TH400 problems

Discussion in 'The "Juice Box"' started by partsrparts, Jul 14, 2021.

  1. partsrparts

    partsrparts Silver Level contributor

    I have a 1968 TH400 behind a 350sbb in a 76 Skylark. This trans was supposedly rebuilt about 10,000mi ago, It was also "supposed" to have a shift kit in it. Anyway when I had it at the track a few months back it was hitting the shift light in 1st and 2nd and once in 3rd in a 1/8mi. i'm running 3;23 gears and would barely be hitting 3rd in a 1/4mi. (6,000rpm). My new helmet has real thick padding and I'm hard of hearing so I heard nothing. Seems to me to be a bad trans slip. Since then I've had it on the street and in 1st gear at about 5,300rpm it makes a loud like metal on metal noise.
    Today a friend of mine rode with me and I foot braked it to check the stall and it went to 3200-3300rpm, it's one of JW's converters, it flashes to about 3400.
    I left it in 1st and took it up and about 5,300 it started the noise, held it there and checked all the gauges and they looked good.
    Did it again a 2nd time and the car seemed to lunge a little and under a steady throttle it felt like the brakes were being applied.
    After doing this twice for a total of 30sec. combined the trans temp was at 210 and it usually takes going up in elev. on a hot day to do for it to get that high. I drove it for maybe a half mile, it came down about 5deg but started going back up just idling.
    Is it front pump?, converter? I read something about maybe a twisted pump stator tube.
    Running synthetic trans oil, never been above 210, oil alittle darker.

    Keith
     
  2. TrunkMonkey

    TrunkMonkey Well-Known Member

    Pull the pan and look for suspended metal and settled material, and color of fluid.

    Post your findings.

    You may have rolled the sprag/roller clutch.

    Or possibly the converter.

    Anytime you have internal transmission issues, stop driving and pull the pan, you cannot fix any problem by running it.

    Replacing soft parts is much cheaper that hard parts, and it does not take long to destroy the expensive parts.
     
  3. partsrparts

    partsrparts Silver Level contributor

    Fluid maybe a little darker, looks like some silver suspended in the fluid, hard to explain how it looks. I will try to get a pic. some black sludge like substance in the bottom of the pan, not a lot, but with small little metal chunks in it, like grains of sand.
     
  4. TrunkMonkey

    TrunkMonkey Well-Known Member

    Not good news.

    Metal chunks, even that small will trash bearings, bushings, the pump/stator face, gear pocket and gears, as well as planetary pinion gears and pins, clutch and steal faces, valve body spools and bores.

    At this point, you really need a post Morton on the unit, and hope to discover what is still salvageable.

    Once a pump starts loosing pressure, clutches cannot clamp and hold, and slip, generating trash that can restrict the filter impacting pressure more, but metal is indicative of component failure, and often that is a converter that goes first, and cascades.
     
  5. sean Buick 76

    sean Buick 76 Buick Nut

    Trans rebuild time
     
  6. DaWildcat

    DaWildcat Platinum Level Contributor

    Agreed on the teardown and inspection to see if it can be rebuilt or if a new core will be needed.

    No matter what, don't just throw the torque converter back into the new build without having it opened and inspected as well.

    Devon
     
    sean Buick 76 likes this.
  7. partsrparts

    partsrparts Silver Level contributor

    Just some of the stuff in the bottom of the pan. trans shit.JPG
     
  8. Bens99gtp

    Bens99gtp Well-Known Member

    That needs to come completely apart and checked well
     
  9. TrunkMonkey

    TrunkMonkey Well-Known Member

    Do not forget to flush the cooling lines. A tube cooler can be flushed. If you have a stacked plate cooler, replace it.

    You cannot get one clean enough to reuse no matter who lies to you.
     
    PGSS and DaWildcat like this.
  10. partsrparts

    partsrparts Silver Level contributor

    I will be sending the TC back to JW to get checked out. I may get a trans already built by TCI, Hughes, ect.
     
    DaWildcat and TrunkMonkey like this.
  11. partsrparts

    partsrparts Silver Level contributor

    Got the TC back from JW, looked good, just installed it into the B&M trans and in the car. Hope to get to T&T on the 27th.
     
    DaWildcat likes this.
  12. Bens99gtp

    Bens99gtp Well-Known Member

    Glad its back together
     
  13. partsrparts

    partsrparts Silver Level contributor

    Well, new trans has to be pulled and returned. If you drop the shifter into first the car won't move without a bit of throttle, fells like it's binding up like the e-brake is on, pop it up into 2nd and it releases and creeps forward. If you leave it in drive and come off a stop it acted normal at first but at the end of the drive it started to bind up. Contacted B&M and they said that it sounds like a bad valve body, they will warrenty it but they won't have any for at least 2 months.
     
  14. TrunkMonkey

    TrunkMonkey Well-Known Member

    Have whomever builds it flush the converter. If Jim had it gone through and said it's good, it got a chance to be contaminated after running it again. It does not take much to cause trouble, and hate to see you go through another rebuild and have another failure after that.

    Considering the noise you described, you likely have a lot of shrapnel throughout.
     
  15. partsrparts

    partsrparts Silver Level contributor

    The noise was in the orig. trans, had Jim check the TC, new coolant lines and flushed cooler after that. Back and forth to Jim is over $300
     
  16. sean Buick 76

    sean Buick 76 Buick Nut

    I would have b&m pay to have your converter re checked. Better safe than sorry. Tough luck man!
     
  17. TrunkMonkey

    TrunkMonkey Well-Known Member

    I misunderstood. I was thinking the transmission was still the one that had made the grinding noise.

    After re-reading your post, I get that you had installed a B&M built unit, with the converter Jim had checked, but you had trouble with shifting, and that the valve body is suspect.

    (note to self. read it again, read it again, rea...)
     
  18. Bens99gtp

    Bens99gtp Well-Known Member

    That doesn't sound like a vb issue to me.

    I'm going to leave out what happens below the actual clutches here in my explaining to try to not make this too confusing......each of the clutches once applie spins or hold something else......but we will only talk about the actual clutch to try to.keep it simplier..........try. lol

    the only difference inside the trans between manual low(M1) and drive postion 1st gear when starting out moving from a stop is in M1 the low/reverse(L/R) band is applied.......the forward clutch is applied and stays applied for all moving forward gears. Manual 2nd(M2) is the exact same a regular drive postion in 1st gear until the gear shift. 2nd gear in drive postion the intermediate clutch applies...which forces the intermediate sprag to hold the direct drum from spinning backwards...and in M2 you add the intermediate band to help hold the same drum. 3rd gear(D) the direct clutch applies which cause it to be couple to the forward clutch pressure plate which now the spin as one

    So from a dead stop if you put it in M1 and it binds, but shift to second the only change is the releasing of the large L/Rband....and the car moves.......the only way I can see it being a vb issue is if some how fluid was leaking around manual valve wanting to cross apply something

    Make makes more sense to me is if for some reason the direct clutch pack was too tight and dragging.....or they didn't have the correct combination of drum and pistons for and there wasn't a release of pressure from the check ball you would have a partial dragging apply of that direct clutch constantly........so in Reverse its ......the direct clutch.....the main drive clutch anyways and the L/R band hold the lower gear set and you go backwards as should..........you stop go to L1.......same L/R band holds....you apply forward clutch.....if the direct clutch doesn't fully release you basicly doing what a race tranny does when they apply the trans brake.....you have 2 opposite acting gears applied at once, 1st and R.....you throttle up and because its a dragging in the direct drum not a full apply you creep forward of you get high enough up.in rpms....you shift to M2 you release the L/R band from holding effectively turning off Reverse The direct drum dragging here isn't really noticed as much since it's now all spinning in the same direction inside the tranny. As you continue to up the gears the clutches are just added....they don't release. So the forward clutch being no shifting is applied in every gear going forward....the intermediate applies for 2nd....and stays applied even in Drive.....the direct clutch is just added to basiclly lock the all together and turn as one unit for 3rd...
    but if this is the chase you would maybe feel like when it does move forward you would really have a defined feel for each gear....it would feel sluggish like driving a manual trans in too high of gear


    This is assuming this isn't a full manual valve body
     
    Last edited: Aug 20, 2021
  19. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I'm sure you have a local guy who build a 400 in his sleep. Maybe it's worth it to pull it and have it inspected? It would be a shame to burn the rest of the season if it's a quick fix
     
  20. TrunkMonkey

    TrunkMonkey Well-Known Member

    @Bens99gtp Very good explanation.

    If the "bathtub" checkball is left out, it can act like a transbrake by doing what you stated. But, not an "always binding", makes me wonder if your "no checkball piston" in the direct drum the cause.

    Hate that the OP is having such a bad go with this.
     

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