TH350 stuck in high gear!

HotRodGMC68 · 11-09-2009, 03:06 PM

I recently got a used TCI Competition TH350 from a buddy of mine. When he last used it real hard he hot lapped it 5 times and got it super hot. After that it was stuck in high gear.. he called TCI and they swore up and down that it's in the valve body. OK.. he had the valve body rebuilt at a local trans shop with a good rep for high performance parts. It worked great afterwards just cruisin' around the streets of town.. once he got on it real hard ONE time it was stuck in high gear again! He yanked it out and replaced it with a 400.

I aquiered the 350 and put a brand new TCI manual, fwd. pattern valve body in it... identical to what came out of it. Now the tranny is stuck in high gear wheather it's hot or cold! I do have reverse and neuteral.

Are there any tranny guru's out there that can lent some advice or knowledge on this thing?? I'd greatly appreciate it! I have torn down, inspected, and reassembled both valve bodies and they were both cherry from the get-go.

I haven't had time to tear it down the rest of they way, with having a 15 month old daughter taking up my free time..

Thanks a bunch..
Kurt S.

Tom Goldman · 11-10-2009, 07:50 AM

Pull the valve body down and check the case with a straight edge to make sure the case is flat. ....any distortion can cause leakage across the channels. ..............It is more likely that you have a pump issue , since the problem has ocoured with two different valve bodies......internal leakage in the pump from the foward clutch passage to the direct passage will give you high gear. .....Reverse will function normally because the foward clutches are turned off and the direct clutch is applied. ........I'd find someone who is familiar with performance 350's and have them take a look at it,and spend the time with your kid!.....Tom

buzzinhalfdozen · 11-10-2009, 09:07 AM

I agree you must have an unintended pressure leak, 2 most likely spots are the Valve body area or the frt. pump gasket area. A full manual valve body would not cause this issue unless there were a crack or porosity, since you've changed it you can rule that out. I would do as Tom suggested and have someone familiar with these trans. look at it, may save you money in the long run. Joe

HotRodGMC68 · 11-10-2009, 10:40 AM

Thanks a bunch guys! The first chance I get I'll dig into it and find out what's going on! And don't worry Tom.. I plan on spending as much time with my little girl as I can!

11-09-2009, 03:06 PM	#1
HotRodGMC68 Junior Member Join Date: Oct 2009 Posts: 7 Likes: 0 Liked 0 Times in 0 Posts	TH350 stuck in high gear! I recently got a used TCI Competition TH350 from a buddy of mine. When he last used it real hard he hot lapped it 5 times and got it super hot. After that it was stuck in high gear.. he called TCI and they swore up and down that it's in the valve body. OK.. he had the valve body rebuilt at a local trans shop with a good rep for high performance parts. It worked great afterwards just cruisin' around the streets of town.. once he got on it real hard ONE time it was stuck in high gear again! He yanked it out and replaced it with a 400. I aquiered the 350 and put a brand new TCI manual, fwd. pattern valve body in it... identical to what came out of it. Now the tranny is stuck in high gear wheather it's hot or cold! I do have reverse and neuteral. Are there any tranny guru's out there that can lent some advice or knowledge on this thing?? I'd greatly appreciate it! I have torn down, inspected, and reassembled both valve bodies and they were both cherry from the get-go. I haven't had time to tear it down the rest of they way, with having a 15 month old daughter taking up my free time.. Thanks a bunch.. Kurt S.

11-10-2009, 07:50 AM	#2
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,473 Likes: 878 Liked 857 Times in 234 Posts	Re: TH350 stuck in high gear! Pull the valve body down and check the case with a straight edge to make sure the case is flat. ....any distortion can cause leakage across the channels. ..............It is more likely that you have a pump issue , since the problem has ocoured with two different valve bodies......internal leakage in the pump from the foward clutch passage to the direct passage will give you high gear. .....Reverse will function normally because the foward clutches are turned off and the direct clutch is applied. ........I'd find someone who is familiar with performance 350's and have them take a look at it,and spend the time with your kid!.....Tom __________________ Tom Goldman 1500 SG , 1506 STK

11-10-2009, 09:07 AM	#3
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: TH350 stuck in high gear! I agree you must have an unintended pressure leak, 2 most likely spots are the Valve body area or the frt. pump gasket area. A full manual valve body would not cause this issue unless there were a crack or porosity, since you've changed it you can rule that out. I would do as Tom suggested and have someone familiar with these trans. look at it, may save you money in the long run. Joe __________________ Joe Buchanan SS/BX 3117

11-10-2009, 10:40 AM	#4
HotRodGMC68 Junior Member Join Date: Oct 2009 Posts: 7 Likes: 0 Liked 0 Times in 0 Posts	Re: TH350 stuck in high gear! Thanks a bunch guys! The first chance I get I'll dig into it and find out what's going on! And don't worry Tom.. I plan on spending as much time with my little girl as I can!