th400 shifting troubles

[BRAIN]

the transmission does not want to shift out of 1st gear until about 40 mph. is there any certain
type of fluid i should use?

[AJ Johnson]

check your governor first
pull the round cup off and pull your governor, and see if the piston slides freely.
all GM trannies should use Dextron III fluid

[River Beast]

did you add a shift kit? any maintenance?

if you let off the gas before it shifts... is it like neutral?

I ask, because there are 2 bolts in the valve body that you put in finger tight until full assembly.... I cant remember the name of this part, but its got a wire off of it and a checkball under it...something to do with the shifting... like the kickdown acutator... I left it loose by mistake on a 400 YEARS ago and did the same axact thing..... I dropped the pan... tightened up the two bolts and all was fine....

[Crazy_Jeepman]

Could be a bad Modulator, I would be sure the Vac line to the Modulator is hooked up and getting Vac. Then change the Modulator if the line is hooked up. Modulator is on the Pass side, just above the front corner of the Trans Pan. Like a Vac. pot with a hose to it

[BRAIN]

yes, when i let off of the gas it coasts like i
am in neutral.

[LRRH]

check the modulator first. it is a simple check and a cheap part.

[BRAIN]

it was the vacuum hose. it was brittle and bent
in a 90 degree angle. I put a new piece of hose
on it and i can barely tell it is shifting.
it is very smooth.

THANKS FOR THE HELP!