need to find out what are common causes of third gear being weak in the old th350 trannies

it will go into third but its weak usually, slips noticeably, almost all the time, but not always, sometimes its ok, up to a certain RPM then its gone


fluid is nice bright red and smells like new,

ive tried runnign with and without the cable connected -but with no change at all,

and the mod valve i replaced- but again with no change

also it had an aftermarket oil cooler in front of the radiator, i removed that and connected the trans directly to the radiator- also with no change

what can be wrong ?

i have a hard time beliving it is anything major and that it needs a rebuild or anything, because it runs awesome all except for this little quirk

what can i try/check ?

anything without having to remove the tranny from the truck ?

i was told it was rebuilt roughly almost 5 years ago or so, maybe a little less and its painted blue and the torque converter looks like a newer replacement one, i at least know it has been out and some work has been done to it for sure, but i dont know what exactly, it wasnt painted in the truck cuz there is no blue overspray on anything anywhere at all,


i would really would appreciate anything on this,

thanks for your time and info

 

There should be some line pressure ports on the tranny but expect to have to pull the tranny for inspection or repair.

 

line pressure ports

i think theres only one on the th350

what is line pressure exactly ?

how can i learn anything about the trns by using it ?

how do i use it ?

thnaks

 

Once you locate the ports you can find yourself a trans shop manual that will give certain PSI readings that the trans needs in each gear to function properly. Know what kinds of pressure your trans puts out will help you go a general direction with what may be wrong.

 

theres only one pressure port on a th350 right ?

what kind of tester do you need ?

how do you test the pressure for 3rd gear only ?


if you cant then theres no point here

does anyone not know anything specific here?

if not then where should i be asking ?

we have no shops here for trannies, not a single one

the last guy who did them locally closed shop and left town, i got to haul away all the parts and trannies he had- all 4,440lbs of it to the shredder
i probably should have kept the goodies, hum, but i dont know much about trannies, i wouldnt have known one part from another, and i still really dont, other than i know what the clusthc discs are and the torque converter and such lol




thanks

 

That's the single most common TH350 failure.

Direct clutch lip seal.

Time for a rebuild. Nothing you can do from outside the case.

 

Actually the most common failure in a TH350 is the intermediate sprag exploding.

 

Iunno bout that...

I've probably had a half-dozen of them fail by 3rd gear going out; haven't had even one yet die from the sprag.

We're not all track junkies, you know. The seal is how they die on the street.

 

The stock apply circuit for 3rd gear only in TH350's & TH400's uses only the inner half of the apply piston. Installing a TransGo Performance Shift kit will use the inner & outer half of the apply piston. If the clutches are still in somewhat good shape, this can fix it till you go through the unit. When TH400's start to do this the installation of the TransGo Performance Shift kit can solve this too.