TH400 setup woes

Discussion in 'Transmission & Driveline Topics' started by Lee45, Dec 11, 2017.

  1. Lee45

    Lee45 Member

    59
    5
    May 28, 2017
    Really need some help setting up my th400. Cam is on the rather large side, 246@.050, and I have 4.56's with 28 inch tires. I'm lost on how to adjust the modulator, whether I need the electric kick down, and what to do with the governor. First, reverse, second, and third all work perfectly and are very firm. But it shifts out of first pretty quick and takes longer to go to third. Also has to pretty much completely stop to go back to first. Trans does also have a transgo pro 400 kit but doesn't hold first to high rpms. Set the governor up with springs from the kit towards the middle of the spectrum. Lurches extremely hard into first reverse aswell. Also any concern, it has a hays 4200 stall.

    Makes me wanna put the 4 speed back in....
     
  2. camaro71/holland

    camaro71/holland Veteran Member

    968
    29
    Aug 27, 2003
    The Netherlands
    With 4.56 it isn't too strange to go through first gear like a rocket...

    Hard gear application into reverse is normal due to higher line pressure. First should be less unless you have fixed line pressure in all gears, or have enlarged the openings in the spacer plate.
     
  3. 1978 Z/28

    1978 Z/28 Member Gold Member

    35
    8
    Jul 17, 2017
    New Brunswick
    I have 1978 Z/28 with a turbo 400, 3500 rpm stall speed converter, 4.56s and a strong engine. It would shift out of 1st gear in my 75 foot long driveway at under 5 mph and would not downshift till stopped. Shifted great manually. Asked shop that rebuilt about this, Mark said not to worry. Because of my setup, transmission did not have to stay in 1st gear long. Raced car ran 13.0s at 108 mph on street tires 1980s and drove on street for 10 years with no problems

    David
     
  4. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    9,362
    238
    Nov 4, 2004
    Ringgold, GA
    My TH350 with 4K stall converter would be in 2nd before it got through a street intersection.
     
  5. RS1979

    RS1979 Veteran Member Lifetime Gold Member

    2,910
    367
    Jun 18, 2013
    Memphis, TN
    I have the same problem. I manually shift mine now. I drove with a manual valve body for years and got used to it.
     
  6. Lee45

    Lee45 Member

    59
    5
    May 28, 2017
    Thanks for all the replies. Actually got it to shift pretty half decent. Any ideas as to why it doesn't stay in first?
     
  7. Lee45

    Lee45 Member

    59
    5
    May 28, 2017
    Doesn't a manual valve body cause the line pressure to be extremely high and cause a lot of wear?
     
  8. RS1979

    RS1979 Veteran Member Lifetime Gold Member

    2,910
    367
    Jun 18, 2013
    Memphis, TN
    I’m sorry. I meant a tranny I had years ago. The one in my Camaro doesn’t have a manual valve body.
     
  9. camaro71/holland

    camaro71/holland Veteran Member

    968
    29
    Aug 27, 2003
    The Netherlands
    Constant high line pressure can be harsh for daily/street driven trans, but has nothing to do with a manual VB.

    When you install a transbrake you lose the vacuum modulator and get constant high pressure. These cars have MVB since there is no vacuum signal controlling the downshifts.
     
  10. Lee45

    Lee45 Member

    59
    5
    May 28, 2017
    Well I broke the first rule of fixing anything. Do the easiest thing first. When I swapped in the transmission my brother set up the shifter cable. He lined it up with park but didn't check any other gear and when I checked it yesterday it wasn't even close to being in 1st when pulled to low. Seems to be a common problem with B&M shifters. Lined it up in neutral to split the difference. Goes far enough to engage the parking sprawl and finally I can hold first and pull it whenever I please. Going to get a nicer shifter when I got the money. Also played with the vacuum modulator and have it shifting into second at a pretty decent time. all in all, the trans is working much better.
     

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