TH400 Rebuild tips

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington

Attachments

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington
View attachment Scan0040.pdfView attachment Scan0041.pdfView attachment Scan0042.pdfView attachment Scan0043.pdfView attachment Scan0044.pdfView attachment Scan0045.pdf These last two pages are very good advice for any rebuilder. Sonnex makes extremely good performance products as does Coan Racing. There is also a few good suppliers I'll post later.
There is a really good rear bushing and thrust washer that I have used and also a Torrington bearing (in place of the bronze washer) that I will also post about.
In all my transmission builds I strive to keep the tolerances as tight as possible.
The rear end-play as close to .005" as possible, and the front end-play as close to .004" as possible. This means that all the thrustwashers need replacing as does the Torrington bearings. This gives the transmission the best chance for a long life as possible.
 

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington
013.jpg015.jpg014.jpg009.jpg016.jpg018.jpg019.jpg

These are some pictures of a Heavy Duty TH400 case. The first 2 pictures shows the 8 bolt holes for mounting the front pump assembly (TH475 models only) . The third and fourth pictures show the extra strength on the flange to mount the aluminum torque converter cover and the support it provides for the transmission. Note the brace-rods going from the cover to the engine mounts. Pictures five and six show the raised numbers "39" which says this is a Heavy Duty case. Most cases with the raised numbers on them are Heavy Duty cases. They are made with extra thick housings and flanges. Usually the raised numbers are 30's or 40's numbers.
The last picture shows the holding brackets used in repairing the GM transmissions. I highly recommend you find some if you plan on rebuilding more then a couple GM transmissions. The black one is for the older transmissions stopping at the TH400. The blue one is for the 4L80E to 6L90E transmissions.
Most all the military TH400's have been the heavy Duty models though I have seen some M1008 units that where not. Most all do not have the 8 bolt pump mounting though. That was used on the TH475 models only. I have been able to drill out the pumps and housings to make them the stronger TH475 units though.
If anyone is interested I will post some pictures showing how this is done.
I will be posting some pictures of the performance parts that will increase the durability of the TH400 later. My camera's batteries crapped out on me when I was taking these pictures.
 

patracy

Administrator
Staff member
Administrator
13,803
1,116
113
Location
Buchanan, GA
Thanks for the info. I happen to have a TH400 on the bench waiting to be serviced. Might just rebuild it while I'm at it and beef it up. It's going in the M114.
 

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington
004.jpg005.jpg006.jpg008.jpg010.jpg012.jpg013.jpg014.jpg018.jpg021.jpg

Picture one shows a 32 sprag unit for the intermediate clutch assembly. Picture two shows a special "Torrington" bearing used in the bottom of the case instead of a bronze thrustwasher. Picture three shows where to mount the Torrington bearing. Pictures four and five show the differences of the different performance clutches you can use in the forward and direct clutches. Four shows the ones from a AT540 direct clutch which fit in the direct and forward clutches of a TH400. They are made from an Asbestos material so I'm not sure they still are available. The fifth picture shows the "Red Alto" clutches used in performance trans today. The sixth picture shows the Extreme duty Kevlar intermediate band. The other band is a Red Alto lined band. You can see the extra metal and welds used on the Kevlar band. Some say that this band will dig into the direct drum more reducing longevity of the transmission. I haven't seen this myself though.
Picture nine shows a piston that has been machined to allow 6 clutches in the drum. The last picture shows the differences between the direct and forward pistons. The piston for the direct drum must have a drain check valve. The forward drum has a built in drain check valve so it doesn't matter what style piston goes there.
 

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington
View attachment Scan0046.pdfView attachment Scan0047.pdfView attachment Scan0048.pdfView attachment Scan0049.pdfView attachment Scan0050.pdfView attachment Scan0051.pdfView attachment Scan0052.pdfView attachment Scan0053.pdfView attachment Scan0054.pdfView attachment Scan0055.pdfView attachment Scan0055.pdf

These are just a few performance items you can add to your TH400. I usually add these to all my performance builds including a few others I didn't mention. Like "300M" input and output shafts or Aluminum drums or case reinforcers. Needles to say you can spend thousands of dollars on performance parts ! You can build a transmission that can withstand 2,000 HP if you have the money ! I prefer to build more modest units though that can handle 800HP on a daily basis.
 
Last edited:

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington
The TH400 is a great transmission in it's stock configuration though there are trouble spots. The designers built a great gear train here, but to make the trans more appealing to the masses they went with a poor design for 2nd gear. It allows a very smooth transition from 2nd to 3rd gear by using a oneway clutch (intermediate). This means instead of a solid part like a band attached to the case (like Chrysler and Ford did) they used this oneway clutch attached to a case support. By doing this they only allowed for 2 to 3 clutch plates to hold the gear and a small oneway clutch. We need to reinforce this area to make our trannys last so we add a 32 sprag instead of a factory 16 sprag, and try and increase our clutch area by adding more plates. "Coan racing" did this by making a special piston that was machined down to allow another plate. Also by going with the special "Red Alto" thin plates we can add up to 7 plates here if needed.
I always use "Kolene" steels in all my rebuilds now. They are a special hardened steel that is thinner (allowing more plates) and more durable then stock steel plates. They also come in different thicknesses so you can adjust your clutch pack clearances.
Some of you might be wondering why I'm giving away my "secrets" to rebuilding the TH400. I was recently "forced" to take a Medical Disability Retirement. This means I can no longer work for money ever again ! No little side jobs to help buy that Deuce part or help with the home. So there was no reason to keep this to myself any longer. There is a ton of stuff I haven't mentioned yet, like how to bolt together the pump without the special tool or how to put on sealing rings or the how to adjust the gear unit assembly for the tightest possible tolerances. That means I will be rebuilding a TH400 for the camera, and if I do that I might as well really do it. I don't have the space right now since I'm working on all my deuce projects but eventually I will get that done and can come back and add more to this post.
 
Last edited:

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington
022.jpg025.jpg

I had more pictures to upload but the system is not allowing me too.
Anyway the first picture shows the 3 types of intake pipes used. The first is for the deep pan and the last two are standard pans. The metal one is the most desired since it will not crack due to heat fatigue. The next picture shows a special rear housing bushing from "Sonnex" that has a shoulder to prevent it from walking out the case. This is a rare phenomenon that is due to a worn case or to much gear clearance causing the gear unit to move back and forth excessively. I use it in a reversed configuration to hold my Torrington bearing in place.
When I can upload more pictures I will.
 

tourus

Member
197
2
18
Location
madison me.
I have been following this post. But I have one quick easy question all these up grades are great.. how user friendly is the trans. going to be after all this.. for every day use and work.. example I plow a lot of snow, tow a 24 foot goose neck trailer. with what ever on it,, like yesterday hauled 3 ton of coal on bed got a real good buy on it. 3 pallets. 25 miles.. play in fields in winter . and out on ice in winter things like that will it last 100,000 mile or so.. with good service and filter changes .. then use every day to go back and forth to work..
don't get me wrong I am following this and do like it I am always looking for up grades to stuff and to make things better .. thank you very much for posting all this information .. and for your time in doing this..
I am not in any way putting this down just wondering .. also I hope this goes to the sticky notes when you are done so I can refer back to it when I rebuild my next transmission.. I also hope that this reply can be removed before it goes to sticky's..
 

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington
I have been following this post. But I have one quick easy question all these up grades are great.. how user friendly is the trans. going to be after all this.. for every day use and work.. example I plow a lot of snow, tow a 24 foot goose neck trailer. with what ever on it,, like yesterday hauled 3 ton of coal on bed got a real good buy on it. 3 pallets. 25 miles.. play in fields in winter . and out on ice in winter things like that will it last 100,000 mile or so.. with good service and filter changes .. then use every day to go back and forth to work..
don't get me wrong I am following this and do like it I am always looking for up grades to stuff and to make things better .. thank you very much for posting all this information .. and for your time in doing this..
I am not in any way putting this down just wondering .. also I hope this goes to the sticky notes when you are done so I can refer back to it when I rebuild my next transmission.. I also hope that this reply can be removed before it goes to sticky's..
I've done most of these mods to my personal M1030 truck (or is it a M1034 ? can't remember) and it works great. I can use it to just tool-around or haul 2 tons of sacked concrete. Some people don't like the firm shifts, but it is reassuring to me that all is going well in the tranny. Of course I have also built a TH400 for a guy who was drag racing in the low 6's . I really didn't think a 3 speed transmission would be good for such a fast car. I mean you'll be shifting into 3rd gear past the finish line ! Actually I adjusted the shifting points to match his torque curve and it really worked well. Of course most people don't need a transmission shifting at 5,000 rpm's ! or a torque converter with a stall speed of 3,000 rpm's either.
The main reason to do any of these modifications is durability and longevity of the transmission. I had built a TH400 for a 1972 GMC 3/4 ton truck in the early 1980's. Last I heard the truck was basically destroyed but the transmission was still going strong. Build it right with the right parts and you can have a good and faithful transmission for decades to come.
That is why I posted this information here.
 

tourus

Member
197
2
18
Location
madison me.
OK great I am going to watch this more to see what else you have to say.. I myself like a real good firm shift .. I do have on more question about the transmission .. (400) . I have seen video's about drill out the spacer plate.. to make it the same as a B&M shift kit.. have you ever done that your self or have you just bought the B&M kits.. also what other up grades can people do to the valve body .. I have put in new "up grade spring" quote shift kits. and what can we do to the front pump..

I have also been told that the planetary gears and the front pump out of a 545 Allison will fit do you know or is it just the clutches.. what else could be used as I do have a good working 545 out of a old bus in the garage on the floor due to the fact I was told a lot of parts are inter changeable. am going to conbind them.
 

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington
OK great I am going to watch this more to see what else you have to say.. I myself like a real good firm shift .. I do have on more question about the transmission .. (400) . I have seen video's about drill out the spacer plate.. to make it the same as a B&M shift kit.. have you ever done that your self or have you just bought the B&M kits.. also what other up grades can people do to the valve body .. I have put in new "up grade spring" quote shift kits. and what can we do to the front pump..

I have also been told that the planetary gears and the front pump out of a 545 Allison will fit do you know or is it just the clutches.. what else could be used as I do have a good working 545 out of a old bus in the garage on the floor due to the fact I was told a lot of parts are inter changeable. am going to conbind them.
First the only parts that are interchangeable are the clutch plates like I mentioned earlier. Nothing else fits. To make the pump work better there are new bushings with a poly coating that last real will, also harder gears you can buy. As far as a kit goes I have never used one. I always drill my own separator plates and valve bodies. In my first post you should have seen my cheat-sheet on where to drill and what sizes to drill too. I really don't like messing to much with the factory springs on the shift valves as there are so many variables to consider. They already did the work so why mess wit hit ? I do believe in increasing line pressure though which is really easy in a TH400. You just add shims to the regulator valve in the pump housing. I can show you that later if you want. I also believe in using the "maximum" amount of return springs in a clutch housing. You want to eliminate almost all "crossover" of applying and releasing clutches. The longer a clutch is holding on while another clutch is trying to apply creates wear and tear on the unit. The closer you an get to "zero" overlap the better.
That is why the "Linko" manual transmission is used in racing so much. It is basically a automatic transmission without the automatic part ! They use bands to hold the clutch housings on each planetary unit. You pull each lever in sequence as you go. No overlap ! There are upgrades to the valve body itself, but that is usually for full racing only. Unless you like shifting at 4,000 to 6,000 rpm's I wouldn't do them. There are a bunch of "shift softeners" incorporated in the TH400 that I always eliminate. Again no overlap wanted. I can show you where to drill and tap the valve body.
 

rustystud

Well-known member
8,487
150
48
Location
Woodinville, Washington
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks