[428GTO70]

I am working on getting my TH400 back together and have a couple questions.

I have done these internal mods so far:

1. Internal dual feed mod of removing the direct drum inner seal, the second seal from the center support and plugged the reverse feed hole in the case with a cup plug.

2. I have removed the spring from the 2-3 accumulator and plugged the feed hole with a set screw.

3. And I have also restricted the converter feed hole in the pump with a drilled set screw to help keep the engine thrust bearing healthy.

I recieved a basic Transgo shift kit along with my trans rebuild kit that includes a new valve body seperator plate, gaskets and a few springs for the valve body, governor and modulator.

I believe this transgo shift kit is designed to dual feed the direct drum in a different way as well so I was wondering if I should be using this kit at all since I already took care of that?

Should I just reuse and drill my factory divider plate and maybe just use the springs in the kit to boost the pump pressure and such? or should I just not use the kit at all with the mods I have already done?

I have a baby blue spring in my pump now and the one in the Transgo kit is yellow if that matters at all. This is for a street driven car that I want to shift somewhat firmly but not overly harsh.

Any help would be appreciated, looking for durability behind the 550ish HP my engine should come close to but I still want the car to drive comfortably on the street.

Thanks in advance!

Bob

[Half-Inch Stud]

Since you did item 1. Then you can use the factory separator plate.

Use the Yellow pump spring because it is more firm than the baby blue, for a little high Line Pressure.

i flip the puck & remove the Spring in the VALVEBODY 2-3 Accum, for good results.

Last detail would be checkballs. Only use 3-4 checkballs: those along the center line of the Case. Leave-out the checkballs near the 2-3 accum. I do not plug/block the 2-3 accum.

i use a super-firm Yellow Spring in the 1-2 Accululator, instead of the blue 1-2 accum spring. I bough a box of them so have many extras; PM if want. HIS

[428GTO70]

Originally Posted by Half-Inch Stud

i use a super-firm Yellow Spring in the 1-2 Accululator, instead of the blue 1-2 accum spring. I bough a box of them so have many extras; PM if want. HIS

Well, here is something strange. My trans doesn't have a spring on the 1-2 accumulator valve in the valve body and its that way from the factory according to my Mitchell manual. In the exploded view picture it shows a view with and without a spring, and my trans code of PX is the box view without a spring. Is this a bad thing?

[Cliff R]

+2 on using the stock separator plate. Be conservative with the feed hole sizes, especially if you increase line pressure.

Jake outlines the dual feed on his website, see the link below.

I'd leave the 1-2 accumulator alone if you are using the upgraded 4L80E 4 clutch pack with flat frictions. A little "cushion" there is fine. You can firm things up a bit more if using the factory type smooth/waved frictions.

Transgo provides an accumulator valve tuning chart with their better kit. The factory had all sorts of different deals going on there. In most cases I leave all that alone for initial testing, and to date have never had to go back in and make any changes in that area.

I would also modify the shift valve and block the exhaust hole in the VB to provide full manual control of the 1-2 shift.

http://www.jakesperformance.com/TH400_Rebuild_Tech.html

.....Cliff

[Half-Inch Stud]

Originally Posted by 428GTO70

Well, here is something strange. My trans doesn't have a spring on the 1-2 accumulator valve in the valve body and its that way from the factory according to my Mitchell manual. In the exploded view picture it shows a view with and without a spring, and my trans code of PX is the box view without a spring. Is this a bad thing?

Would you believe I mean the REAR SERVO?

[428GTO70]

Well turns out the Transgo kit I have is just a basic shift kit, I dont believe it actually dual feeds on its own. Would it hurt anything to install this kit in full along with the mods I have already done? Not sure if they are fully compatible? I had already installed the yellow pressure spring from the kit but that is it so far. Should I toss in the few other springs with the kit and the seperator plate? Or should I leave well enough alone...and if so should I remove the yellow spring and go back to the stock blue one? Is dual feeding a good enough mod to hold the added power or is the added pressure of a stiffer spring going to help out here. Sorry for rambling on about this but I just want to button this thing up already. From what I have read the Transgo shift kit is decent I just dont know if its going to perform correctly with the dual feed mod and 2-3 accumulator disabled. Im probably over thinking this a bit.

Also, HIS...what does the super stiff Yellow spring accomplish?

[Half-Inch Stud]

Originally Posted by 428GTO70

Well turns out the Transgo kit I have is just a basic shift kit, I dont believe it actually dual feeds on its own. Would it hurt anything to install this kit in full along with the mods I have already done?.....

Also, HIS...what does the super stiff Yellow spring accomplish?

Q1: stick to my prior posts, and CLIFF's advice on hole re-sizing in the GM Separator plate.

Q2:rear Servo Spring; I don't know for sure. Probably firmer 1-2 without being nasty, same with Reverse apply, and quicker Rear band release on Reverse & Manual 1st. Some experts say it's moot. I say it's an improvement & is part of my recipe for a responsive Street/Strip TH400.

[Cliff R]

I'd set it up to dual feed and stock separator plate. A stock TH400 rebuild kit should have the smooth/waved intermediate frictions in it, not the flat ones. Do the full control 1-2 shift mod as well, or the unit will upshift to 2nd even if the selector is left in the L1 position.

When following recomendations for shift improvements/performance, keep in mind everyone has their own little deal going on here, from line pressure to plate hole size to clutch pack set-ups, etc.

Unless you are following every single detail from someone elses build specs, the results will not be exactly the same anyhow......Cliff

[428GTO70]

Yes, I am running stock rebuild Raybestos waved intermediates with 3 frictions and they have about .060 movement when I air tested them. The 2 drums have around .050 clutch clearance on both with 5 clutches each.

I will contemplate the 1-2 manual mod although I usually just leave the car in D. Not sure I have a huge need for it, although ive never had 500+ hp before either so a little more manual control could be fun . Im assuming the safety "auto upshift" into second while shifted into 1 probably happens at the same RPM it would on a wot launch in D, and this would be regulated by the Governor as it is now correct? I probably dont have the best shifter to be messing with manual shifting, I have a factory 68 His and Hers and it does NOT have very positive stops built into it.

Im guessing I wouldn't want to shoot past D into N while trying to bang through the gears too many times, although Im sure I would be careful.

Thanks for the info guys, I do appreciate it. It's kind of fun working on this transmission BTW. Not as difficult as I thought it may have been.

[Cliff R]

Most TH400's shift out of 1st pretty early left in "D" at full throttle without governor and VB modifications, at least from what I've seen here. The full manual modification will not effect this, but it will allow you to run low gear to whatever shift point you want. It's a good modification, but be aware that if you are going 120mph and put the selector in low, it's going to shift to low gear!......Cliff

[428GTO70]

Ok you talked me into it, Ill just be carefull with it. I ground the flats on the shift valve and went and got a 1/4-28 set screw from the hardware store and plugged that exhaust port. Easy enough, and I believe I'm done with the mods.

Im thinking I can get the trans off its tail and back on the bench and get the VB guts back into place now.