Hi Folks.
New here, hope to find some help on a Trans issue that has me stumped.
T400 from a 1980 GM 4x4.

Rebuilt with a TCI performance Rebuild Kit, from a couple of years ago, I don't have the part number.
TCI Reverse Manual Valve Body 221201, also from a couple of years ago but Not available any more?
I upgraded to a 4L80 drum and 34 element sprag/clutch.
Both sprag/clutches are in correctly.
Reverse and Intermediate servos Air Check.
Clutch packs are within tolerance and air check.
I DID NOT pay particular attention to end play tolerances.
I doubt that that would cause function issues only possible durability problems.
I intend to do so this next round.

The trans has been in and out of the car 3 times and has never been correct.
Low gear is very sluggish and gets very hot.
2-3-R don't work at all.
+-200 PSI line pressure in all gears ,(I believe that's normal for this valve body?)

I used the Cliff Ruggles book combined with instructions from both the rebuild kit and the valve body.

I know I am probably missing something completely obvious, but its sure got me scratching my head.

This is in a rock crawler, LQ9, 2600 Stall Converter, tube chassis, blah blah....
Relatively easy to pull in and out.

Appreciate any help/advise!
Thanks!

 

What did the TCI instructions tell you to modify?

Do you have a cast iron valve-body? Do you have a billet aluminum valve-body with engine braking?
If you have a cast iron valve-body; then most likely the transmission should not have the intermediate band installed...

I wonder if you may have mixed and matched build procedures from the TCI instructions with the Ruggles book.
There is a very good chance you made a build error and have the corresponding circuits leaking.

Nobody wants to hear this... But, the best thing to do is take it a part and double check the instructions.
Fortunately the THM400 is one of the quickest units to disassemble.

 

Valve Body Mods included leaving out a few specific rings and seals along with changing springs in the servos and Front Pump.
The Valve Body itself is a factory style Iron Casting that TCI modifies.
The Valve Body was supposed to have braking in all gears, this would require the Intermediate band,,,No?

The trans has been out, rebuilt and back in 4 times in the last 3 weeks.
I am unable to find any issue with assembly, that's why I came here.

It is easy to remove and reinstall due to the tube chassis.

Thanks!

 

Mod valve...is it oriented properly and I'm assuming there is a modulator plug??
Post the instructions and if you get it apart, post a bunch of photos.
I'm not familiar with the TCI modifications, so standard troubleshooting doesn't really work lol

Center support bolt is the first thing that jumps to mind with no 2-3-R

 

Hmmm,
I have not double checked the Modulator Valve Orientation since the original rebuild.
I will make sure to check that when the trans comes back out.
Plug and Bring are in place.

Center Support bolt was torqued to spec. after alignment of the Center Support.
Air checked OK.

I appreciate the feedback.

 

So,
Pulled the Trans again last Saturday.
Modulator Valve was in place properly.

I pulled the Valve Body and installed an FTI-F4008.
Instructions are identical to the TCI-221201 with the exception of removal of the intermediate band, removal of the Intermediate Servo Piston and spring and check ball/restrictor cup location.
Took an hour or so to re-install,,,,,

GEARS!
I've got GEARS!
All of them, it seems.


Installation Note;
I did notice that the Reverse Servo cover interfered sligtly with the new Separator Plate
VB Bolts did not align properly.
I ground away a small portion of both the separator plate and the servo cover for clearance. Approx. .040 from each.
(I checked the TCI Separator Plate, It did not have the interference issue)

I won't have time to test drive for a week or so as I'm gone on business, but it function tests great in the shop.
I'll report back as I get more info.
​​​​​​​RS

 

You didn't find that a build error was made, when you went to install the new valve-body?

Have the old valve-body vacuum tested...

 

You're not the same guy I saw on fb posting about this VB and complaining about the instructions are you......

 

Nope.
No FB posting here.

The instructions COULD be better, for the inexperienced builder,,,, TCI especially.
I suppose that a person SHOULD study up and learn the how, what and why of a transmission before diving in.
But, heck, I built the entire rig from a pile of tube. New Cam, valve springs and all that in the LQ9,,, why shouldn't I build the trans too! Yeah, Right!
Do they have a beginners rebuild manual?

I used the Cliff Ruggles book, which was a tremendous asset.
I'll be grabbing the ATSG manual as well, to learn more.

If anyone can recommend other literature that might include Dos and Don'ts id surely appreciate it.
How about the flow path and circuitry to activate each gear selection? Couldn't find that online.
Of course, there is no substitute for experience, and mistakes, for any learning experience.
I'm here, learning.

Have a great day guys!
RS

 

For an aftermarket valve body...you're on your own. Get the case, the separator plate, the VB, some markers, and your favorite beverage. I'm a root beer kind of guy but to each their own

Take the time tracing from the suction port on the pump...and go from there. Trace where everything goes. It's a process.
Its really fun when you get an unknown/unmarked VB in a trans that's been giving someone else issues...and you have to reverse engineer how **** works and what the issue is.

 

lf your trans shifts automaticly make sure the trans gets 12 volts when at full throttle.