TH400 trans rebuild

Discussion in 'The "Juice Box"' started by Luxus, Sep 26, 2019.

  1. Luxus

    Luxus Gold Level Contributor

    LOL, now you got me rethinking the wavy plate thing. :confused: Good news is I'm still in a good spot in the build to make changes if I decide to. I have read elsewhere that you should at least use a wavy plate in the forward drum or you will get a hard engagement every time you shift into gear.
     
  2. 1969RIVI

    1969RIVI Well-Known Member

    I think you're right on that one I do recall reusing one wavy plate and discarding another in my buildo_O
     
  3. Luxus

    Luxus Gold Level Contributor

    So an update on where I'm at. I finally got my thicker snap ring for the intermediate clutch assembly. It's 0.108" and my clearance there winds up at 0.054" (staying with the wave plate). The direct drum is almost ready to go back in and it has a clearance of 0.046". I'm waiting for a new spiral lock snap ring. I am getting a new one because the one the vendor sent me one that was too big. The forward drum is ready to be rebuilt. I just have to get around to a getting a replacement wavy plate.

    So in the mean time I have disassembled the front pump and started rebuilding it. I have decided to reduce the size of the converter feed hole. I'm going to tap the existing hole, put in a set screw and drill a new smaller hole 0.150 - 0.160". With the higher pressure the trans will have, that should lessen the chance the pressure to fill the converter won't push too hard against the engine thrust bearing (or so I've been told). The pump gears look OK, but the bigger one has stains/markings on the OD. It feels OK though. Doesn't feel grooved or worn. I can post a picture later.
     
  4. 1969RIVI

    1969RIVI Well-Known Member

    Check the tolerances on the pump gears in the pump make sure they're still within spec. Put feeler gauges between the gears and the wall of the pump and between the gear cogs.Even though they look good (no gouges or chips) they could be worn down.
     
  5. BRUCE ROE

    BRUCE ROE Well-Known Member

    Engine thrust bearings can be destroyed when a converter balloons. The
    typical way to avoid that in severe service, is furnace brazing the converter.
    Bruce Roe
     
  6. Bens99gtp

    Bens99gtp Well-Known Member


    What pressure are you hoping for.......
     
  7. Luxus

    Luxus Gold Level Contributor

    I'm going to do your mods Ben, so 190 psi.
     
  8. Bens99gtp

    Bens99gtp Well-Known Member

    Be careful raising the psi too much if your using cast iron sealing rings on the center support and rear of pump.........the extra pressure forces them to rub harder.......they become like tiny saws and cut the parts.........the teflon seal help this......the 1 piece seals are best but harder to install, the scarf cut seals will work
     
  9. BRUCE ROE

    BRUCE ROE Well-Known Member

    Instead of raising the pressure, how about converting your clutch packs
    to 6 clutch discs? That is already standard in many heavy duty (500 Cad)
    transmissions, and for the direct clutch of every TH425 I have had apart.
    All you need is the thinner piston (seen on Evil Bay) and of course the
    extra clutch and steel.

    As for the wavy plate, its first small contact is not all the contact, the other
    9 clutch surfaces are full broadside at the same time. Its purpose I believe
    is to soften shifts, probably even more important if other performance
    mods are put in. Bruce Roe
     
  10. Bens99gtp

    Bens99gtp Well-Known Member

    2nd gear is the weakest gear in a 400. In over 20 ofvracibg I've never damaged a direct or forward clutch........but I'm not over 750hp.........but most of us aren't either.

    If you want more clamping force you either up the pressure or increase piston size.........you can get a center support with a larger piston put close to 500 pop si more clamping force on the 2nd gear clutch.

    Increasing pressure not only increasing clamping force, it speeds up the shift and makes them firmer, but can cause wear as I stated on the cast iron sealing rings and ears up hp as the motor must work harder to build the pressure.

    Normally the few basic mods listed makes 2nd gear strong enough and ppl are happy with the shift feel.
     
  11. Luxus

    Luxus Gold Level Contributor

  12. Bens99gtp

    Bens99gtp Well-Known Member

    I've never heard of adjusting the other 2 plays other than front and rear, but makes sense
     
  13. Luxus

    Luxus Gold Level Contributor

    OK this is probably a dumb question for you guys, but I want to be sure I understand. I know selective washers are different thickness and you are to pick the size you need to set the correct clearance. But which one is the selective? Is it the washer with the 4 tabs or legs?
     
  14. Bens99gtp

    Bens99gtp Well-Known Member

    At the rear like your talking it's the steel plate with 3 tabs, I like to use a roller setup here. The one fir the front half is on the pump. I have never heard of adjusting the other 2 location in that link......makes sense but I bet the parts are not easy to get ahold of
     
  15. Luxus

    Luxus Gold Level Contributor

    Yea, I'm questioning if I should do it now. The front to rear planetary play in particular is looking real hard to find something that will work. The article mentions using a selective 4 tab washer and I have not been able to find such a thing. Got to ponder it a bit.
     
  16. 1969RIVI

    1969RIVI Well-Known Member

  17. BRUCE ROE

    BRUCE ROE Well-Known Member

    I expect those 2 extra settings only come up if a trans shows a lot
    of wear, most TH400s do not. I do replace any plastic thrust
    washers with brass. Note that big 4 tang plastic thrust washer in
    the gear set. It has the same dimensions as the rotating metal
    one on the output shaft. I always replace the plastic with an extra
    output metal one. Bruce Roe
     
  18. Bens99gtp

    Bens99gtp Well-Known Member

    I need to clarify my answer better, thev3 tang steel is the case saver........the 4 tang is the selective, I use a torrington bearing in place of both of these that has small shims to set the final clearance.

    http://www.ckperformance.com/View/TRANSMISSION-CASE-THRUST-BEARING-KIT


    Now if you add or subtract anything all the way through it will effect the final outcome.
     
  19. BRUCE ROE

    BRUCE ROE Well-Known Member

    I disagree, the 4 tang thrust washer on the back of the gear set and
    rotating with it, is a fixed 60 mils thick. The one it meets in the back of
    the tail housing is the stationary selective washer with 3 outward tangs.
    Bruce Roe
     
    Last edited: Dec 7, 2019 at 8:38 AM
  20. Matt69olds

    Matt69olds Active Member

    Throw out the 3 tab spacer, get a pump bearing and shim from a later model TH350 trans. The shim is .010 thick, usually the shim and bearing gets the end play correct. You can also use pinion shims from a 12 bolt, they come in many different thickness to get the end play perfect.

    You need to drive the case bushing forward so the bearing has something to pilot on. Then replace the plastic 4 tab thrust washer in the planetary gearset with the 4 tab washer that was originally between the output shaft ring gear and the case.
     
    Last edited: Dec 7, 2019 at 8:44 PM

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