[upstand2]

Well after rebuilding my first transmission I've found that it works pretty good other than I only have reverse on jackstands. I cannot even feel the trans drop into reverse. P, N , L1, L2 and L3 are fine. I have engine braking. I've drove around a bit hoping that it was a checkball that needed some petroleum jelly melted. The troublshooting section of my Motorbooks Workshop TH400 book implies that the forward clutch is bound up. The funny thing is that a transmission tech set this up for me with 6 Blue Plate frictions and Kolen steels. Just looking for some opinions before I get the joy of taking it out again.

 

[Crosley]

pull the valve body down and air check stuff, before trans removal.

this requires compressed air of some type , rubber tipped air gun

you can air check the direct clutch , rear band , 2nd gear clutches easily.

You can look at check ball locations too.

 

[upstand2]

Well, I dropped the pan, filter and VB after maybe 4 miles. I found the pan already had a coating of gray sludge and glitter. This doesn't seem right to me, but I'll try your recommendations Crosely, because I think the damage has been done. Might as well continue learning.

 

[upstand2]

I should have mentioned this before but this Trans has a transgo stage 3 kit in it from a trans that I cracked the case on.. Over the weekend I shimed the reverse and intermediate servo as it says in the transgo instructions. Trango felt this was probaly it. It was'nt.
I then pulled the trans and swapped in another forward drum assembly. That wasn't it.
But I did just notice something. My rear servo had two springs, a large one that transgo says nothing about , but do show in the instructions and a smaller one that they say to discard. The strange thing is that in Jakeshoes link to the Army tech. manual , the Army rebuild pic of the rear servo DOES NOT SHOW THIS LARGE SPRING. Maybe it's to much pressure?
Also, I read somwhere that Blue 4l80E frictions(like I have) need a 4L80e backing plate.Maybe this is where the glitter came from.
Anyway , this is where I am in my TH400 study. Learning (alot) from my mistakes.
Next weekend I may try swapping a front pump and converter that is known to be good.

 

[jakeshoe]

OK,
Before you "throw parts at it" take a diagnostic approach.

First,
A bind up in the forward clutch drum will cause a no reverse condition BUT at the same time you will have forward drive in neutral, as if in 1st gear.
Reverse will act like a transbrake, the engine will load against the stall converter, the vehicle may engage reverse and drive through the welded together or too tight forward clutches.

You need several things for reverse to function.
First you need pressure.
You have this if it drives fine in forward gears. Don't mess with the pump or converter, they are proven good if you have forward gears.

Second you need drive from the engine. You have this, the converter is working in forward gears, so it's fine in reverse as well.

Now,
you have two major elements that need to hold for reverse internally.
The Low/Reverse band and the Direct (3rd) gear clutches.

As Crosley stated, an air check on both of these is easy.

Check both sides of the center support bolt. One will hold, the other will leak out the opposite hole but also apply the clutches.

Go ahead and check the center support bolt itself, this is 2nd gear.

Now the hole at the rear of the case goes into the servo. Air check it but put a rag over the servo area, because you are going to get lots of ATF from the backside of the servo.

If all air checks good, you may have a too short servo pin. This has become an issue on the TH400's and 4L80E's in recent years IMO.
Band diameters must not be held to the tolerances they used to. Band clearance must be closely checked on the TH400 and 4L80E.
Take a good OEm band out, install a new OEM band, and put it together and in some cases the damn thing won't have reverse.
The only plausible explanation is the band diameter or overall length has changed.

If you have 3rd gear, look at the band and servo area closely.

90% chance this one can be fixed in the car...

 

[Dogbreath077]

Excellent reply Jakeshoe, that's the way to approach a problem, logically.

 

[upstand2]

Thank you ,Jakeshoe and everyone else for putting up with me. I'm just starting to understand what goes on inside the transmission.

"A bind up in the forward clutch drum will cause a no reverse condition BUT at the same time you will have forward drive in neutral, as if in 1st gear."
**Yes, thats what was happening with my rebuilt forward assembly. With the old core forward ,it does'nt happen(drive in N) but first only works for about 5 seconds once I put it in gear.

"If you have 3rd gear, look at the band and servo area closely"
** third gear did slip once while trying to accelerate in third.1st and 2nd did not slip. I even turned 28" drag radials over on the line lock to see what the converter flashed to.

 

[upstand2]

I forgot the large snap ring for the backing plate on the Direct Clutch.