considering swap out my th350 trans and install th400
 

i have a 78 Trans Am numbers matching survivor car. original paint, original interior etc.. in really nice condition with 70,000 miles. i recently pulled original engine and have it in storage to maintain the original engine. i now have a 72 400 block with stroker kit from butler 461 now.. has 6x-8 heads milled for a smaller combustion chamber.( 96 cc) flatop Pistons. roughly 9.3 to 1 compression. Comp Cams XE274. Comp Cams Roller tip Rockers 1.65 ratio.. R.A.R.E. exhaust manifolds. 2 1/2 inch collector. full PYPES 2 1/2 exhaust with Violator mufflers. has a semi rebuilt q-jet which will need more tuning.. has a th350 now which is leaking a bit. current rear is 2.56 and planning on 3.08 soon. also currently have a 2200-2400 stall. my thought are if i pull the th350 to at least regasket it i might as well rebuild it.. and if gonna rebuild it im thinking th400.. so i can preserve original th350.. thoughts?? and if i do the swap what can i expect as far as problems.. what needs to bedone to make the swap.. thanks as always for the info.

If you go TH400 you will need different drive shaft, different crossmember, find some way to utilize the TH400 electric kickdown deal.
Yes TH400 is stouter but may not be needed in your case.
Improvements can be made your th350 during a rebuild. I'd stay with the th350.
If you had a serious 500 plus HP, it would be different.

I also recommend staying with a TH350. But, with the torque of your new engine, I'd go with a heavy duty build, using the 36 element sprag/drum/race upgrade.

http://www.coanracing.com/Catalog.as...uctDetail=1573

http://www.jakesperformance.com/th350/

I will echo mr trashcans thoughts. Sticking with the th350 would be the most cost effective and least amount of labor. My friend and I have been going back and forth on this same issue on his 77. One thing were not sure of is parking brake cables might also be different as (mentioned) the drive shaft length and cross member too... If you really want to save the numbers matching trans, just get another one and build that one. Also, think the 3.08 is good gear for all around compromise. Were considering a little more gear as we don't do any highway driving. Just some thoughts as our build isn't exactly like yours.

ok great info.. i was also considering get another to keep original in storage.. ok i feel a bit better about the th350 rebuilding one to a heavy duty build.. didnt think there was that much involved to swap to the th400.. and agree i think the 3.08 is good.. i did purchase a 3.42 first and decided its gonna be too much gear for what i want to use it for.. which is alot of street driving and some highway crusing.. more so then track time. so i also purchased the 3.08. that will go in over the winter. along with the transmission swap..

actually looking on craigslist and just found what looks to be a good rebuildable core for $50.. i think thats the route to go.. i most likley will looking for advise on a master rebuild kit.. and what other little goodies i might need to beef it up.

Nobody wants th 350's or th400's anymore. Everyone has to have an overdrive.
Big torque Pontiac's can handle the high rear end gears. Not so, in Chevyworld.

LOL.. this is true.. i almost was thinking to go over drive route.. but i think would be way too much effort and cost.. with not much benefit..

Another vote to stick with the 350 trans and just build it up a bit. Not worth all the hassle to swap to a 400 in this case. Been there, done that with a 76 Formula. Ended up switching back to a 350 later on anyway.

great.. thanks for input... the 400 eats a bit more horsepower also right?? heavier mass to spin..

The TH 350 in my 78 has spent lots of times in high 10s and low 11s.

Years ago my engine builder told me 10-12 hp more needed to turn a th400 vs a th350.

Skip, what modifications have you performed on your th350?

I've never had anything resembling a powerful engine in my car, but I installed a B and M transpack at about 20,000 miles. I wonder if that has helped it's life expectancy. My trans has about 120,000 on it, it's never been out of the car. Wish I could say that about the engine (number 7 each lobe started go flat around 75,000).

You know I do not know all of them. It was built by Phoenix for one of my local Buick buddies that ran NMCA with me to Jim Turner's specs. Jim ran a Stage 2 GS in the the old classes we ran.Not sure if it got the better 32 element parts in it or not. heck I ran a bone stock rebuilt one in the low 12s for a lot of years before my first E head motor tore up a Trans King convertor in it after I put my first 455 E head motor in it. The Phoenix tranny and a 5000 stall A-1 dropped the car 0.75 seconds!

One I just had built for the 409 project has all the good stuff and was close to $2K.

There's a time and place for a 400. I'm just not a fan of them in my cars and even dumped the one in my 70 GTO many years ago.

The 350 is a great trans for many reasons, especially in 75-81 F cars. If I were to ever go back to a 3 speed trans for some reason, it'd still be a 350.

If you are not already a TH350 rebuild expert, you might wanna acquire some written help. Cliff has a TH350 Book. There are others, and I'm sure there is lots of online help.

https://www.amazon.com/GM-Turbo-350-.../dp/1613251890

There are several sources for the 36 element sprag/drum/race assembly. I think the TCI 327900 assembly is the cheapest. Not sure which brand is the best quality.

https://www.tsr-racing.com/th350-dru...ent-sprag.html

https://autoplicity.com/394905-tci-a...xoCTYgQAvD_BwE

https://www.amazon.com/TCI-327900-St.../dp/B000NZYNC8

http://www.coanracing.com//Catalog.a...uctDetail=2276

https://www.summitracing.com/parts/a...hoCVt0QAvD_BwE

https://transmissioncenter.net/shop/...mediate-sprag/

http://www.jegs.com/i/J-W-Performanc...RoCeZUQAvD_BwE

This set-up claims to be better than the 36 element sprag deal. I can't verify.

http://www.ckperformance.com/View/SU...CHANICAL-DIODE

I think most agree that Trans-Go is the best brand for a shift kit.

https://www.summitracing.com/parts/t...BoCv0UQAvD_BwE

http://www.ebay.com/itm/TransGo-TH-3...38.m2548.l4275

Here's a popular rebuild kit.

http://www.altousa.com/am/high_performance

http://www.ebay.com/itm/TH350-TH350C...26.m2548.l4275

https://www.amazon.com/TH350-Eagle-K.../dp/B00ZB6CN5I

http://dragtrans.com/dragtrans_html/HPOHK.html

this is awesome info..!!!! thank you..

i have rebuild engines.. but only minimal trans work.. and was planning on cliff's book.. also a good friend who has rebuilt transmissions before is on the hook and lives like 1 mile from my house. sent message to the guy with the th350 local that i found on CL.. for $50.. that would be perfect.. and close by.. like 15 minutes away..

Make sure your actually buying a bop 350. Can't tell you how many people brought me cores to build that were later lock up units, or Chevy bell. 2 weeks ago a guy brought me a metric 200 he was told was a 350 from craigslist, I told and showed him what to look for and he brings another 200.

That's actually funny!:D

But if he wants to unload one or both of the 200's, PM me.

If you have enough bottom end grunt, you can run a taller rear gear and still use the 3 speed.

There may be some ET loss due to the greater weight of the 400. But I don't believe there could be a significant internal power loss between the two. Everything is locked in hi gear on both.

A bit cleaner look under the hood without the 350 TV cable.

" Make sure your actually buying a bop 350..."

You can use a Chevy TH350. Just takes a simple adapter plate. You can buy one or make one. I made one and used it with a PG & a TH350. My 455 broke both trans, but the plate worked great.

http://www.jegs.com/i/JEGS-Performan...60172/10002/-1

Or, if you really wanna build a heavy duty TH350, you can replace the bell with a JW Ultra Bell.

https://www.summitracing.com/parts/j...xoCmE4QAvD_BwE

http://www.jegs.com/i/J-W-Performanc...BoC-pAQAvD_BwE


"...A bit cleaner look under the hood without the 350 TV cable."

Can build to run without the cable. Lots of rebuilt performance TH350's come without the cable. I've read lots of back & forth about whether the kickdown cable controls line pressure, or is only for shifting to a lower gear, when you floor the pedal. I'll leave that discussion/argument for others. Some have reported great operation, for many years, without the cable.

http://nastyz28.com/threads/had-th35...le-hole.20499/

Even this Jegs basic rebuilt TH350 is built to run without the cable.

http://www.jegs.com/i/JEGS-Performan...60300/10002/-1

I would stick with T350 myself. I have a T400 in my 78 TA, I put in 25 years ago. If I were to go through the effort again i would just go overdrive, otherwise a T350 can handle way more abuse than most people think.
I would go with a Continental converter for sure. They work the best in our cars and not expensive...

I Beleive the guy said it was from a 67 Buick. Here is a few pics of the trans. How can I tell for sure it's a BOP??

Chevy case goes to a point at top of case, what pic show is a BOP case.

Not sure on '67 Buick T400's, but '66 Buick T400's take an odd driveshaft yoke that won't slide in typical T400's. Ran across this several times, the first time, many ago after pulling a switch pitch '66 Buick core & spending nearly an hour in a yard fighting to get the yoke off the Buick's driveshaft. Switch pitch t400 will have two spades coming out of the small connector, regular T400's only have one spade.

I used a TH350 behind the 455 in my 71 build....used 36 element sprag, steel drums, HD vasco input shaft etc etc......had a tight built converter design to flash to 3000 under the 455's full throttle torque. can't say enough about how impressed I was with it....plus, I could put my hand on my heart and look my insurance company in the eye and say ..."its all stock".....lol

LOL.. nice.. yeah im seeing more and more comments that the th350 if built right will have no problem to handle that what my engine is pushing. thanks

ok so after digesting the info discussed here i beleive the following is what i should be purchasing.

https://www.tsr-racing.com/chevy-th3...ent-sprag.html

or this are both the same?? or one better then other?? or come with different parts??

https://www.summitracing.com/parts/ati-355682/overview/

rebuild kit # 032905HPSK (super kit)

http://dragtrans.com/dragtrans_html/HPOHK.html

shift kit
https://www.summitracing.com/parts/t...BoCv0UQAvD_BwE


anything else i need to consider??

These are pictures of a ST-300 two speed transmission, not a th-350.

That is correct. This is the same type of 2-speed that came in the '64-'66 GTO & lots of other '64-'69 Pontiac & other GM models. Some GM models used a SP converter.

My tranny guy said he could easily beef one up enuff for my high 11-sec bracket car. But not many guys want a 2-speed, for street use.

Mr. Google will turn up lots of ST-300 info, as well as info on most any other trans you can mention.

https://www.google.com/search?q=2-sp...F9Ew0lPtm2SvM:

Lots of bracket racers prefer a 2-speed, for fewer traction problems at launch, & more consistent ET's. But not many street guys want a 2-speed, although it might help traction, when running the hard street tires, behind a big torque engine. I suppose there might be a very few big cube street cars running a PG.

Thx for info. Bummer. I was gonna try to meet wih the guy to to pick it up. But rather find out now before I get into it and figure out it's not what I need. Thx as always.

In addition to Cliff's th350 book, I've found this th350 rebuild book by Ron Sessions was invaluable. It has great detail on the interchangeability of parts if you are swapping parts from one th350 to another. There are some differences with internal parts from early years to later years. I was using the best parts from several parts transmissions from different years, and could not have done it without this book. I don't know of another source for this valuable interchange info.
https://www.amazon.com/Turbo-Hydra-M.../dp/0895860511

And I bought a th350 rebuild video off of eBay that was helpful too, since it helps to follow along as somebody else does it. It didn't have the interchange info, but a basic take apart, inspection of condition of parts, and put back the same parts replacing wear items like new clutches, seals, etc. It's much easier if you're able to re-use all the hard parts from the original trans that you're working on, and not mixing and matching.

I also referred to the factory service manual a few times, just to double-check some things. With all these references, you'd have all the info necessary to do it. Add a few special tools, and you can do it.

#1 thing to consider is the cooling system. With a more modern cross flow to start with you can probably get a radiator that will handle the extra load of heat. The proper tune up will help lots with the heating issue too.
If you're going to spend the money anyway consider a lower rear gear and a 200-4R transmission. Our 65 GTO has a warmed up 68 400 with 6X heads too. With a 3.55 rear gear on an Eaton posi carrier and the 200-4R you can cruise It at 75 and turn 2400 RPM with a 26" tall tire. You can build it your self or buy one that's good for 600 plus HP.
Have Fun

On cooling my Th350, I chose one of B&M stacked plate style coolers (11" x 11") and did not use the radiator tank cooler. Worked great. If you live someplace cold I might suggest that you have a trans temp gauge and if has issues being too cold in winter, either fit up a thermal bypass or make a cover you can fit over part of the cooler in winter.

Cooling your transmission is another important issue but I was referring to cooling the engine....
As for your idea to use a 400 transmission would not be my recommendation. These transmissions are indeed bullet proof. But due to their heavier internal parts they waste a lot torque just to turn them. The 400 trans would be a great choice for a big block tow rig but wasted over kill for a car like yours. A well built 350 would be my second choice after a 200-4r.

I had my th350 rebuilt years ago with a hardened outer sprag race and heavy duty clutches, and a shift kit. Its still working fine but i worry about the sprag. Some say the outer sprag race is the weak link others say it doesn't help much upgrading it alone. Its been working for me so far. There been alot of debate about the 36 element sprag and how it lubricates for extended street use. Drag racing its supposed to be fine. For street/strip use the 4l6e sprag which is wider and the case saver is supposed to be better. Transgo shift kit gets the nod, however im running and old b&m kit and its fine. The key here is programming the shift so its not too harsh which shocks and breaks the sprag on the 1-2 shift. Once you upgrade the sprag i think the weak link becomes the input shaft. I disabled my kick down, i prefer to take control of my downshifts, i don't like supprises. Might want to upgrade you driveshaft and ujoints while you're at it.

Here is a direct quote i got from Jakes Performance when i asked about the 36 element sprag on the street :

"We know of customers that have run the 36 element sprag on street."

Not real encouraging if u ask me!

See what I mean! Know what your buying because a lot of people don't even know what they're selling. As far as the adapter plate, I have it for my 700

"...There been alot of debate about the 36 element sprag and how it lubricates for extended street use..."


Has anybody used the mechanical diode set-up ? :confused:

http://www.ckperformance.com/View/SU...CHANICAL-DIODE

http://www.yellowbullet.com/forum/sh....php?t=1686522

http://classracer.com/classforum/sho...9&postcount=19

http://www.epilogics.com/md/index.htm

A lot of talk about parasitic drag on a T 400 as compared to a T 350, unless you're running a 10 second or quicker combo drag car, the parasitic drag is negligible between the two. That thought is a quote from Jake himself on his website talking about 4L80E parasitic drag as compared to lighter duty OD transmissions used for performance rebuilds. A 4L80E uses 75% of the same internals as a T 400 has so the comparison is a valid one.

A street car is never going to need the lighter internals to see any difference, lighter internals also have less strength for the same materials used.

Does anyone find it strange that Cliff Ruggles runs a T 400 in his own street car as opposed to a T 350, even though he has written a book about the T 350?

My money is on a T 400 or a 4L80E (basically T 400 internals with overdrive capability) for longevity. The extra beef will have no noticeable effect on performance, but will withstand abuse over the long haul more effectively.

One more point is, to get the lighter duty transmissions to live in a performance environment the hard parts in most cases, need to be replaced with better materials. The stock factory hard parts in a T 400, 4L80E, will live just fine to 750 HP, giving your project room to grow as far as future improvements in your engine program.

There is a reason that the T400 and 4L80E transmissions weigh more to begin with, they have more mass to take abuse from the initial design. They don't need the band aids that the aftermarket has designed to try to make them live in an abusive environment.

I like to do a job one time and not keep re-doing it because the original design was deficient, and the weak link in the chain was uncovered. Spending my adult life in vehicle, stock car racing, and shop maintenance areas, has taught me to remove as many weak links in a mechanical device as possible, and never have to revisit it for breakage. JMO............:)

Other than a slight weight penalty, a stronger transmission platform has no drawbacks that are evident to me.........:noidea:

That said, the OP seems 99% committed to the T350, but he has asked for opinions, and I have stated mine, FWIW.

"...The stock factory hard parts in a T 400, 4L80E, will live just fine to 750 HP..."


Not for the sake of argument, but just to present my differing opinion, I don't think the factory int sprag or roller clutch that came in most Pontiac TH400's will live with that much power. I broke 2 of the stock 16 element sprags, with only about 400hp/500 torque.

My trans guy, at the time, installed what he called a 500 Cadillac sprag, in all my bracket TH400's, and I never broke one. I assume those sprags were about equal to the 34 element sprags used today, for HP TH400 builds.

I would think a slower et like a 11 to 13 second car would actually show the parasitic losses more than a 10 second or quicker car.

Direct quote from Jakes Performance:

I'm sure Jake has plenty of experience with these transmissions to back up his statements.

Also from Jakes Performance:

Jake is probably in the top echelon of aftermarket performance transmission shops in the country. He does acknowledge that a sprag unit can break. The shafts, pumps, drums, and other hard parts will be reliable under 750 HP according to Jakes website. He cites proper burnout procedures as a longevity extender in either T 400 or 4L80E transmissions.