th400 simple shift kit and a few easy internal upgrades

Discussion in 'The "Juice Box"' started by Bens99gtp, Feb 20, 2019.

  1. Bens99gtp

    Bens99gtp Well-Known Member

    I have been wanting to put this out there for a little bit but never have the time to just sit down and get it done, so please be patient as this information will all get here , but I will have to do it in a few postings as I have time.

    I will preapologize, I'm having to do this all from my phone, I suffer from fat fingers and coupled with my phone thinking it knows what I'm trying to say there is likely to be some errors I didn't catch.

    This is how I do some basic mods and shift kit to th400. now before I go to far there are many different ways on how to do improvements to the the shifting and strength of this transmission. this is not the only way to do this, just how I do it and for me it works. The things I do dont make the trans manual shift only. it retains all upshifts and downshifts timing, just better. the internal changes are done to improve a few of the weakness inside the transmission.

    my vehicle is race only but retained full automatic upshift and down shifts. seeing it was race only and this is what my experience is from I cant give any information on change the timing of shifts with the govenor.

    I will break this into 2 sections, 1st will be changes that can be done with trans still in vehicle. the 2nd will require the trans to be out and tore apart somewhat to get full access to all the parts.

    please read to the end b4 starting

    I'm not a transmission shop or professional transmission builder, just couldn't afford way back when I started racing to pay to have my trans done so this is some of what I've learned to do and some tips to help that I have learned.
    Due to possible difference in clutch pack clearances and friction material, fluid pressures, factory shift valves, its impossible to nail down exactly how every transmission will shift it firmness or quickness.
    I accept no responsibility for damage to your transmission, its impossible for me to know the condition of your transmission b4 starting or how these used part that have not been fully inspected will handle the extra stresses

    If any professional builders want to chime in or correct or add to anything I have here please feel free to, my goal is to try to help improve the quality and life if your transmission. the more information we can get here the more we all can benefit.

    some of the pictures I will use are sourced from other publication, other web sites, or taken by me. I did out source some pictures just to speed up things

    section needed, valve body and case gaskets for correct year transmission there are a few slightly different one based on production year, drill bits, petroleum jelly, shop manual for parts reference

    drain fluid, drop pan, remove filter, loosen and remove valve body bolts, but leave the kick down solenoid, remove valve body. use care not to drop manual valve.
    I use a pan bolt and finger tighten it back into plate as close to center, and remove kick down solenoid, hold plate, remove pan bolt and drop separator plate ........hold plate very level or the 6 checkballs will go rolling. 2nd gear servo piston will most likely come down as well. see picture 1 of order of 2nd gear servo if needed. just get the parts in order and set aside the servo for now.

    carefully clean any old gasket material from valve body, separator plate, and case......use care not to gouge anything especially the case.

    1st..........carefully clamp down the accumulator in the valve body in a vice, remove e clip, open vice, remove spring under piston, reinstall piston and e clip. use care this spring is bigger and stronger than I first thought. see picture 2

    2nd........ remove the cover on the low/reverse servo and accumulator. there will be a lot of fluid inside. remove the larger diameter inner spring, check to make sure seal of inner piston is good feeling, if loose get a new seals. see picture 3 and 4. ck performance makes a spacer that goes under this cover, the point is to not put alot of preload to the low reverse band......this is not much benifit to street, but will reduce some parasitic loses in racing by reducing the drag the band creates.

    link to shim I use

    3rd .......... drill holes is separator plate in indicated spots. There is no correct or one size fit all size here. Everyone likes a certain firmness but some prefer more harsh than others. The bigger you go the harder it will shift. you can always take things apart and go bigger later, but you can't put the metal back once drilled.
    I have personally drilled all 4 to up to 11/64" on my race transmission but this will most likely be harsh a shift for street applications.
    If your trans doesn't have an upgraded intermediate sprag I would limit hole 1 to around .110-.125, and with upgraded sprag for street I wouldn't go over 5/32". Too harsh here can cause sprag damage. 1/8" is a fairly firm shift without being harsh.
    If you have not done the dual feed mod ( explained later on in section 2 )I would recommend .110-.125 for holes 2,3,4. if you have done the dual feed, going up to 5/32" should be a pretty firm shift. The dual feed mod requires more fluid so acts like a built in cushion.

    If you want very very firm shift all the time, and are willing to accept the risk or internal damage, drill all 4 to 11/64". see picture 5 for drill locations. take time to file any burrs left from drilling plate.

    4th.........this is completely optional, in the case there is a restriction wall, shown between the 2 painted white lines in picture 6. this wall is a restriction to the flow in the direct clutch circuit. I use a center punch, then drill vertical down to have this wall at least .190" below sealing surface. see picture 6.

    5th.........check balls, I use 3. if your transmission is in the car there is 2 ways to do this, use petroleum jelly in the locations in the case and push balls into jelly. The jelly will hold balls in place and the fluid will dissolve it quickly. the other way is to balance balls on the plate and carefully install plate with case gasket between plate and case and hold in place with single pan bolt, then start and lightly snug detent solenoid, remove pan bolt b4 installing valve body with correct gssket see pictures 7 and 8.

    6th.........install valve body. be certain to wet both case and valve body with fresh fluid b4 installing......gaskets are normally marked by cut out c or vb on the edge of gasket. vb for valve body, c for case.
    use more jelly to help hold 2nd servo into case if needed. please reference picture 1 for correct order if needed. install valve body and separator plate with gaskets in correct orientation

    torque long bolts to 6-10ft lbs, short bolts to 6-7 ft lbs, kick down solenoid to 6-10 ft lbs, be very careful on the short bolts to not strip them out.

    if you want to increase the pump output pressure you have access to the pressure spring b4 installing valve body, I dont like going much over 190 psi rated spring, if your transmission has cast iron sealing rings to much pressure can cause these to wear against the internal surfaces. simply use an extension or dowel to push up on plug, remove retainer, carefully lower down, swap spring reinstall. picture 9

    link to spring I use

    this should complete your basic shift kit with only needing minimum purchases of new gasket and filter.

    I will get my pictures together for section 2 dealing more with some easy and not expensive upgrades to the inside

    Attached Files:

    Last edited: Feb 27, 2019
    johnriv67 and 1969RIVI like this.
  2. 1969RIVI

    1969RIVI Well-Known Member

    This thread will help alot of people ben, especially the novice newbie first time trans builders like myself lol! Thank you for taking the time to get this going I look forward to reading more as you (and possibly others) add to it.
  3. Bens99gtp

    Bens99gtp Well-Known Member

    finally had time to get working on part 2 some basic modifications to make the internals stronger/better/ as effective as possable.

    1st we need to get down inside the transmission so we need to remove pump bolts, when put back together these bolts get torqued to 18-20 ft/lbs. use a small pry bar under the pressure regulator to help lift the pump up. there is 2 threaded spots on the pump for slide hammers but this has never failed me. see pic 1

    the first drum you come to is the forward clutch drum. b4 removing this I use a flat blade screw drive or scribe to make a mark on the case, this is used to help make sure all the clutches are engage properly. take the time also to bounce this drum and shaft to hear to solid sound it makes against the lower parts. just lift it 1/4-1/2 inch and you hear a very solid clunk when lightly dropping it into place. if not fully down it wont make the solid cluck sound. see pic 2

    the next drum down houses the direct clutch and intermediate sprag. mark the case the same way as b4 see pic 3. I like to remove the outer snap ring....end gap for ring is about 9 o'clock in pic 3, remove all the clutches and steel plates......keep them in order for you can grab the center of the drum assembly and lift it out. if the sun gear shaft comes up or out with it just reinstall it back down through the middle of the center support. the long splines goes down and it is alined by a missing spline but just keep spinning it till it drops back in. see pic 4 orange arch is on the sun gear shaft.

    the intermediate band just lifts out one end is secured by the pin pressed into the case, the other is apply by servo pin.

    the final friction clutch in the transmission is the intermediate and it lugs to the case. this is the weakest clutch in the transmission seeing it only has 3 clutches. remove snap ring and lift out clutches and steels. when you ut it back together make sure the ends of the snap ring in the area where the ends of the ring is supported by the case lugs. see pic 5.

    the bottom steel in all 3 clutches could be a wave plate or flat plate. swapping to a flat from wave will firm up shifts but will change clutch pack clearances. wave plates are normally a little thinner than flats, and can be easily seen by looking at them from the side. see pic 6. wave on top, flat on bottom. when assembled the wave plate if chosen to retain always goes in first against the piston. swapping these out of forward and direct packs can sometimes cause a harsher gear apply into 1st and reverse than some ppl want. so use your own decession in this matter.

    check your clutch pack clearances. I try to set the intermediate between. 040-.060, direct clutch .050-.070, and forward clutch .035-060. I use small shims placed between the top friction and thicker application plate for each clutch to find clearance. I use 4 shims place around the friction and if I can get the snap ring in fairly easy i know i have at least the thickness of the shims, if I cant then I know I have less than the shim thickness. sometimes it takes a few tries to get clearance figured out. if too much or too little clearances different thickness steels can be attained to get clearances into specs.

    1 of the first mods and most important is seeing what sprag you have in the direct drum. flip the drum over, remove the small snap ring, remove retainer and remover the outer race of the sprag. see pic 7....yours wont be black. you will have 1 of 2 sprag types. 1st is roller and is not upgradeable see right side of pic 8 or the drum will be smooth and is upgradeable to a 32 element unit. see left side of pic 8. these smooth drums came in 71 and earlier and in 4l80e. the roller is stronger than the stk 16 element on the smooth drum, but not as strong as the 32. when you reassemble this sprag assembly if using the 16 or 32 element make sure once assembled the outer race free wheels in the clockwise direction.....if not you will come to a very quick stop going into thrid gear. trust me I know from experience lol. upgrading to a gapless spiral retaining ring for the sprag is a great way to make sure the snap ring doesn't even come off on it own sometime

    the next modification is to dual feed the direct clutch piston. this can done with or without removing the direct clutch piston. if doing a full rebuild leave the inner lip seal out. see pic9. I also like to drill a 1/16" hole at the bottom corner at a 45 degree angle........this is done to help the fluid drain when released and help to prevent centrifical apply. if drilling hole the thin green line in pic 10 is the lower corner area I was was referring.

    I cant add any more pics in this post so I will continue in next

    Attached Files:

    Last edited: Nov 16, 2019
  4. Bens99gtp

    Bens99gtp Well-Known Member

    if not removing piston simple leave the second from the top sealing ring off the center support see pic 1 and 2. there are 4 of these sealing rings. the lowest can be hard to see from the top with center support in case.

    I like to do both leave this ring off and remove the inner lip seal in the direct clutch housing, but only leaving the sealing ring off will work. either way we now have a leak in the reverse circuit we need to fix. easier way to do this is to simple install a 3/8" or 11mm plug cup in the passage under the valve body as shown in picture 3. screw driver blade is over the hole in the case under the valve body that needs plugged. the 3/8" plug sits deeper down inside.....if using the 11mm make sure the cup is deep enough to be level with the case.

    from here simple reinstall the parts in the reverse order. make sure all the drums are fully seated through all the clutches. I like to reinstall the direct drum with out clutches in it, makes it easier to hold and turn when lining up through the intermediate clutches. a visual check to make sure its fully seated, see pic 4. splines all the way to the top. when I put the clutches back into the direct drum I like to use the reaction plate from the forward clutch the run down through the plates to help line them up. this will make it easier to install the forward drum. doing this work with drums and clutches is easier with the transmission vertical

    Attached Files:

    Last edited: Feb 26, 2019
    GranSportSedan likes this.
  5. Bens99gtp

    Bens99gtp Well-Known Member

    last tips I forgot to add, for the snap rings modifying a screw drive with a small notch cut out helps in removing them. especially the snap rings in the case. I used a previously broken one. I have had to redo the notch a couple times now but you get the idea. leave a little ledge that gets under the snap ring to help you if it out.

    if your going to replace the lip seals on the pistons you will need to get a piston installing sleeves to make the job alot easier. I bought mine years and years ago. they were under 50 bucks then. you can use other types but I've only ever used these. I've heard piano wire formed into a small loop helps push the lip seals in

    Attached Files:


    BRUCE ROE Well-Known Member

    Thanks for the pictures. Getting those clutch packs properly seated is about
    the hardest part of the job for me. I measure from the front to be sure they
    are all the way in. Bruce Roe

    Attached Files:

  7. Matt69olds

    Matt69olds Well-Known Member

    Is that a typo? You drill the spacer plate to 11/32? I would think that would knock the dash out of the car! I have never tried holes that big

  8. Bens99gtp

    Bens99gtp Well-Known Member

    yes typo on the last size I will correct it. 11/64 is the biggest I have run but as I stated it's a very harsh shift. the trans I ran them in was race only. It personaly felt it to be ok on the track.......not sure how it would be on the street. if you dua feed the direct drum piston as described later, this acts like cushion in the 3rd gear shift..... the dual feed puts fluid to the entire surface area of the piston for more force once fully applied, but since there is now almost twice the surface area to fill we need to fill it faster to not have a slide shift feeling.

    going to full 11/64 in hole 1 I for sure wouldnt do without an intermediate sprag upgrade.

    most ppl are very happy with the holes between 1/8" and 5/32" which is where the 32 came from. i dont think you go to 11/32 and not get into other circuits on the plate honestly good catch there matt.

    that's the problem with proof reading your own always know what you ment to say and skim over simple errors
    Last edited: Feb 27, 2019
  9. 1969RIVI

    1969RIVI Well-Known Member

    Ben do you have any pics of the other side of the drum where that 1/16" hole comes out? When all the clutch packs are in the case what is the measurement from top of the drum to the bolt flage of the pump, I can't read the ruler in that pic accurately?
  10. Bens99gtp

    Bens99gtp Well-Known Member

    I dont have any pics of that hole, I just run through at close to 45*, go slow to not break the but off, the drum drills surprising easy. This is done to help prevent centrifical apply in upper rpms and help transbrake release. It's not a mandatory thing to do.......and if hot dual feeding I wouldnt do it.

    Bruce put that pic up I dont measure that, I just scribe the inside of the case b4 disassemble.
  11. 1969RIVI

    1969RIVI Well-Known Member

    As for the 3/8" cup plugs can they be aluminum? I couldn't find any locally anywhere until I went to a trans shop down the road and in his misc. Parts (junk) bin he found 2 aluminum 3/8" cup plugs.

    Attached Files:

  12. Bens99gtp

    Bens99gtp Well-Known Member

    Dont see why not, the 3/8 fits farther down in the hole, the 11mm fits up flusher
  13. 1969RIVI

    1969RIVI Well-Known Member

    Ok great thank you!
  14. Matt69olds

    Matt69olds Well-Known Member

    If you measure in .410 from the outer edge of the drum that will put the hole just inside of the piston seal.
  15. 1969RIVI

    1969RIVI Well-Known Member

    Here's where I drilled it on the inside and where it came out on the outside.

    Attached Files:

  16. Bens99gtp

    Bens99gtp Well-Known Member

    Looks just fine, dont forget to debur the seal side to be safe
  17. 1969RIVI

    1969RIVI Well-Known Member

    I'm going to deburr both sides with a scotch brite pad.
  18. 1969RIVI

    1969RIVI Well-Known Member

    What are the pump half bolts torque specs 20ft/lb same as pump to case bolts?
  19. Bens99gtp

    Bens99gtp Well-Known Member

    I'm pretty sure the half go to 200 inch pounds and 20 for the pump to case
  20. johnriv67

    johnriv67 Well-Known Member

    Hey Ben I'm confused on what the 3rd and 4th drilled holes are for in the first part of your description and picture.

    I know or at least think that Hole 1 is for the 1-2 firmness and speed and Hole 2 is for 2-3 firmness and speed. What are Hole 3 and 4 for?

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