[slowbird]

Just wondering how much one take before it needs upgrades. I am building a new engine that I hope will be between 750 to 800hp and right now my trans is pretty a stock TH400 with good clutches in it. Should I look into having the trans upgraded?

[Polar-Pontiac]

Upgrades are a must with 800hp. IMO

[slowbird]

What type of upgrades?

[mysticmissle]

for sure the sprag, front pump mods, some depends on what year case and components you are starting with. Older units have the capability of adding extra clutches.

[slowbird]

What kills the trans? Is it the launches, when you shift or is it just the power going through it? I do plan on pulling a bunch of timing out of it on the launch so I dont think my 60ft times will be much better than mid 1.5. As you can tell I am not a tranny guy, and can use all the advise I can get.

[mysticmissle]

I have never hurt one. knock on wood. Most of the time its the burnouts that get them. People will give you many opinions on how to do a burn out and what gear to start it in. I think letting off suddenly or powering out of the burnout is the main culprit. I have rebuilt 5 or so now, using TCI or ATI rebuild kits and the HD sprag and no one has had any issues. One BBC blown 8 71 blown nova, who lives to burn his 18" wide mTs hasn't killed his yet. But when he blew it previously he rolled the sprag. but it was very "experienced" in street burnouts. the dogs on the sprag just finally rounded off. no other damage.

[jakeshoe]

Stock TH400 is good for about 400 HP/TQ, it'll take more for a limited amount of time but the 3rd gear clutches will go away.

Some minor (almost free) mods will make a correctly rebuilt TH400 with STOCK parts live at 750+ HP.

Above that I like to use a better clutch (not a "race" clutch) at even the 1200 HP level and the FWD hub needs to be upgraded. With a transbrake the input and mainshaft should also be upgraded above 750 HP IMO.

[Cliff R]

The TH400 can in as many "flavors" as the TH350, and some are better than others in "stock" form. A decent unit before they switched to the intermediate roller sprag deal will hold 500 ft lbs. The type of frictions used doesn't bring anything to the table when it comes to holding up at high hp levels. If the hydraulics holding things well enough, fancy steels and frictions plates don't buy much time, if any at all.

Once we address the intermediate sprag deal, like the TH350, a well prepared (warmed over stock unit) will easily handle 550-650 ft lbs torque and usually good for at least 1000 runs......Cliff

[Schoust]

So Guy's what would you recamend for a street strip rebuild to 750hp? More than likley will never come close to that power but if built right the first time a trans at that leval should last many seasons?

[Kenth]

I like the 1970 Buick and Olds TH400´s, only year with 6 frictions in the direct clutch with sprag type and case saver ring behind center support.
And the 1973-4 Pontiac 455SD TH400 is also built this way.

[Cliff R]

You can take just about any TH400 and install a new 4L80E drum, 34 element sprag, and spiral wound snap ring to cover the trouble with the intermediate clutch set-up.

The later center supports that used the steel shim/spacer are prefered over the older style.

No fancy frictions or steels are required, and one can install shorter apply pistons for increased friction capacity, or use thinner steel plates, machine the stock apply pistons down some, or even get thinner frictions, or combinations of all of the above to get pretty much whatever friction capacity is desired in each clutch pack.

I set them up here with 5 forward, 5 direct, and 3 intermediate. This is adequate with the correct hydraulic program for at least 750hp, probably more.

I don't think it's a bad idea to add more frictions to the intermediate and direct packs, but I prefer NOT to do this by using thinner steels or frictions, they just don't take the heat as well and can/will go out of shape much faster than the thicker ones.

The steels in the fwd and direct drums are available in two thicknesses, around .078" and .090", nearly as I can remember without going out and measuring a few of them?

Anyhow, I much prefer to use the .090" steels in the direct drum, even if it requires dropping from 6 frictions back to 5 frictions. Some builders use the "high performance" red or blue frictions, and kolene steels. Never seen any of that stuff last one second longer than standard steels and Borg Warner or Raybestos stuff, but at least the colors are prettier!

Another nice to know tid bit with the TH400's, the intermediate pack smooth frictions are "waved", not flat like the "waffled" frictions. Most builders go through these units for years, and never know this fact. The waved fricitons may help save the sprag or at least soften the shift ever so slightly, not sure? One can also use a waved steel apply plate in intermediate pack, and Transgo recomends using waved apply plates in all the clutch packs.

Another interesting fact about TH400's is that you NEVER know exactly what you are going to find when you take them apart. I've seen waved apply plates right on frictions, sometimes a waved on a flat steel, different thickness of steels in either drum, or even mixed/matched between drums. Some units will use flat/waffled intermediate frictions, most use the smooth/waved ones. Some units use steel apply pistons, some aluminum, sometimes the check balls are in the apply pistons, sometimes in the drums.

Bottom line is, you'd better be paying attention when you take one apart, and be armed with enough components to correctly assemble it, as at least half of the time they are all over the place by the time you get it!.........FWIW.....Cliff

[Half-Inch Stud]

""""""Another nice to know tid bit with the TH400's, the intermediate pack smooth frictions are "waved", not flat like the "waffled" frictions. Most builders go through these units for years, and never know this fact."""""""

Cliff taught me this like last year or somethin. I went out and took a look and thought geez, them intermediated frictions are waved, albeit at the atomic level.

[jakeshoe]

The .077" thick fwd steels are fine in the directs. I've never had issue using them at even even 900-1000 HP. That said, I agree with Cliff that 5 direct frictions is enough capacity at even 750 HP, and in some cases I use 4 frictions in the directs to free up some parasitic loss on class cars.

3 intermediates is also enough for 700 HP or so. I prefer to go to a 4 pack at over the 600 HP level and I upgrade the friction material at the same time.

A heavy intermediate pressure plate snap ring is mandatory in any build, I always include this and the torrington bearing for the rear in my transmission kits.

The early TH400 drum is considered better than the 4L80E piece (for racing use) if you can find a good one.

I have plenty of the early TH400 drums on hand in good condition so I use and sell those.

It doesn't take anything super fancy for the TH400 to live, but there are some good tricks that help it considerably.

[Half-Inch Stud]

I'm not sold on the Deep Truck Pan, even though they are high quality. Seems a factory depth pan does fine to 9.90's.

I have noticed that the Rear seal may press-fit too lightly in some tail cups. Never had the failure myself butt some folks have posted the dramatic loss of fluid from the rear seal popping out.

[Cliff R]

"The early TH400 drum is considered better than the 4L80E piece (for racing use) if you can find a good one."

I finally ran out of spare early drums last year, and started using the new 4L80E replacment drums. Beats stripping down early cases just to steal the drum out of them. No failures to date, even though it is an offshore part......Cliff

[taff2]

Slowbird,seeing as how your question has be answered I hope you don't mind me tagging this one on- What does it take to make a TH400 live behind a 1200-1400 hp engine,in a light 2500lb car?

[jakeshoe]

Cliff,
The TH400 drum is better because of the way the oil is fed to it, not a material issue.

Funny thing about some of the offshore transmission parts, they work...

Like the Beast shell in the 700/4L60Es, it's a Taiwan part but works great. I haven't had any issues with the Taiwan reverse input drums either.

I think they are making new TH400 pumps offshore too, and I'm 99% sure the aftermarket 4L80 pumps are offshore as well.

If you need some TH400 drums, I can probably send them to you 4-6 at a time for half what you are paying for the 80 drums..
Actually, I need a Q-jet done up and I'm not in a hurry... Might do something there if you want.

[jakeshoe]

Originally Posted by taff2

Slowbird,seeing as how your question has be answered I hope you don't mind me tagging this one on- What does it take to make a TH400 live behind a 1200-1400 hp engine,in a light 2500lb car?

1200-1400 HP...
If this is a transbrake application, you need a 4340 input shaft, mainshaft, and steel forward hub. 6 clutch direct, 4 clutch intermediate, I run a 6 clutch forward, and a VERY carefully setup direct drum with 34 element sprag, or the Super Drum with 36 element sprag. Aluminum takes some load off the sprag but becomes a "consumable".

Torrington bearing between the case and output carrier, and output carrier and reaction carrier since this is where all the thrust loading happens.

If a non transbrake deal, you MIGHT be fine with the stock shafts at your weight.
Little bit of a gamble, but one I would personally take.

[Cliff R]

"If you need some TH400 drums, I can probably send them to you 4-6 at a time for half what you are paying for the 80 drums.."

Thanks, I have several dozen early cases with the smooth drums, but I hate stripping complete units down for one part. I'm not doing too many transmissions these days, shipping prices are rediculous, and we had two units complete destroyed last year by some near sighted moron with a forklift!......Cliff

[taff2]

Thanks Jake.