TH 350 Issues

[BigAl285]

I'm a newby here, I like the site been here many times just never posted. I have a 75 GMC 4x4 33'' tires, 383 stroker putting out 500 hp and a 2500 stall. I have a TH350 trans. I'm setting it up for truck pulling. My truck came with a TH350 trans and I thought I'd give it a try with the whole deal with the rotating mass robbing horsepower on a s.b.c. It would slip inbetween 2-3 gears. I bought a TCI rebuild kit for my trans. I disassembled it but then needed a couple special tools. I took it to a guy who has "30" years of experence. Well transmission will be pulled for the third time. You can't tell when it shifts, no power what so ever. I can't remember the exactly what the guy also replaced beside the rebuild kit I wanna say modulator valve, boost regulator, Transpro shift kit (had one in it before) and a couple other things that I dont remember. He pulled the trans apart says everything is correct. The torque converter isn't being pulled out of the oil pump. Vaccum line are free flowing, no kinks in it. Fluid is at the full mark. Didn't get trans to operating temp because its not correct. Torque converter bad ( brand new too), Any other ideas?

 

[swagger]

Whats the 30yr trany guy say about this??
Steve

 

[BigAl285]

He has 30 years experence forgot to add that. Torque converter he says

 

[crazy4offroad]

Since you're pushing the envelope of the 600HP rating of the stock intermediate sprag race you may want to make sure he put a hardened one in...
http://www.transmissionpartsusa.com/TH350_transmission_parts_p/470-000047774.htm

You may want to read this how-to on building a TH350 for higher performance, some of the tips and tricks in it are interesting...
http://www.hotrodders.com/forum/th350-rebuild-tech-145361.html

If the slip is only between 2nd and 3rd I have my doubts it is the torque converter. I would be checking the direct & forward drum's apply pistons and seals for cracks/tears that could cause pressure loss, or too much clearance of the clutch packs. You could also have an actuator hanging in it's bore in the valve body. Then again it could be something REALLY simple, HotRodPC or oneluckypops would be the guys to ask, maybe shoot them a private message.

 

[BigAl285]

My trans slipped between 2-3 before the rebuild. Went back to where I got the stall torque converter. They took it back and I got a new one. Drove it tonight on the road and it worked finally. I guess I had a bad one. Thanks for the tips too!

 

[crazy4offroad]

Good to know, thanks for posting back the cure!

 

[swagger]

That sprag will go next if its not a good one, it has to stop that drum for the next gear change.
400's I build I use the 34 el sprag VS the 16
It will junk that tranny if it comes apart
Be easy on her
Steve

 

[BigAl285]

Thanks! I have the sprag done like you said. He said I have a very good trans. Its from the early 60's. We will see how good it is now after all the work thats been put into it haha.

 

[HotRodPC]

So the issue was the Torque Converter??? That would have had me stumped too.

Doubtful it's from the early 60's. Th350 started in 69 to replace the Powerglides going from a 2 speed auto to a 3 speed auto. Th400 started in the mid 60's.

 

[BigAl285]

Yup it was the torque converter. I dropped down to a max stall of 2500 my larger tires didn't help also. Ok well I'll say my trans is from the whoknows when Haha

 

[HotRodPC]

It doesn't really matter what Th350 you get. Pro's and Con's to both. The best ones are the ones that from the older days, and put together with the later newest guts IMO, but really they are pretty much same in strength all the way up until you go to the lock-up converter model then you get weaker in the input shaft and the converter itself.
Th400's do matter. You want old as possible for the good sprags, but the newer ones have things like case saver rings, more bearings in the Torrington bearings etc, so mixing the old with the new is a good thing on Th400's.