Help...any tranny techs out there??????

[roonie]

Hi.My 1990 1/2 ton has a th400.when i am slowing down to about 5 mph it feels as if my tranny fails to stay in gear.It seems as if it upshifts at this speed or like i say........fails to stay in gear.Even when i shift the lever into second gear this upshifting at slower speeds still happens.My cruise controll also does not work and i was told this could be my convertor not locking up?Does any one have an "expert" opinion on this?????????????this is a problem that is very consistant every time i slow down.

[maxwedge]

Unless some one put in a 400 I don't believe that trans would be in a 1/2 ton, check on that and post back.

[roonie]

Originally Posted by maxwedge

Unless some one put in a 400 I don't believe that trans would be in a 1/2 ton, check on that and post back.

the th400 was an option.the fellow that sold me the truck got the truck from his grandfather who bought the truck new with that option as he was using a truck camper with the truck.Now can anyone help me???thanks

[troy1]

well the th400 has a vacuum modulator on the trans if you cruise does not work I would check the vacuum lines to the cruise control unit. aslo check the vacuum line to the trans (the modulator is on the passenger side of the trans its little round can.)

[roonie]

Originally Posted by troy1

well the th400 has a vacuum modulator on the trans if you cruise does not work I would check the vacuum lines to the cruise control unit. aslo check the vacuum line to the trans (the modulator is on the passenger side of the trans its little round can.)

My cruise controll does not work on vacuum.It is all electronic in that yr truck.I am about to check my modulator tommorow.

[comp]

Originally Posted by roonie

the th400 was an option.the fellow that sold me the truck got the truck from his grandfather who bought the truck new with that option as he was using a truck camper with the truck.Now can anyone help me???thanks

you have been under it to check ????

[roonie]

Originally Posted by comp

you have been under it to check ????

It is a 3 spd auto.it is not a 700r.it has no overdrive.I have been told earlier that it has to be a th400 if it is a 3 spd.the modulator is on the passenger side.would you like the numbers off of the tag????or are you not a tranny guy and can not help me anyway.

[79403ta]

i have seen a couple of early 90 model trucks with the turbo 400 trans like stated earlier they were a special option for towing so it probably is a 400...sorry i couldnt help !!!

[supervisor1886]

Its pretty normal. Its the speed when your converter locks up. I had a 700r4 in mine with real low mlg and it was locking hard at 15 mph so I would feel a kick. No other cars would do it. Also it depends on your idle speed and ho much torque the engine pushes.
There is probably some wear on yours. Check the fluid.