Re: Bulletproof TH350 ?
 

400's break intermediate sprags too.

Re: Bulletproof TH350 ?
 

So, these mods you describe are almost an AAMCO rebuild, huh ? :D

Re: Bulletproof TH350 ?
 

Yeah, my 1st 455 proved that to me. After it broke the 1st one, I ask around and somebody told me to ask a local tranny guy who had built lots of TH400's for the local racers. When I described to him what had happened, he said, yeah, it broke the int sprag.

Well hey, I was just starting out. I'd never even heard of an int sprag. He said all I needed was a GM sprag for a TH400 that came behind a 500 Caddy engine. So he put one in for me and I never had any more trouble out of that tranny.

Then I bought a TCI "Full Competition" TH400 with a reverse pattern VB, for another car. But my 455 broke it too. When it broke, the guy who was driving the car came back from a time trial and said he didn't have any 2nd gear. So I told him to just hit the ratchet shifter twice real quick and see if it would shift from 1st to 3rd.

He did and it did. It only ran a couple of tenths slower. It was a bracket race. So we just dialed in to the slower time and he won the race. :D

I ask the tranny guy about it and he said that just because TCI called it "full competition" did not mean they had put the HD sprag in it. He was right. He put one in it and I never had any more trouble with it.

I suspect that TCI changed their tactics a bit since those days. Anyhow, I think several of the tranny shops use to buy the Caddy sprags and repackage 'em. In recent years, they are probably made in China. I see the 34 element sprags on Ebay for anywhere from about $50 to almost $100.

http://www.ebay.com/sch/i.html?_odkw...&_sacat=171114

Re: Bulletproof TH350 ?
 

I have a friend with an 8 second (if he feels like it) SS car using a Pro Trans T350, never an issue. He put me onto them. The Smith family has been very good to deal with.
I understand A1 buy parts from them and builds the same thing?

Re: Bulletproof TH350 ?
 

Another thing that kills the 2nd gear sprag these
guys that drill the separator plate out for 1-2 shift
so big that your teeth actually hurt when it shifted.

Re: Bulletproof TH350 ?
 

X2. A friend of mine had a Trans Am years ago with a TH-350 that had a "big name" shift kit in it. The trans shifted so hard into 2nd that you would think it was going to crack the windshield, yet he liked it. The car had T-tops and I think that exaggerated it as well.

Also, if the intermediate accumulator spring is broken or has been removed, it will cause a violent shift into 2nd as well.

Re: Bulletproof TH350 ?
 

I think there may be some confusion with the term sprag. By definition a sprag is a mechanical one way clutch that can be many different configurations. The Turbo 400 built by Hydra Matic used a Borg Warner sprag assy. from 1964-1971. After 1971 it was used only in high performance applications and was replaced by a one way clutch called a roller clutch. Both are adequate for stock applications but the Borg Warner sprag is MUCH more robust.
The Turbo 350 built by Chevrolet and later by Chevrolet and Buick was only built with a roller clutch.
The roller clutch which is much cheaper to produce uses a series of rollers, springs and a cam race. By design the outer race in put in tension and the inner race in compression when force is applied. That said there is an amount of force that will break the outer race at the lube holes. Both the 350 and 400 can easily be converted to the Borg Warner sprag which is a one way clutch comprised of a smooth inner and outer race and a series of segments that wedge to hold one way and freewheel the other. The 400 can be converted using ALL production parts. The 350 requires an after market drum with a modified inner race.
One last thought ALL 4L80E transmissions use the Borg Warner 34 element intermediate sprag assy. which interchanges with the 400.

Re: Bulletproof TH350 ?
 

Yeah, there are usually several of these later parts to convert the 72-up TH400's to the 34 element sprag, for sale on Ebay.

http://www.ebay.com/sch/i.html?_odkw...&_sacat=171114

There are several brands of 36 element sprag / drum / race units available for the TH350. Here's some on Ebay, including one that says it has a "mechanical diode" instead of a sprag or roller clutch. Anybody using this kind, or have any info about 'em ? :confused:

http://www.ebay.com/sch/i.html?_odkw...&_sacat=171114

Re: Bulletproof TH350 ?
 

Oldskool, The drum offered with the mechanical diode is a part from a Ford 4R70w modified to fit the 350 drum. The mechanical diode is a ratcheting one way clutch designed by a company called Epilogics. It is used in many production units and is sometimes used in torque converter stators.

Re: Bulletproof TH350 ?
 

This is a great thread for info I will need. I will be running a 396-325 HP combo in my 65 Impala I am building now. This is the same same motor out of my 68 Impala I raced 10 years ago but with a Jerico. I never ran the motor on a Dyno but using those HP Caculators shows 500 HP at flywheel but no torque figures. I will be using a TH350 that I bought back in 2002 for $800 . I know it has a manual valve body plus the the lower 1st gear upgrade (2.76?) but besides that don't know much about it. It has been sitting since then never used. Sounds like I should check for that roller clutch and just upgrade for the drum/sprag and be done with it. This is not a "dime rocket" but you know... If i still had the Jerico and clutch. damn.

Will Lamprecht I/S 65 Impala in progress (on build page)