HELP! TH400 wont go into 3rd gear ??

BustedPinion · Feb 10, 2007

*UPDATE* TH400 wont go into 3rd gear ??

Just got a used 78' K20, has a th400/203. I already know the 203 growls in 4-HI.. when i got it and drove it over an hour home it shifted kinda hard (prolly because the vacume line & modulator input are plugged with mud

) but shifted good everytime..

I just went to go to the store and no matter what i couldnt get it to hit 3rd gear RPM's just scream in 2nd.. I dont see any wires coming off it so i dont think i have one of those lockups???

TreeClimber · Feb 10, 2007

Take it out of 4 low

(My dad had me come out and fix his once, same problem)

And check your vacume hose to make sure it didn't pop off the vacume modulator and/or off the engine vacume supply source

benw1 · Feb 10, 2007

I had the same problem once, replaced the modulator to fix it.

TreeClimber · Feb 10, 2007

BustedPinion said:
. I dont see any wires coming off it so i dont think i have one of those lockups???

It isn't a lockup, but you should still have a wire coming from the pedal to the kickdown solinoid on the drivers side. However the T/C isn't a lockup.

And I still think someone bumped the lever into low range

BustedPinion · Feb 10, 2007

i think its the mod maybe, i pulled it and cleaned the mus out, and found the adjustable screw was all the way out

also it has 2 tiny rusted out holes. found that after trying to clean the muss out. I'll replace tommorrow and update. the only thing ive ever had those do when shot was make it shift hard..

anyone else ever have one KEPP it from shifting? :wtf:

junkyard jim · Feb 10, 2007

Yup. Vacuum leak makes for a bad upshift. Check the pin inside isn't bent too.

benw1 · Feb 11, 2007

BustedPinion said:
i think its the mod maybe, i pulled it and cleaned the mus out, and found the adjustable screw was all the way out also it has 2 tiny rusted out holes. found that after trying to clean the muss out. I'll replace tommorrow and update. the only thing ive ever had those do when shot was make it shift hard..

anyone else ever have one KEPP it from shifting? :wtf:

Yes, I had the same problem once, replaced the modulator to fix it.