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TH 400 shift points

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BigJohnson, Aug 27, 2001.

  1. BigJohnson

    BigJohnson 1/2 ton status

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    Is there a way to change the shift points on a TH-400? Mine doesn't stay in gear long enough. Can you tinker with the governor to change the shift points? Or maybe change governors to one out of another tranny with different shift points? Any thoughts would be helpful.
     
  2. DesertDueler

    DesertDueler 1/2 ton status

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    They make an adjustable vacuum control that goes on the side of the TH400 where the vacuum line goes in. It uses an alen screw to adjust it. You put it on drive it and see if it needs to go higher. Just keep playing with it till you get it right. I believe Summit has them, or probably any speed shop. They are a popular item.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  3. DesertDueler

    DesertDueler 1/2 ton status

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    By the way it uses vacuum to shift, not a govener. This piece adjust the vacuum. Very easy to install, just take the old piece off and put the new one on. There is just one bolt holding it in. Just follow the vacuum line down to where it attaches to the tranny and thats it.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  4. BigJohnson

    BigJohnson 1/2 ton status

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    Cool. I'll give it a try and see what happens. Thanks for the info.
     
  5. DesertDueler

    DesertDueler 1/2 ton status

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    No problem.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  6. 90K5

    90K5 1/2 ton status

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    You could also get a shift kit for it. Makes ot shift higher and firmer.

    90K5
     
  7. Wheels

    Wheels 1/2 ton status

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    Not to be the bearer of bad news, but low pump pressure will also cause the tranny to have low shift points. Transgo makes a kit to modify your shift points.
     
  8. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    thats why i like the TH350. a grinder and an hour you can shift a lot hight RPM....
    but yes DD is right, follow the vacume line and adjust the screw.
    Grant

    1974 Chevy Blazer Cheyanne. but it is on 33's now, with saggy old springs. i am in Yuma Arizona if ya got any parts for me.
     
  9. Smitty

    Smitty 1/2 ton status

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    I picked one up from CarQuest. Made by Poineer Inc. Part number 747024.

    Smitty
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    More bad news : ) Thats not correct. TH400 has a governor just like the TH350, 700-R4, and 200-4R. 4 bolt cover on the drivers side, same location as the Th350 except that cover is pressed in/held in with a wire.

    Adjustable modulator only allowed me to change shift points on my TH400 by a MAXIMUM of 5MPH. Definitely not enough. Change the governor, or adjust it. Do a search on yahoo for governor calibration kits or something like that. Someone makes one. They operate similar to mechanical advance, and you CAN grind/add weight to them, as well as mess with the springs. They are VERY sensitive to change in weight though, from what I have heard.



    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
    No anti-theft measures on your truck? No pity when its stolen
     
  11. BigJohnson

    BigJohnson 1/2 ton status

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    Thanks for the input. I found a recalibration kit at Summit Racing. I think I'll give it a try.
     
  12. Smitty

    Smitty 1/2 ton status

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    Just how far are you trying to change the shift points???

    Smitty
     
  13. BigJohnson

    BigJohnson 1/2 ton status

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    Smitty, I don't really know. My engine doesn't ever seem to build up enough rpm when the transmission is shifting. When I shift the tranny manually and let it build up some rpm it runs alot better. I don't have a tach so I'm not sure exactly what rpm the shifts are happening. I figured I would buy the recalibration kit and just tinker with it.
    I hope this will cure my lagging engine problems. Any thoughts would be appreciated.
     
  14. DesertDueler

    DesertDueler 1/2 ton status

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    The turbo 400 I have in my firebird has a stock vacuum piece, and a stock governer, and it shifts between 4000 and 4500 when Im in the throtle. The only thing I did was put that 25 dollar B&amp;M shift kit in it. So far the tranny has held up to 3 yrs of drag racing and street abuse. I am building another for race season for just in case. Three years for a tranny in drag racing is very good.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     

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