pinion planets in it for some reason - my guess is that whoever rebuilt it before pulled the 5 pinion planets out to sell on ebay (probably how I got my set for my other trans rebuild, lol!) Anyway, at part throttle (normal driving) the 1-2 shift is delayed and then shifts hard. all other shifts are nice, quick, and firm but not harsh. I currently have my pressure gauge hooked up to the test port. i don't have a lot of data yet to provide from the gauge due to trying to drive while watching the gauge - I watched the road, not the gauge, lol!. I bought rebuilt valve bodies for my previous rebuilds, but wanted to try my hand at it on this one. any suggestions? My guess is that whatever is causing this is also responsible for wearing out the reverse input drum. Any/all input is appreciated!!!
     
    Last edited: Dec 2, 2016
  2. knucklehead

    knucklehead New Member

    Joined:
    Dec 2, 2016
    Messages:
    3
    Just drove it while watching the gauge. At stop in drive, 75 psi. Pressure rises quickly to about 150, but then drops to about 110 before rising again to 120 and then it shifts to 2nd gear. I should note additionally that I had read to use the stock springs in the 1-2 housing rather than the springs from the TG kit and I did not add a gold spacer ring in the servo. Seems to me that the spacer ring would prevent the pin from fully engaging the band.