TH400 trans rebuild

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

  1. Matt69olds

    Matt69olds Active Member


    Obviously, if you have too much clearance, with the thick steels, machining then piston isn’t helping. If you have too much with 5 thick steels, use 2 thin ones. Or get a thicker piston and machine it to whatever thickness will give the desired clearance. A little math is needed to calculate how much you need to add or remove.
     
  2. Luxus

    Luxus Gold Level Contributor

    Interesting. I think I'm going to get me a new thicker snap ring. It will eat up some of the extra space and it will be that much stronger because it is thicker. Thanks.
     
  3. 1969RIVI

    1969RIVI Well-Known Member

    I used the thicker snap ring that came with my transgo 1-2 kit to help tighten up the clearance a bit. Maybe throw out some feelers in the parts wanted section asking if anyone has one of those rings laying around?? I'm sure there's guys who just put the old one back in and they got one in a box somewhere?? Worth a shot!
     
  4. Matt69olds

    Matt69olds Active Member

  5. Matt69olds

    Matt69olds Active Member

  6. Luxus

    Luxus Gold Level Contributor

    Thanks for the links. I already ordered the one from tsr. The snap ring was pretty cheap, but the shipping was brutal at 4x the cost of the part. But the total was just under $20. Given I'm rebuilding it myself, I'm still coming out ahead.
     
  7. Luxus

    Luxus Gold Level Contributor

    The direct drum rebuild is done. As a sanity check, it only spins clockwise and not counter-clockwise. I also had a small hickup with it. I bought a spiral lock retaining ring but it was too big. I have to sort that out.

    I started on the forward drum. Straight forward disassembly. I found a couple things though.

    20191123_193538_resized.jpg
    This is the first piece that comes out when you take the snap ring off. Look at the groove in the face. Is that acceptable?

    20191123_193542_resized.jpg
    20191123_193547_resized.jpg
    This is the wavy plate which I would like to put back in. This is the first part I found in the trans with significant blueing. Is it still OK to use?
     
    Last edited: Nov 24, 2019
  8. 1969RIVI

    1969RIVI Well-Known Member

    That gouge to me does not look good. If it isn't too deep you may be able to machine the surface to clean it up but will have to use thicker steels to bring the tolerances back into specs. You can sand the wave plate to remove the hot spots on it to reuse it. Just make sure to sand evenly all around the plate not just the hot spots.
     
  9. Bens99gtp

    Bens99gtp Well-Known Member

    That groove is for oil to escape......I wouldn't worry about it.

    I would get a new wave plate
     
  10. 1969RIVI

    1969RIVI Well-Known Member

    I just learned something new! See Ben this is why you're the pro! You dont give yourself enough credit my friend.
     
  11. Bens99gtp

    Bens99gtp Well-Known Member

    No pro by a long shot. Just sharing what little other have toight me to try to help others out.

    I'm wrong alot. Just ask my wife
     
  12. 1969RIVI

    1969RIVI Well-Known Member

    According to everyone's wives we're all a bunch of always wrong idiots:D:p
     
  13. Luxus

    Luxus Gold Level Contributor

    Any suggestions where to get a wave plate? A quick search on the net wasn't very promising.
     
  14. Bens99gtp

    Bens99gtp Well-Known Member

    Stuff like that its easiest to just go getvatblocal tranny shop, they more than likely have good used ones
     
  15. Luxus

    Luxus Gold Level Contributor

    OK, but I have another option I'll try first. I've been putting it off, but I have to pull the trans that is in the car now. I'll see what the one in there looks like.
     
  16. Bens99gtp

    Bens99gtp Well-Known Member

    I wouldn't pull 2 transmissions apart at the same time......too easy to get parts mixed. Are you using the wave plate in the direct drum and forward drum? If not I think they are pretty much the same thickness......I know the steels are different thickness but i interchange them all the time.

    The forward clutch isn't a shifting clutch, keeping the wave plate in cushions the feel of going into gear from park to drive.

    Keeping the wave plate in the direct.....2nd clutch down, helps keep a to harsh apply into reverse.......there is more line pressure in reverse.......but keeping it in also softens the 2-3 shift.

    I dont normally put either wave plate in but mine is a racecar with alot of rpm stall which also soaks up gear apply.
     
  17. Matt69olds

    Matt69olds Active Member

    I have seen lots of those forward clutch hubs with that groove, I assumed it was a manufacturing procedure. I couldn’t think of anything that would cut a groove like that, and having many parts with the same groove made me think it was supposed to be there. I had no idea what the purpose would have been, but an escape path for fluid makes sense.


    I omit the wave plates, especially the later model beveled springs. I have seen many of those break, and the pieces wedge themselves under the steel plates, preventing the clutch from fully releasing. I personally can’t tell a difference with or without the wave plate as far as engagement. Besides, only a girlie-man would be opposed to a drive engagement with a little authority!!
     
  18. Luxus

    Luxus Gold Level Contributor

    Well I decided to use all the wave plates because the car will NOT be a drag car. The trans needs to be stronger for more power but I'm not concerned about losing a few tenths because I did not tweak everything I could. It needs to be strong, but also comfortable. Worst case scenario I'm also going conservative with the valve body. I can tweak it later if I'm not happy with the trans performance.
     
  19. Bens99gtp

    Bens99gtp Well-Known Member

    We are not talking the different in shifts with or without wave plates being tenths, we are talking thousandths.

    To me from what I understand the issue with the wave plate is exactly what you see with yours.......with higher rpm, higher hp motors when the clutch starts to engage you only have those few high spots starting to engage and it slips them and starts the burning process. Once burning starts on that friction material that's it, it looses grib.....and it's the accumulation effect of shifts over and over wearing out a clutch.

    I'm confused as to why your forward clutch did this since it's a now shifting clutch
     
  20. Bens99gtp

    Bens99gtp Well-Known Member

    I was told by profession rebuilder thats what the grooves are for.....now if that's true or not no clue. The way i was told was that it is possable if the fluid between the plates cant escape on apply a clutch could slip or be slow to engage due to the fact that fluid is not compressible. And since when clutch applies the friction plates and steel get squeezed against the reaction plate fluid movement is going towards that plate so the groove is cut to give the fluid a chance to exit.

    I always question this fluid movement from the piston statement seeing it moved less than .100.........as I've gotten older and know a touch more I bet it has more to do with centrifugal force causing an apply.

    The fluid being trapped in the spinning when not applied, could swing to the outside and force a false pressure build up.......the groove gives this fluid an escape path.

    Maybe a real expert will tell us the truth
     

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