M1008 TH400 Shift Issue

[sgreen2]

My newly aquired M1008 would not shift out of 1st gear. I researched the -20 and -34 manuals. I performed the first step listed in the -34; I unplugged the downshift electrical connector from the drivers side of the transmission and then operated the M1008 to check shifting points. It seemed to upshift ok with the downshift connector unplugged. The manual says to replace the transmission downshift switch at the gas pedal bracket if this was the cause. I have three questions.

1) Will it hurt to operate the M1008 without the downshift being hooked up (kickback)?

2) Where can I get the switch that is located on the gas pedal bracket. I have been unable to find one online.

3) Should I check anything else even though this seemed to fix the problem? The vacuum hoses seem to be in good shape.

 

[niferous]

Would it not shift at all or did it just take forever to do so? How fast did you get the truck up to?

Have you ever replaced your vacuum hose? Have you checked the vacuum valve in the side of the transmission and the vacuum line that goes between the metal line and valve?

 

[sgreen2]

It would not shift at all. I got the truck up to about 25 as I did not want to take it further cause the engine sounded like it was all reved out at that speed.

I did not replace my vacuum line because it looked to be free from cracks or other damage. Also, I did not check the vacuum valve since the disconnecting of the downshift electrical connector seemed to fix the problem and the truck shifted ok once that was done.

 

[Warthog]

Looking at the TM 9-2320-289-34P parts manual, Figure 49, item #11, the GM part number is

1242101 - SWITCH, DOWN SHIFT TRNS S/SHIFT

Napa doesn't show it as a cross reference but RockAuto does

ACDELCO Part # 1242101


Running the truck without the switch hooked up will not hurt anything, It only comes into effect when you are really accelerating.

 

[niferous]

http://www.steelsoldiers.com/cucv/45198-hard-shifting-still-after-repairs.html