Bulletproof TH350 ?

[Jim Kaekel]

Originally Posted by bigfoot584

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.

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.

[Lou Jeffery]

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.

[oldskool]

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 ?

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

[Lou Jeffery]

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.

[impstocker]

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)

[rallye bob]

The EMC (engine masters challenge) is getting a little out of control, and boring ... I love the carb challenge, but now, I'm up for a TMC (transmission masters challenge)...... Next up........ RDC (rear differential challenge)... ;-)

[Dean Feiock]

As for TH350, not all 36 element drums are created equal. I would suggest you look for the following items when searching for a drum.

A) While the Ford / diode conversion may be strong, it's very heavy. If you're looking for strength it's ok. For strength and ET savings, not so good.

B) A good drum will have a new inner race installed, not a reground original.

C) The inner race will be pinned in 4 places to keep it from rotating. If the race is just held from rotating by using the factory 2 or 4 half moon lugs, it will work away until it breaks.

D) The best outer race is one with made from new steel and NO oil holes. Stay away from re-heat treated off shore stuff.

Poor accumulator set up, valve body design, and cushion springs won't break intermediate sprags and races. But rather poor sprags and races break. If you have to baby it or cushion it up, you are not using good parts. Put good parts in it and forget about it.