TH400 shift points

Discussion in 'The "Juice Box"' started by matt68gs400, May 18, 2019.

  1. matt68gs400

    matt68gs400 Well-Known Member

    14CCD9C1-C711-4D56-9D54-85C197783A14.jpeg ok... so my car shifts terribly at wide open throttle. It used to shift at 4800 rpm from 1st to second gear. Then just a few seconds later it shifted from 2 to 3 at about 4400.

    I took out the governor and shaved off the inner weights. Went from 11.6 grams to 10.6 grams each. Now it shifts at 5200 and 4500. I have one picture of a shaved weight.

    How do I extend 2nd to 3rd, so it will shift at 5,000 and not 4.400? Change Springs? Outer weights?

    Thanks!
     
    Last edited: May 19, 2019
    scubasteve455 likes this.
  2. Nailhead Ronnie

    Nailhead Ronnie Life's 2 Short. Live like it.

  3. Mark Demko

    Mark Demko Well-Known Member

    I went thru this on my 350/350 GS.
    First thing I would do is buy the weight and spring kit from B&M
    Its a change and test process that's pretty time consuming, so you have to be patient:cool:
    On my T-350, I set it up to autoshift 1-2 @ 6000 rpm
    It will autoshift 2-3 @ 5500, I haven't figured that one out:rolleyes:
    So what I do when I want a 6000 rpm shift from 2-3 at the track is start off with my shifter in second, it will autoshift from 1-2 @ 6000 and no further until I manually shift to third @ 6000 rpm.
     
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  4. matt68gs400

    matt68gs400 Well-Known Member

    Everything is controlled by the output shaft speed. The outer primary weights are all out at around 720 rpm, according to my 71 manual. Then inner weights and springs take charge.

    I think what I should have done was left one weight alone, the one with the heavier spring. Then shave down the one with the lighter spring. The heavier one would have flung out first (first to second), then the lighter one at a higher speed (second to third). Oh well, live and learn. Problem is that i don’t have a welder to put material back.

    these inner weights and springs act on the modulator valve, and they are somewhat affected by each other, but you don’t want them identical. I’ve heard the story of Buick’s shifting to third by the time they cross the Intersection. My weights were the same and the springs were different, so really, it was probably spring pressure only that was causing the shifting
     
    Mark Demko likes this.
  5. Mark Demko

    Mark Demko Well-Known Member

    I don't know about the T-400 in the A body, but the T-350, I have to move the crossmember back outta the way every time I needed to remove the governor cover:mad:
     
  6. matt68gs400

    matt68gs400 Well-Known Member

    Lol. No issue, easy access. I don’t even put the car on ramps for the th400, as it drains an extra quart of fluid on the ramps. Remove three bolts. Keep the lower left on but loose, and spin the cover counter clockwise. :)
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Springs will move the shifts apart. Weights get you in the ball park, springs fine tune. Yes the B&M kit is expensive, that's the hobby.
     
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  8. matt68gs400

    matt68gs400 Well-Known Member

    Yes and..... it’s still fun to do things the old fashioned way too.
     
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    :DYes, but I am unaware of anyone selling just springs, so unless you want to experiment by looking for springs in a hardware store, or clipping coils, buy the kit.:)
     
  10. Bigpig455

    Bigpig455 Fastest of the slow....

    I did find a source for the springs, but you have to know what youre replacing first...Matt, PM me.
     
  11. matt68gs400

    matt68gs400 Well-Known Member

    So I did get a Governor with some weight shaved off the nose at an angle and lighter than stock springs. Then the car wouldn’t shift up to redline. It also shifted at higher rpm when cruising. So I kept putting in heavier springs. Now it shifts at 4800 from first to second and “redlines” from second to third. When I say redline, i mean that i let off the gas around 5,400-5,500 rpm.

    So back to the drawing board. If I put in another heavier spring, it will shift even lower. I’m going to put in one heavy weight and start over with lighter springs.
     
  12. matt68gs400

    matt68gs400 Well-Known Member

    12th time is a charm! Put in a second Governor from the tranny shop. Stock weights. Looked like it had lighter springs. So I thought, what the heck. Works great! 5,100, 5,100. Got lucky.
     
  13. matt68gs400

    matt68gs400 Well-Known Member

    So with a 120 pound passenger in the car, it was shifting at 4700 now. I’ll have to check it again and see if it still shifts at 5100 with just me in it.
     

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