Rebuilding/Beefing a TH400?

[Hossbaby50]

I picked up a TH400 today that I am going to have rebuilt sometime. I am wondering what all I need to do to get a little extra beef out of the TH400. I know it is stout to begin with but I want a little extra. Nothing that is really expensive but what can I do that is good bang for the buck upgrades?

I am not looking to go to things like straight cut planetaries or the 2.75 1st gear, just things to make the tranny last longer and take more abuse.

The setup I am currently thinking of is a full rebuild, reverse manual valve body, and low stall TC (800-1000rpm). I rock crawl my truck, that is why I have want such a low stall converter.

Is there any way to increase line pressure to get more holding power on the clutches? Are there stronger bands and clutches available for a good price or are quality stock replacement parts good enough. The Th400 will be living behind a mild TPI 350 that has some decent low end torque. It will have a NP208 case and 3/4 ton's with lockers and 37" tires. I want to be able to beat on this tranny if I feel like it and not have to be scared of it like I am of my 700R4. I already have 2 external coolers and an external tranny filter so cooling and filtration are not a worry. Thanks

Harley

 

[Ryan B.]

Is there any way to increase line pressure to get more holding power on the clutches?

A shift kit will raise the pressure, i'd definatly reccomend putting one in.
A full manual valve body will raise line pressure to the maximum. even higher than a shift kit i believe.

you could upgrade to a 32 element sprag or whatever for greater torque handling capability, but i'm not sure thats even necessary. i rebuilt my th400 for my camaro and used B&M's master racing overhaul kit, and a tci reverse manual valve body.. and its held up to over 500 ft lbs. for a couple years.
i'd suggest going with an art carr manual valve body though so you can keep compression braking in 1st and 2nd gear.
Th400's are pretty stout.
Also, 400's are the easiest tranny to rebuild of all GM autos. You swapped over to tpi, i'm sure you could rebuild your own tranny with an ATSG manual.

 

[dirtwarrior17]

took the words right out of my mouth...

I have a shift kit and all the corvette stuff on my 700 and theres a HUGE difference.

Also th400's are really easy to find deals on... my dad had his built to handle 600+ hp for about 1000 bucks.

My brother threw it in reverse at 60 mph and it locked up the tires, kicked back into D and kept tickin.

Go look under some monster trucks... what will you find? A th400.

 

[Hossbaby50]

How much are the Art Carr manual valve bodies? The B&M is only $150. I know Art Carr makes good stuff but is it really worth the extra money?

Harley

 

[Nonesuch]

There are tons of hop-ups for the TH-400. One of the easiest things to do is adding more cooling capacity to the system. Of coarse the first thing that pops into your head is a stacked plate tranny cooler. Good mod but not really all you can do.

The direct clutch hub can modified to add cooling capacity to the clutch stack. The stock drum has 'x' number of holes. B&M recommends adding 25% more holes, 3/16" and increasing the stock holes to the same 3/16". The same thing applies to the forward clutch hub. You can further reduce the heat in the foward clutch by using .0915" steels instead of the stock .0775" steels. If you do use the thicker steels, make sure you don't exceed the minimum clearance of the clutch stack. The acceptable range is .030"-.070" with .030"-.045" being ideal. The tighter the clearance in the forward clutch, the firmer your shifts will be. Firmer shifts also mean less heat.

This one costs a little money but it's highly recommended in racing or heady duty use. Upgrading to a 34 element intermediate sprag. This mod increases the stock sprag/clutch capacity about 110%. To do this mod you have to make sure you A) don't already have it or B) can get your hands on the required mid 1971 year model TH-400 direct clutch drum (or earlier year) or an aftermarket version.


These are just a couple of mods out of many. I don't have these memorized or anything. I pulled the specs out of a book. I recommend you get yourself this book if you want to learn all about a TH-400 and all of the mods you can do to it. You may even decide to tackle the rebuild yourself after reading through the whole book. It's not that hard to do. Oh by the way, be careful in which full manual valve body you choose. The Art Carr is the best but can be very tricky to install. I have one and I love it but it cost's near $400 dollars. www.artcarr.com
Here's the book http://www.motolit.com/0879382678.html

 

[dirtwarrior17]

Sorry hoss for the OT question but is there an OD th400 or a kit to put OD in one?

 

[Nonesuch]

Sorry hoss for the OT question but is there an OD th400 or a kit to put OD in one?

No, but you can add an overdrive unit to the back of the trans. The downside is the added length.

 

[1979jimmy350]

there is a overdrive version of the 400 it is a 4l80-E. The only proble is that it has electronic controals

 

[dirtwarrior17]

now lets get back OT.

 

[Nonesuch]

I was replying 'no' about a kit to put OD in a th400.

I didn't even consdier the 4L80e. It is very similar to the th400 but was a complete re-engineering of the original. A very strong transmission but too damn many electronics.

 

[Hossbaby50]

I currently have 2 B&M stacked plate coolers (1 24,000lb GVW & 1 19,000lb GVW) on my 700R4 along with a PermaCool remote tranny filter. These items will be kept in place with the Th400 when I install it.

This is not going to be a race tranny or see constant abuse. I just want to be able to abuse it if I feel like it every once in awhile and not have to worry about putting the hammer down on it.

Harley

 

[moneypit]

I broke my th400 in 2 pieces at Penrose...... Didn't even know it, heck I drove it out and didn't notice for a couple of weeks. Art Carr is a pain in the A$%. I now have a working reverse pattern manual valve body. I pulled the valve body 3 times last summer before I went back to stock. This time I pulled the tranny twice after tyhe rebuild cause they insisted it wasn't the valve body. Guess what they sent another and this one seems to work. That makes 3. Needless to say I haven't wheeled with it yet so until I do I don't think highly of them. If someone else made one with compression braking I would have bought a different one. This became my expense that they could care less about. They did make it right though, just not financially. I will tell you the whole story when you get back and by then I will have wheeled it and will be thinking it is the shiznit........ BTW they sent AN EXTRA VBODY......

 

[Hossbaby50]

So you have another manual valvebody? Does it work? How much? I am going to start gathering parts for this project and probably have Wendell put it together for me when I get up there and established a little.

Can you explain the compression braking thing to me? I am wondering what exactly it is. I know about compression braking in a manual, and I get some compression braking with my 700R4 with the low gears in my 208 & 4.56's.

Valvebodys from B&M and such don't have that or does the Art Carr have something else above and beyond normal valvebodies?

Harley

 

[ntsqd]

Something I was told but do not know if true or not is that the 1 tons got what is refered to as being a TH475. The difference is at least one more steel and organic in each (?) clutch stack. Would be worth looking into.

FWIW I know three Pro trans guys and none of them will use anything from B&M except for maybe their shifters. All three work in different areas (one 60 miles away) so it's not like they got together and decided to shun B&M. All three only use the Trans-Go kits.

 

[Ryan B.]

Can you explain the compression braking thing to me? I am wondering what exactly it is. I know about compression braking in a manual, and I get some compression braking with my 700R4 with the low gears in my 208 & 4.56's.

Valvebodys from B&M and such don't have that or does the Art Carr have something else above and beyond normal valvebodies?

Harley

The TCI and most other manual valve bodies have no engine braking in 1st and 2nd gear. The instructions actually tell you to disassemble the transmission and REMOVE the second gear band and one of the seals on the center support in the very middle of the tranny. The 'valve body' and its description makes you think its an easy task that you could do with it in the vehicle and you don't have to tear the whole tranny apart.
Imagine you'll be cruising on the freeway, take your foot off the gas, then drop it into 2nd.
Usually it would yank your truck into the downshift and start slowing you down pretty quick. Well with no engine braking when you drop it into 2nd with your foot off the gas it will go from freeway cruising rpm down to idle. then when you romp on the gas it will free rev up to the appropriate rpm that 2nd gear will catch at. Cool for racing and downshifting, but not that great for other than a race car.
On the trail i usually keep it in 1st to keep me crawling going down hill. It would be pretty scary when all you have is the brakes to hold you.
Thats why you should go with a manual valve body that retains the compression braking...
Otherwise you could get a B&M shift kit for like $35 and it will bump up the line pressure like you want, and it will still shift for you if you ever drive on the street with it in D (3rd).

 

[Hossbaby50]

Thanks, that is what I needed to know on that. So no manual valve body unless it has the engine braking. I may just stay with the normal valve body and shift kit if I can't find an Art Carr or one with EB for a good price.

I thought TH475's were in over 1 ton applications like motorhomes and stuff. The TH400 I got is from a CUCV 1 ton (I think)

Harley

 

[Ryan B.]

Something I was told but do not know if true or not is that the 1 tons got what is refered to as being a TH475. The difference is at least one more steel and organic in each (?) clutch stack. Would be worth looking into.

FWIW I know three Pro trans guys and none of them will use anything from B&M except for maybe their shifters. All three work in different areas (one 60 miles away) so it's not like they got together and decided to shun B&M. All three only use the Trans-Go kits.

One thing you can do is measure the clutchpack clearance that you currently have, then pull it apart and measure each friction/steel..
You can order thick and thin steels and possibly friction plates also. so if you do some math combining thick and thin plates you might be able to sneak an extra clutch friction/steel in there as long as you have proper clutchpack clearance.
For example, if you originally had 4 thick clutches, you might be able to order certain ones where 4 thins and one standard thick friction/steel will get you an addtional clutch but the same clearance.


I've installed a few B&M tranny kits, one TCI valve body, and one transgo... my experience was that the B&M installation instructions walked me right through their kit. With the transgo kit on a 4l60e they had a couple parts where the instructions and pictures where very vague as to what you were supposed to do. There was a valve in the valve body that you had to put a clip into, and it didn't really tell you what passage the clip went into, we pretty much guessed and hoped for the best on that part..kicking oursleves in the arse that we didn't take pic's of it before taking it apart.. figuring the transgo instructions would be detailed enough.. we must have done it correct because it worked out in the end. but my experience was that transgo instructions were the worst compared to B&M and TCI.
I'm always hearing the same thing that good shops hate B&M parts and will only go with transgo stuff...
What is a shift kit? A new seperator plate that you drill some holes in depending on if you want stage 1 or stage 2. a couple of springs to go in the valve body and maybe the main prv valve. thats about it. A metal plate and a spring or two. maybe leave out a check ball. pretty easy stuff.

 

[az-k5]

I thought TH475's were in over 1 ton applications like motorhomes and stuff. The TH400 I got is from a CUCV 1 ton (I think)

Harley

They were, they had strait cut gears, and some different bearing designs on the shafts. They are les likely to frag, but the strait gears do build up heat faster/easier. I don't know if the gears are wider to make up for the loss of tooth surface area (I am about to lose you harley) or the single point loading of the gear tooth makes up for the loss of mass and subsuquent loss in strenth.

 

[mrk5]

Funny you'd should bring this up, Harley. I'm thinking real hard about rebuilding my TH400 this fall.

My father-in-law and I did a rebuild on my 400 a few years ago. Wasn't too hard. We made a couple of rookie mistakes, actually just missed torqueing a couple of items.

I want to do it again because I would like to upgrade to the lower 1st gear and install a TCI manual/automatic valve body. I don't want to do the full manual because I want compression braking. Especially for driving the highways in the mountains. And it sounds like the AC valve body is way more trouble than it's worth. I had heard something some time ago that TCI was supposed to be coming out with a full manual valve body that has compression braking.

 

[dirtwarrior17]

ditto on the th475... they came in motorhomes and large trucks.

my dad was looking at a motorhome with a th475 in it stock.