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Old 06-04-2009, 07:47 PM
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Building a TH350C from scratch

I had a "reputible" local shop build me a TH350C from scratch and they cannot get it to work.

The lockup does not work. They replace the solenoid and still nothing. I'm assuming they made sure voltage was getting from my switch to the solenoid. I know it has plenty of voltage at the connector.

The torque converter is a fresh build.

I'm a little concerned b/c when I talked to the girl at the desk on the phone today she said they still weren't able to get it to lock up. She said something like, Maybe it won't work for your application. I know that's a load of crap. It's a 4x4 Chevy Blazer. I think they're just getting tired of messing with it.

What could this guy be missing or not doing right?

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Last edited by 70bird; 06-04-2009 at 09:34 PM.
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Old 06-04-2009, 08:43 PM
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Lockup

Perhaps they didn't put the oring on the end of the shaft that seals the oil that locks up the clutch in the converter? Is it a Dayco remanufactured converter? I have had a few runs of bad luck with them. The valve body may still have a problem they haven't figured out yet, or one of the seal rings were cut during assembly? Good luck!
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Old 06-04-2009, 09:00 PM
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The first mistake was using the "C" variant in the first place, they barely worked well in a stock application and are definately not worth the hassle. Why the 350C?
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Old 06-04-2009, 09:31 PM
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He has a local guy build the converters.

Thanks for the info. I'm compiling a list of questions and going down there tomorrow morning.

Hopefully this guy stays cool and is willing to work it out. Otherwise I'm going to have to damand a full refund for not being able to build the transmission correctly and I'll bring my old trans in and have him reinstall it. Or I'll swap it out and take it back.
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Old 06-04-2009, 09:33 PM
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Quote:
Originally Posted by ericnova72
The first mistake was using the "C" variant in the first place, they barely worked well in a stock application and are definately not worth the hassle. Why the 350C?
Hoping for a little better fuel economy on the freeway.
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Old 06-17-2009, 07:18 PM
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Following up...

The reason the lockup wasn't working was due to the performance mods made to beef up a typical TH350.

The mod that increases holding power to third gear on a typical TH350 (something about tying into the reverse circuit which adds pressure to the drum) conflicts with the lockup circuit. The lockup circuit also uses the reverse circuit. The 3rd gear mod made it so that the lockup solenoid could not actuate.

A vent hole needed to be drilled (don't ask me where) to allow the lockup solenoid to actuate.

Just be sure not to increase a certain hole size too much (from .019 to .03). This will cause the converter to lockup (w/out lockup solenoid being powered) when the trans is placed into reverse or in third gear.

Keep in mind... I'm not a tranny expert...I'm just relaying how it was explained to me. Feel free to correct or clarify any info I may not have been completely accurate on.

My trans guy said he now knows more about TH350C's than he ever wanted to know.
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Old 06-17-2009, 07:41 PM
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Quote:
Originally Posted by 70bird
My trans guy said he now knows more about TH350C's than he ever wanted to know.
lol- that's kinda funny.

From what I can tell, it seems that the closer you get to making the "C" variant into a non-"C", the better.

Which leads me to believe that starting w/a "C" isn't the hot ticket. Shame, that's what I have in one of my projects- '80 Malibu w/229 V6, soon to be a V8, prob. another belly-button 383.

Someone was here a while ago, said he had gotten one built to stand up to "regular" TH350 levels. Never heard what was actually done, or if he had actually USED it or not.
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Old 06-17-2009, 08:01 PM
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You can do all the same mods to a TH350C as you would to beef up a typical TH350. The problem is, when you do these mods the lockup feature will no longer work.

If you want the lockup to actually work, you'll have to do some additional mods to the valve body.

The guy that built the trans said he built it to hold up to my BBC (~500 lb ft of torque turning 35" mud tires and 4.10 gears). He always has at least one hot rod on a rack in his shop. That's usually a good sign.

Last edited by 70bird; 06-17-2009 at 08:34 PM.
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Old 06-18-2009, 08:14 AM
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There's nothing wrong with the C variant of TH350, it can be built very strong and it's not inherently weaker than any other TH350.
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Old 06-19-2009, 05:58 PM
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i completely agree with jake

i have one and it actually looks feels stronger than a non C one, as far as the case thickness and design goes

dont know on internals

im keeping it

plus i like that its a 10 bolt bellhousing to fit all gm division engines 90 degree pattern

like the 2004r are

most ppl that dont like these dont because they are not "mainstream"


good luck
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