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400 turbo

Posted: Sun Apr 08, 2018 9:14 pm
by vht
What would you need to update on a 400 to say handle 700 HP, strip use with slicks and no transbrake? I know they recommend the 4L80 type direct drum with a 34 element sprag. I've researched some but seems like there is a whole bunch of opinions. It'll be converted to manual VB.

Re: 400 turbo

Posted: Tue Apr 17, 2018 6:38 am
by Coloradoracer
Just pay attention to clearances and you'll be set. 36 element sprag is the only thing I'd worry about. A stock th400 can handle WAY more hp than you might think. Stock frictions and steels will also be fine. Might want to restrict the converter feed though, and perform the dual feed mod for the high clutch drum as well, but they are easy to do. A quick search on here should find you the information on those, it's been discussed here before.

Still my fav auto trans. Easy to work on and brutally strong!

Re: 400 turbo

Posted: Tue Apr 17, 2018 8:25 pm
by af2
Ron Sessions book is second to none on the 400. Very good illustration. I wish I had it when I built my first one.

I run a manual Valve body and leave at 6800 on the brake. Stock parts with good clutches and the 32 sprag has been good. Set the clutches to .050" and have fun.

Posted: Thu Apr 19, 2018 6:43 pm
by dwilliams
Keep the stacks at minimum height. Sessions preferred paper clutches over the molded ones when he wrote the books; I've always followed his recommendation and stayed with paper, and never had any reason to regret it.

Re: 400 turbo

Posted: Sat Apr 21, 2018 3:25 am
by Pro Built Automatics
The TH400 as said is a very strong transmission to start with. Here are some tips. Always use the 34 element sprag. Use the TransGo Performance Shift kit or equivalent, use the Borg Warner Hi-Energy 4L80E clutches in 2nd & 3rd gears. BW oem stock clutches in the forward clutch pack. Peek sealing rings on the pump and center support, cast iron rings or Viton rings on the accumulators and band apply servos. Always use the TransGo intermediate clutch snap ring or the TF727 (PN22878C) snap ring here. This is to stop the lugs from breaking out of the case. Install the 2004R low/reverse cup seals PN54386A on each side of the center support bolt to seal the case to center support. This works very well, to stop the leakage between the case and support. Make sure you check the main shaft for a restrictor in the back end of the shaft, if there is one knock it out, as this limits lube to the rear. Use the plastic thrust washers where applicable. If you are going over 6,500 rpm use the TransGo springs from their kit in the direct drum, or make sure you drill a .035" - .040" hole just underneath the piston at the outside area in the corner of the drum to act as a bleed for oil trying to make the piston apply (at high rpm 6,500 rpm or more) in the top of First gear. Do not remove the rubber in between seal in the direct drum, as this aggravates 3rd gear clutch release. You can leave off the 2nd sealing ring on the center support if you want when using the dual direct feed setup from TransGo or equivalent. On the filter inlet tube, always install two O-rings. Use the late (1999 & up) extra wide 4L80E Raybestos Hi-Energy intermediate band and the BW 4L80E low/reverse band if the oem band is worn out. Always use the vacuum modulator as this will keep the pump alive. .060" - .080" direct clutch clearance. Leave in the waved steel in the forward clutch pack. Use Dexron type oils only, synthetic or non-synthetic.

Re: 400 turbo

Posted: Sat Apr 21, 2018 11:42 am
by mike hohnstein
Do not remove the rubber in between seal in the direct drum, as this aggravates 3rd gear clutch release.

Please expand on this comment. Did Gill tell you that was the thing to do??

Re: 400 turbo

Posted: Sat Apr 21, 2018 4:15 pm
by Pro Built Automatics
If you are talking about Gil Younger, he mentioned it. There are two drain holes in the drum and when removing the in between seal, you are forcing the oil to the outside of the drum from centrifugal force (on the 3-2 downshift). You are now using the smaller of the two drain holes only, (the inner drain hole is larger) and you are slowing down the release of the clutches because of this. Leaving in the seal forces oil out of both drain holes for a quicker release.

Posted: Mon Apr 23, 2018 6:17 pm
by dwilliams
Ah, that makes sense.

Re: 400 turbo

Posted: Sun Apr 29, 2018 10:15 am
by mike hohnstein
Might make sense, but as in many of Gil's 'theories' doesn't quite work out in the real world.
OP needs a full manual valve body with 1/16" bleed hole drilled in the back of the direct drum just inside the large seal bore.

Re: 400 turbo

Posted: Sun Apr 29, 2018 11:37 am
by Alan Roehrich
It makes sense, if you're downshifting from 3rd to 2nd under power on a regular basis. In a drag car, or even a street car that doesn't do that, I remove the seal.

Re: 400 turbo

Posted: Sun Apr 29, 2018 6:56 pm
by af2
Alan Roehrich wrote:
Sun Apr 29, 2018 11:37 am
It makes sense, if you're downshifting from 3rd to 2nd under power on a regular basis. In a drag car, or even a street car that doesn't do that, I remove the seal.
Every one!!

Re: 400 turbo

Posted: Mon Apr 30, 2018 5:23 am
by Pro Built Automatics
I agree. I rarely build drag race only stuff, by far mostly Heavy Duty, street racing and some drag strip.