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Discussion Starter #1 (Edited)
i 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
 

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There is quite a bit of load in 3rd gear on the 3rd clutches because of the lack of gear reduction (direct drum). There is even greater load in reverse because of the gear multiplication effect.

So 3rd gear will be the first gear to fail in a TH350, usually causing reverse to quit working also.

My guess is that you have a lip seal on the direct drum (3rd gear) that is cracked or hardened and it is bleeding pressure off the directs causing it to slip.
Bad news is, it likely needs a rebuild.

There is one thing that may let it work for awhile by cheating a bit.
If you install a valve body kit such as a TransGo Reprogramming kit or even ( I rarely suggest this) a B&M shift improver kit, it will dual feed the clutches. You'll be using the reverse portion of the direct apply piston in addition to the direct (3rd) portion.
If you do use the B&M kit, do NOT drill the holes to the huge sizes and leave out all the checkballs that are instructed. Re-install all the checkballs and don't drill the plate (excessively) or leave out the 1-2 accumulator spring.
It may be worth a try for $30.
 

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Discussion Starter #3 (Edited)
im VERY willing ot gamble away 30 bucks lol

can i do this without pulling the tranny ?

i really do not want ot have to remove the tranny, because the NP203 case bolted to the end of the tranny is freaking HEAVY

sounds like i need to get one of these kits and cross my fingers

i have never installed one of these in a trans and have no idea whatsoever what to do, i have taken apart a few th350 trannies before but i cant do much more than that to one, i have never done anything serious to one, but if you give me an engine well i can tear it down and rebuild it totally no problem at all, so..

trannies are just so wierd.....

hmm..

thanks for any further info/suggestions !
 

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Pulling a TH350/NP203 in combination isnt nearly as scary as it looks.

Yes it is very, very heavy. With a GOOD floor jack it can be removed, no need for a fancy transmission jack.

Round up a good buddy or two and you can have it done in a few hours. It certainly wont take all afternoon.

Hopefully youll get by without having to pull it.
 

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Discussion Starter #6 (Edited)
ive pulled transmission/TC combos before but never without pulling the body off first and using an engine host to lift the combo off the chassis,

dont have concrete or anything out here so the floor jack method is a no-go

so thats why i am hoping that a kit will fix it, or fix it good enough at least for a long while


any details on installing one of these kits and reccomendation on which and from where to get it would be great

there summit and FWP and napa and all kinds of places, and many different brands of the kits and even different ones

what to get ?? the b&m or the transgo or ?
i cant find the transgo one anywhere, is it really called a shift kit ??

heres the b&m ones on summit
http://store.summitracing.com/egnsearch.asp?N=700+115+300206&D=300206


but at summit it says theres two different B&M ones, strip, and towing ?? i take it that i would want the towing one right ??

i cant find any results for a transgo shift improver search
does it exist anymore ?



which kit will most likely cover what i need to accomplish with this transmission and its symptom/issue ? which do you recommend more ??


its in a stock 4x4 daily driver truck, so..,.


thanks!
 

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Discussion Starter #7
check this thread out http://www.doityourself.com/stry/warmweathershiftproblem

that guy has the EXACt same issue with this truck th350

i have good working order reverse BTW

should i try another governer and another mod valve first ?


wheres this valve spring he is talking about ? could it really be that too ?

should i drop and disassemble and clean the VB or swap another one on ?

i have another th350 trans identical to this one out here that is supposed to be good but its really dirty i could use for parts



thanks
!
 

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For this deal, just get the B&M shift improver kit at a local parts store. Most stores carry them if they carry any aftermarket stuff. Pep Boys, Shucks, O'reillys, Napa, etc.
It has two possible ways to set it up. towing and "street/strip". The street strip method as instructed is one of the best ways to cause harm to a TH350 IMO, but install the kit using the towing mode. However don't drill any holes, and reinstall all the checkballs. Also do not remove the 1-2 accumulator spring. What this will accomplish is dual feeding the directs via the small plate that is sandwiched between the support plate and case. This is all you are really trying to do.
 

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Discussion Starter #9
awesome!

thanks! :D

i guess thats all i need to know then, yay :D


thanks everyone :D :thumbup:
 

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Discussion Starter #10 (Edited)
ok i have a couple new questions,

whats the good book to get for rebuilding one of these th350 trannies

and, i have a good working 1981 th350-C 2wd trans from an 81 c-10 pickup with 350 diesel dual bolt pattern

i think i want to swap the 4x4 output shaft into it and do a basic rebuild on it real quick -after i find a stock gas engine converter for it since it had a diesel one that i scrapped

if there was a way to convert it to the non locckup parts then i would- but im told the cases are different ??
what about the VB ?
not possible to convert it to non lockup at all right ?



thanks
 

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I have this book and can highly recommend it. Very comprehensive.

I also have a video that is pretty good, but I don't have the contact information here at the office. It was produced by a guy named Wayne in Wichita, stars a guy named "Flip." Shows a complete tear-down and hi-performance rebuild of a TH350. I'll post a link when I get home tonight.
 
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