TH400 wont hold...383SBC...

[malibu795]

heres the 383s specs...
edel rpm airgap
dart iron eagle 215cc intake 2.05/1.6vlv 64cc
4.030" bore FT with 4vlv relive total of 16cc refief volume... roughly 9.5:1
234/244 @ .050 .522/.540 with 1.6 rockers
1 5/8 headers
MSD 6AL balster SS coil
and a 600cfm carb.

the TH400 has a B&M hole shot 2400 TC
TCI #222400 steet fighet VB
TCI #228800 rebuild kit with brown clutches and forward band and pump pressure spring. 34sprag direct drum upgrade.
i can hold 1st 2nd and R no problem 3rd will slip about or just before 1/2 throttle
i have done line pressure tests these are the results.
@1000 with modulator disconnected.
R is 180psi
3 is 120
2 is 150
1 is 180

2000rpm
1st 210
2nd 200
3rd 130

1000rpm in P/N is 160psi
this test was done wednesday.. i pull the transmission went through double checked, lip seals, teflon seals, and all passages in the case and intermediate support.. all checked out between yesterday(thru) and today(fri)
i havent had the chance to check line pressure currently....
1-2 shift is pronouced but not hard.
2-3 is soft and barely firm...

now im some what speculating here...

TH400 transmission. Boost valve wear results in oil leaks and poor line rise. This “Factory style” reverse boost valve and sleeve is manufactured from hardened steel to prevent wear. Vehicles with a TH400 transmission frequently have poor line rise, soft 2-3 shifts, and/or reverse engagement difficulties. These problems can be caused by the reciprocating reverse boost valve wearing the inside diameter of the boost sleeve. When this occurs, oil that enters the modulated throttle valve orifice leaks past the boost valve and exhausts through the reverse orifice or to the sump, resulting in poor line rise. Also, reverse oil can exhaust both to the sump and back through the modulated TV orifice. The outside diameter of the boost sleeve also allows some leakage through the pump body, which can increase boost oil loss.

i have been told by several company that brown clutches "should" have no problem hold the said 383.....

part of me says go full manual VB.. other part say through red altos in... the red clutches wont fix the ~70-80psi line pressure drop when 3rd gear is engaged

any help???

 

[Anonymous]

sounds to me like there might be too much slack in the direct clutch pack... did you try shimming it tighter by taking out the wave washer and adding another steele instead??? i dont know much about th400's, but thats what we do to pg's and 350's... i always set them up way tighter than the book says too... just a suggestion...

 

[malibu795]

theres no wave plate in the direct clutch.. and not enough room for an extra steel.. acordign to ATSG some have them some dont...

i "function check" if you will the direct clutch with 150psi shop air with the clutch pack installed.. work smoothly.

one of the things i would liek to knwo is why is the line pressure droping from ~200 to 130psi @ 2000rpm

clutch pack starts slipign abotu 2900-3000rpm while driving

 

[Anonymous]

maybe you have a compromised seal in the center of the piston and under load it leaks????????? like i said, i dont know much about them 400's, but i would tear it down and look really close at all the piston seals and the reverse pack too... before you smoke up a set of clutches and steeles. good luck man, you just figured out why i run a glide.. only like 1 real moving part in them

 

[malibu795]

there are 3 cltuch packs
forward (on for all three gears forward)
+ intermediate gives you 2nd gear
+ direct cltuch gives you 3rd
rear band+ direct clutch= reverse

 

[Anonymous]

check the reverse.

 

[bbc_cutty]

i have kevlar clutches in my t400 with a 3000 stall, and a FMVB and i beat it like a dirty wh*re, and have never had any issues, its beat on buy a built BBC, and its going to be pushing my new combo,

11.5.1 496, aluminum head, forged egale rotating *ss. motor, hopfully 700hp NA plus a 250 hit.


my only downfall is the B&M stall....need an anti-ballon converter.

 

[8secChevy]

I had the same problem a while back. Good 1-2 shift but slow & soft 2-3 under load. It had good line pressure at idle. It ended up that a checkball was not reinstalled in the valvebody ( It is a full manual ATI ) so pressure would bleed off and cause the soft shift. Not saying this is your problem, but somtimes its the dumbest little things that get overlooked. ](*,)