First a little back story and then I'll get to the actual reason for this post.
I built a TH400 for a friend of mines shop a while back. It was for a good friend of his that he has raced with in the past.
It's a HD case and a 6 bolt pump. We used an FTI trans-brake, FTI forward drum/input shaft, FTI forward hub and output shaft. We used straight cut gears. I used blue Teflon rings on the pump for the forward drum, the 4L80E peek rings on the center support for the direct drum.
The customer said it worked for two burn outs and 1 run. I now has only reverse, no forward, no trans-brake. So, this leaves me to believe that the forward clutch is not applying. My shop owner friend tells him to bring it back and we will look at it.
Today I took the FTI VB off and air checked the trans as best I could.
Man I wish I had a Air test plate for a TH400. It air tests good for what I can actually test. Intermediate clutch, reverse band, direct drum and forward all seem to apply just fine.
We decided to tear it apart for a broken part. We find nothing bad or broken. I air tested each component on the bench and all tests good again.

So here it the real questions. It appears to be a GM rebuild with a 9MA code painted on it.
1) does anyone know what a 9MA unit is from?



2) When I took the center support back out, I noticed something that makes me think is it right or wrong?
I remember a late narrow lug center support that uses a snap ring in the case to keep it from wearing the case and an wide early version that I try to never use. I remember a lip on the rear where the front sun gear bearing race rides. The one I pulled out looks like a late 4L80 one that has the shim under the rear sun gear bearing. It has a normal 400 busing and no hole for a center lube feature so it's a genuine TH400 or early 4L80E center support. I rollerized the rear case washer and remember setting up the clearance. It did not lock up the gear-train. Maybe I'm just confused or paranoid...
here is the one I took out.


here is a old 400 center support that he had on the shelf

 

No idea on the number, But See no issue with center support. Were the FWD CLUTCHES BURNED? That is the common link between brake and fwd gears. You have rev so we know band applies and holds. The direct clutch is used with the brake but cannot hold anything without the FWD CLUTCH. Low roller is good or at least not the issue as the brake applies the band-direct clutch and of course the FWD CLUTCH is on.
I have been into one of those valve bodies and check that all the set screw plugs are in place. Had one come out once near the manual valve and caused no forward or brake. May be in pan. If so do not screw in to far will damage or stop the MANUAL VALVE from moving.
Since it did work initially and description you give about has to be .
1-FWD CLUCTH DRUM OR SEAL ISSUE. (IF ALUMINUM PISTON THEY ARE BAD TO CRACK ALSO I ALWAYS REMOVE THE INNER SEAL ON DRUM)
2-SEALING RINGS PUMP TO FWD CLUTCH (I PREFER SCARF CUT OLD STYLE HERE PARTICULARY IF A REMAN DRUM )
3-PIPE PLUG CAME OUT OF VB AT MANUAL VALVE
4-SOMETHING BLOCKING FWD FEED IN PUMP OR VB (While I have not seen this with a 400. I did run into it where we have a guy wearing gloves I was training to build. We got trans on DYNO "4l60e" intermittent neutral on the 2-3. Took a bit to figure out but that glove piece was in the groove for the 3-4 clutch feed on the shaft and was traveling around it occasionally being in just the right spot to bloc the feed to the 3-4 )
5- And of course make sure your bottom steel or wave in fwd is not getting caught in grove in drum just above piston if using the aluminum one. Thing steels or later thin wave plates can do that with the 400 . Cant happen with molded pistons.

Hope helps some . Not really alot to the VB as far as function , It is pretty simple other than the bore plugs coming out nothing much really to go wrong with it.

 

Thanks for the feed back Frank.
I didn't think there was really anything wrong with the center support. I thought I was just being paranoid or overly cautious. You know how it is when you are looking for "what's wrong with a build".
The forward frictions were like new. The forward drum air checked well over the pump but I did not have a 40psi air supply, only shop air. I will get my portable regulator for when I go back. (my personal build area is a bit better laid out but if he calls for help, I go to his place.)
1)I think it had a 4L80 aluminum forward piston. I don't remember if I left the middle lip seal out of the drum or not. I know GM just puts it there to slow the apply rate and I typically leave it out on a unit like this. I will double check that.
2) I'm using the blue scarf cut teflon rings on the stator.
3) I did double check the allen plug in the VB. I also put a finger over the end of the bore as I pulled on the manual valve and it pulls suction on my finger. The FTI VB has no valves whatsoever. It's just a machined block of aluminum, it's quite the piece of art.
4) I double checked all the forward feed holes through the stator and drum. The forward drum is also quite nicely machined for a hardened shaft with a much larger drum spline.
5) Pretty sure I put a thick steel in the bottom of the forward drum. I have run into the thin steel getting caught in the bottom grooves before.

I will double check all the points you made above.

I did ask to see the external shifter lever, the corners of the manual shaft are beveled slightly. My thought was that it has a narrow lever that wouldn't fully tighten and actually wollered out the hole and it never really moved the manual shaft.

 

MA = HUMVEE Unit.

Most likely 1989.

 

Thank you!
That's what I was told. I just don't have a code list for the TH400. I have one for the 700R4, 4L60E & 4L80E.

 

I have had so many issues with those converted iron valvebodies, I no longer use them and now turn away customers away that insist on them. I spent a lot of time and effort trouble shooting one, Vacuum testing and replacing plugs and valves one by one without any cure, only to ship it to a friend in TX with a hydraulic VB dyno and find a hairline crack in the manual valve bore. The avarage 400 iron VB casting is 50 years old. That any of them work correctly is a testament to the engineers of the old school.

I do realize that leaves no foward pattern auto shift transbrake units out there but those folks will just need to find someone with more capacity to fool with them.

The reverse pattern one is just awful. The entire feed for high gear going through that set screw....yikes. Charlie at ATD calls them "high gear killers" haha

 

Thanks for that information. I would agree that the cast iron VB are old and not worth the time to work with them for a trans-brake. I no longer use cast VB's for anything but stock style builds with a mild shift kit myself. If they don't want to spend the extra $$ they can go somewhere else.
Just an FYI and because I didn't specifically state this.
This is a FTI sportsman billet aluminum trans-brake. It is part # FT4009B
https://ftiperformance.com/products/...ebody-kit.html
The price is pretty fair @ $499 as of 9-1-2025

 

I'm not sure why would feel the need to mention any older converted transbrake valve bodies... the OP already stated its one of our billet aluminum valve bodies, which all of our transbrake and even reverse pattern non-TB valve bodies are now aluminum.

considering the context of the thread I really hope this isn't attempt to talk down on our older iron transbrake valve bodies, please feel free to correct me if I am wrong?

-Dalton Samuel @ FTI

 

The shop owner tried to lay some blame on the VB but I quickly dispensed that. I showed him how the VB is machined with 4 mounting bolts and how the manual valve moves fluid. You can see the precision in all the passages.
I spoke with one off the techs at FTI. The customer service was very good. I needed to confirm the size of the check-ball. He didn't actually have the answer but called me back within an hour confirming my thoughts.
After I assembled the unit it air tested very well.
Right now I believe the manual lever is to blame.
I'll post the root cause, when I figure it out.

 

I really do not think @truckdoug was saying anything about FTI products at all.


I believe he was just saying that these converted OEM Valve-Bodies end up being far more problematic down the road, compared to modern offerings.
I mean half the time I take them off of a Core, they are warped and the Valves are sticking... or are completely stuck!

Also, I get to hear from him a little bit via text message, and I always hear him praising both FTI and Independence!
Especially in his YouTube Videos! He is a pretty Rad Dude!


Also, @FTICONVERTERS You are another guy in My Father's Phone Book that he wrote was great to do business with.
Nice to meet you!


I am finding out that the High Performance Auto. Trans. community is a small world!
I even see @Tranzman on FaceBook, Posting in the THM200-4R Groups!

 

Thank you for the awesome feedback @Tranzman ! We are human but we try our best to take care of everyone. Feel free to PM, call, or e-mail as well if you need anything.

-Dalton

 

I must say I have used many of the FTI aluminum RMVB with brake over the years and they are my go to when someone wants this on a 400. They are simple to the point and do the job with minimal additional mods. And I have a FTI triple disc 2800 stall in my 95 impala ss 35k miles thus far and very pleased.
I also try to push my customers to 1st FTI - Yank or Circle D as I get frustrated with these JEGS / SUMMIT converters and of course EBAY made by GOD KNOWS WHOM and since I have been doing this at home out of 300 units thus far I have had a total of 5 comebacks 3 of which were converter failures of the cheap units available on those sites. 2 of them just virtually immediately delaminated the lockup clutch and one of them just got so hot for some reason it literally melted down the plastic parts of the pump and melted the paint off the converter itself (in less than 10 miles !). Sadly people still buy them though.
So as RULE and also being a fellow sponsor of the forum here my first suggestion is FTI and because I have the most experience with them.
Note with these EBAY, JEGS, SUMMIT brand converters. I do not know who makes them or what Summit for example pays. But I did know a fellow builder who Contracted to do some 700r4 for them and here is what I learned. They pay like 800 to do a unit parts and all and then they call it a stage 2 and charge like 1800 for it at the time. No way you are getting much of a trans for 800 dollars. So Buyer beware on trans or converters listed as HOUSE BRANDS on their sites.
Unsolicited commentary sorry .
Again my experience over the years with FTI has been nothing short of excellent.