Well lets start by asking which gears you still have
and if you left the ring off of the 2-3 accumulator piston in vb ?

Drilling a hole in the plate ?
As long as you followed the instructions and can verify you drilled the right hole, then you'll be ok to forget about it. Without a picture, We have no idea what hole you drilled and cannot answer your question as there are lots of holes and usually you would open up 2 holes or more.
I. am assuming your missing 3rd gear, ??
If so, here are a few questions?
Are you getting at least 12 inches of vacuum to the modulator?
Did you forget to tighten the 12 pt 3/8 center support bolt?
did you put the center lip seal in the direct drum?

Kick Down Solenoid,
1) are the bolts tight?
2) pull the plug to make sure its not being energized when driving. This could lock you out of third gear if the switch is loose, missing a steel gasket(early unit) or being fed 12v and last but not least, possibly junk and stuck open

If this stuff is correct then you need to check valves in vb, and air check the direct drum with the valve body removed. The holes are on each side of the center support bolt . use a long neck rubber tipped blow gun and apply 60psi to each side .
one side should seal up and thump the clutches and the other side will blow back out other hole until you plug it up, then listen for the thump of the clutches, and for leaks.

Did you use 4 steel sealing rings or 4 teflon?? ... Steel ones can busticate if your not careful. best to always double check when working the drum into the int clutches by installing it twice to make sure.

Problems suck, but that is why were here to help and to learn.
Good luck to you.

 

On second thought,
What does "milled the 1-2 piston and plugged the hole"" mean??
What hole did you plug???

 

The one two shi ft piston and the bleed hole for it. To over ride the fail safe so icq. Hold 1st gear longer. As for the kick down 12v was never attached to it to start with so I didn't plug it back in.

The 2-3 piston I only removed the spring and block the feed port to it.

I got 12in of vac I checked that the first time before pulling the v b and putting all the check balls back in. There I only had two to start

 

We need to clear up terminology on the parts.

The valve body has shift valves inside it , not pistons. Where did you find this information for the modifications you performed on the valve body? If you did some grinding on the 1-2 shift valve, and did not deburr the valve, it may be stuck.

12 inches of vacuum is a bit low when measured at the modulator

 

Every thing was cleaned up on the 1-2 valve and it moves free in the v/b . the mods I fond them on a few deff utube videos, as well as a fourm called yellow bullet, and Herr as well.

There was two deff sep plats I fond with where to drill holes. I drilled the holes for the one thay I thought was mine. I used this items to drill my holes

 

That thing should not be shifting at all under acceleration with only 12 in of vacuum.You should have a min.of 17 for it to operate properly.From what I can read from the mods that you did,they were done right....A simple test would be for you to get a hold of a hand vacuum pump with the gauge in it. Hook a long hose from the pump to the modulator (plug the line going to the motor)and hold the pump in your hand while you are in the car .Pump it up to 17 in lbs. and drive the car.See what happens.That test will either confirm or eliminate that that is the problem.

 

I should have seen that coming. I meant 12 inches under a load.

""The 2-3 piston I only removed the spring and block the feed port to it"".
If i didn't think you are referring to the accumulator piston in the valve body,
I would consider this sentence to hold major clues to your problem.
Nouns and adjectives would really help us here.

Question,
What gear are you missing?
From your first sentence, You said,
""So I rebuild my th400 bc it would only shift once. It's still.doing it.""

From what i am reading, the problem was there before you did anything to it.
So its what you "didn't do" is what we need to find out.
Question,s
Did you find burnt clutches ? and if you did, did you change the rubber seals in the drum or seals on the pistons? and if so, how did you get the pistons back in?
Did you miss the center lip seal in the direct drum, or put it on the drum upside down.?

Lots of good advice here.
Start with Ricks advice and hand pump 17 inches directly into the modulator and drive it. Make sure you recheck your fluid level before driving.
Even if it still does not shift, leave the pump on it till you figure out your vacuum issue.

 

Is hard to drive it when technically its not legal to drive on the road. I can get away with short trips down the street and back but that's about it. It's an adjustable mob where should it be set for a "factory setting

 

Here was happened last pass down the track I heard a pop on the top end. "Pcv valve hit the hood do to bad valve guilds in heads." At the ticket booth I stopped and got my time slip and it wouldn't move. I put in 1 st gear and it creped.

Parked it let it cool off for about an hour and it drove up onto the trailer in low. Got it back to the shop pulled the pan didn't see anything. Pulled the valve body to find piston was plastic and was cracked. Replaced it with a alum one left the spring out and plunged the port to it. New seal o. The new piston. Why I was in there I drilled the holes using this pic . bast off what I seen on the sep plate. Milled the 1-2 valve and plunged the hole in the VB with a check ball. Put it all back together. With new gaskets
Did the shift only one time even if I shift it like it missing 2nd gear. So I pulled it apart replaced all lip seals and used a lip seal tool to do it . not Burt clutches or steels but I replaced them BC I had new ones in the kit. I let them set in aft over night. Put it all back geathe and still the same issue. I put all the check ball back in after running a two check ball system and still the same thing. If I shift form 1-2 nothing and I out it in drive like I'm shifting to 3 it shifts about 4500 and drops to 2500

 

OK, So you are missing second after grinding and plugging up stuff.

Were you missing second gear "Before" you touched it ????

 

I fixed it dont really know what did it I flushed the system, and I used a hand pump like i I was told and I have all three gears I'm taking it I wasn't getting the right vac down there so not shear what did it but with the hand pump it shifts fine

 

Can you show us what you did to the the 1-2 shift valve?
I'm guessing this is where your problem started.

Question, Did you take a good look at the intermediate sprag?
Does it spin both ways??

 

All I did to the 1-2 valve was mill the big end on two sides. U can buy them like this but I did it myself. Not the sprang does not spin both ways it spins one way but not the other.

Again I fixed the port I was using did not carry the right vacuum. BC I plugged the line back in and it acted the same way . but when I tapped into the a vacuum line as my brake booster runs off ,it shifts just fine.

 

Vacuum Sucks!