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Old 10-28-2007, 07:35 PM
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Stock TH350 capacity

Hey crew,

What will a stock TH350 handle for HP and torque?

I've picked up a low mileage roller block out of a '97 silverado and I also got a set of ported vortec heads for it. I'm planning on a cam swap, some roller-tipped rockers, and between 350-375 streetable horse for my 71 Chevelle that originally came with a 307. Currently has 38,000 on the drivetrain.

How well will the stock TH350 hold up to this? I'm not going to pound the crap out of it, just more of daily driver-type duty. Can I get by with a big tranny cooler and a RV-level shift kit, or will I fry this tranny in no time?

I already spent my fun money for awhile on my motor, so cost is really an issue. I also do have a spare TH350 on the garage floor that worked good oh, about 10 years ago when I yanked it out of a G-body that had a 350 in it, so I could get that rebuilt and still drive my Malibu. Just something to consider.

I talked to a guy at a tranny shop in town last week--one with a real good reputation--and he claimed he'd need $900 to build a TH350. The price for the TH350, mind you, was for a complete performance run through, not just a rebuild. New sprags and all that stuff. He said between $250-$400 for just a stock or HD rebuild, depending on what I want. Does this sound like a reasonable ballpark? Seems like you can get a brand new one for $900 from Summit or TCI or B&M!

Thanks!

Last edited by 307malibu; 10-28-2007 at 07:36 PM. Reason: wording error
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Old 10-28-2007, 08:17 PM
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Well, think of it like this. An engine only makes the amount of torque that it has to to achieve what you want it to at that given time.

So, if you drove it easy you could run a 460 through a motorcycle transmission.

Pretty much what I'm saying is for a daily driver that occaisonally gets a romp on it, a stock low mile TH350 with a shift kit will hold it as you save you money for when it goes out. If you intend on beating on it the way it's meant to be beat on, a real build should be in order before it hits the street.

Justin
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Old 10-29-2007, 04:58 PM
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Stock?

3oh7, it all depends on what you are considering stock. If the tranny is completely stock, ie. no shift kit, it won't hold up to a strong 350 very long.These trannys are built with a lot of "cushion" for granny shifts. The best thing to do is pony up for a Trans-Go 350 1&2 shift kit and install that before you start getting the urge to romp on it . Go ahead and pull the accumulator spring out of the intermediate accumulator located on the passenger side of the tranny. These springs are prone to breakage and if one ever breaks you can just about say good bye to the acc. piston bore in the housing.

I don't get that much to build a threefiddy, but I have noticed a lot of shops are charging up to $900 to build one. That is way too high in my opinion, but if you don't know how to do the work , you're gonna have to pay someone to do it. A good heavy duty build with the hardened intermediate sprag race and the TG 1&2 Shift kit will easily handle your 350. No need for the $900 "full race" version. The intermediate sprag race will run between $30-40, the shift kit less than $50. I take it, that for the $400 HD build he will replace all the bushings and thrust washers and set the clutch pack clearances and end play properly. End play is critical in these trannies if you want it to live. These will last if you take the time to build it right.
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Old 10-30-2007, 10:24 AM
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accumulator spring?

Thanks for the info., 70 elcam. Looks like I'll find another shop before I go dropping $900 on it.

I'm not experienced much with transmissions, but I did install a governor recalibration kit in the TH350 I'm running now. I do have a B&M shift kit--so I'm thinking that the shift kit, a nice cooler, a deeper aluminum pan, and removing the accumulator spring will get it done for everyday use? What will the removal of the accumulator spring do to the performance or behavior of the transmission? Also, would you go with the "RV" level on the shift kit? I don't want it to be too uncomfortable with the wife along!

Thanks for your help!
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Old 10-30-2007, 06:16 PM
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Quote:
Originally Posted by 307malibu
Thanks for the info., 70 elcam. Looks like I'll find another shop before I go dropping $900 on it.

I'm not experienced much with transmissions, but I did install a governor recalibration kit in the TH350 I'm running now. I do have a B&M shift kit--so I'm thinking that the shift kit, a nice cooler, a deeper aluminum pan, and removing the accumulator spring will get it done for everyday use? What will the removal of the accumulator spring do to the performance or behavior of the transmission? Also, would you go with the "RV" level on the shift kit? I don't want it to be too uncomfortable with the wife along!

Thanks for your help!
307, the acc. spring is a cushion for the shift into the intermediate range(2nd gear to us gear bangers). Removing it will stiffen up the shift somewhat. With the B&M kit set to RV specs it won't be too harsh for everyday driving. I've seen a ton of these broken over the years, with the worst case scenario a gouged up acc. bore. I take them out of all my 350s.
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Old 10-31-2007, 01:31 PM
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spring location

Ok elcam, you're giving me a ton of help here, so thanks. Now, I take it that the round cover on the passenger side is removed and then the accumulator spring just pops out? Doesn't sound too hard to do.

Speaking of, how hard is it for the average guy to replace clutches and the intermediate sprag race? I see B&M or TCI kits for less than $200 in catalogs and they apparently come with a good manual--good idea for a first timer or no? I've got to learn somehow, right? Or is it better to just pay someone else in this case?

Thanks!
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Old 10-31-2007, 10:36 PM
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Actually, I"ve never bought one of those kits that you mention, so I don't know whether they have a manual in them or not. If you are good with taking instructions through reading, I suggest buying a book by HP Books titled Turbo Hydra-Matic 350 Handbook, written by Ron Sessions. I bought it over 20 years ago and it has some very useful info in it. Well illustrated. Gil Younger at Trans-Go has taught me a whole wealth of transmission tech since I started at age 16. I'm not a trans tech, I just do this as a hobby at times. I'm building one now for a rock crawler buddy of mine. It's gonna be fun.

On the acc. cover, use a sharp awl or small punch( a nail will work) through the hole in the rear of the acc. bore to lift the C clip out of the groove enough to get a small flat blade screwdriver under it to pop it out.Then use some channel locks to wiggle the cover out of the bore. It will need to be rocked a bit to get it out. If you have the VB off, you can used compressed air to pop the piston and cover out of the bore, but be careful doing it that way. Now, when you go back in with the acc. cover, install the new "lightly greased" o-ring into the bore first , then push the cover into the bore as far as it will go. Install the c clip into the groove . You have to be careful that the cover goes in straight or the o-ring won't seal and you'll have a big mess on your hands when it shifts to 2nd. Then you'll have to do it all over again, under the car, not fun. Good luck with your tranny.
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Old 11-01-2007, 10:16 AM
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Thanks, elcam. I'll start from there and see how it goes!

Appreciate your help.
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