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Thread: Any Chevy TH400 Experts?

  1. #1
    Senior Member RACING JUNKIE
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    Any Chevy TH400 Experts?

    Finished the 454 for the Green Monster and the motor runs great. Put rear brakes in the C/20 as well. However the trans is now a problem.

    The TH400 goes from 1 - 2 fine, but doesnt want to go into 3 until near 4500 rpms.

    I replaced the vac modulator and have over 15 vac at modulator off intake.

    I cleaned and inspected the governor. Looks fine and valve moves.

    I put a static vacuum pump to keep it at 20 and drove it with no shift from 2 - 3

    I am thinking kickdown- disconnect the kickdown switch/solenoid at trans? Its pedal actuated.

    Any ideas?

    Scorp
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  2. #2
    Moderator RACING JUNKIE Harbone's Avatar
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    disconnect that electric kickdown first and drive it, it might be stuck. Is the switch at the top of the gas pedal?
    Chris

    As close to "Normal" as I can get...

  3. #3
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    i know there is a shift adjustment screw in the vac modulator ...... just need to stick a lil reg. screwdriver in where the vacuum line goes on and you can adjust the shift point...... just another idea :wink:
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  4. #4
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    Quote Originally Posted by harbone66
    disconnect that electric kickdown first and drive it, it might be stuck. Is the switch at the top of the gas pedal?
    Chris

    The switch is at the front of the pedal, two leads with clip to switch, under car orange wire to solenoid on driver side of trans. The solenoid is covered in crap and the orange wire is wasted with part of the shielding missing.

    It starts good and goes from 1 - 2 pretty easily and then just stays in 2 and the RPMs climb.

    Scorp
    Cowards often find courage behind a keyboard. If you want to get personal, look me in the eye when you say it, and be man enough to deal with the consequences.

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  5. #5
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    Quote Originally Posted by fast75vega
    i know there is a shift adjustment screw in the vac modulator ...... just need to stick a lil reg. screwdriver in where the vacuum line goes on and you can adjust the shift point...... just another idea :wink:
    Read that. Counterclockwise = lower shift points right? Havent tried that yet.

    I also think Trans may have a shift kit- when I pulled the small piston behind the modulator it was missing the spring. I understand that a shift kit will eliminate that spring.

    Dont know much about Th400s, stick to 4 speeds usually.

    Scorp
    Cowards often find courage behind a keyboard. If you want to get personal, look me in the eye when you say it, and be man enough to deal with the consequences.

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  6. #6
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    I never hooked my kickdown wire back up when I pulled my TH400 out of my -get this ...'72 C20 :wink: -and stuck it in my Olds. It upshifted and downshifted just fine. Maybe the problem is elsewhere?Sounds like the valve that the governor is supposed to slide may be sticking. it definitely sounds like a governor issue,but you said that checked out.Can you see if that valve is free?

    My TH400 has a manual valve body in it now. You are welcome to the stock one that came out of it if you end up thinking you need one.It has a low level B&M shift kit in but is in perfect working order. Just let me know if you want it. All I ask for is shipping costs,please.
    "The problem with quotes on the Internet is that you cannot confirm their validity"- Abraham Lincoln

  7. #7
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    Quote Originally Posted by olds48
    I never hooked my kickdown wire back up when I pulled my TH400 out of my -get this ...'72 C20 :wink: -and stuck it in my Olds. It upshifted and downshifted just fine..
    i never hooked the elec kick down back up either and it shifts up and down just fine too

    scorp, i dont remember which way was what anymore? just mark the handle of a screwdriver and count each turn... then drive it... ad try the other way and drive it.... lol after going though 3 700r4's in my suburban pulling my drag car around after just 2 years..... i got one of my 400 turbo's i had sitting in my garage and put her in there been 3 years now and going strong.... just had to adjust my shift points cause it wasnt right :wink:
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  8. #8
    Moderator RACING JUNKIE Harbone's Avatar
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    unplug that kickdown wire first and see what it does...
    Chris

    As close to "Normal" as I can get...

  9. #9
    Senior Member RACING JUNKIE
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    I thought only the aftermarket modulators were adjustable?
    "The problem with quotes on the Internet is that you cannot confirm their validity"- Abraham Lincoln

  10. #10
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    Quote Originally Posted by olds48
    I thought only the aftermarket modulators were adjustable?
    not sure.... but i got 4 or 5 400's and everyone has the adjuster in the vac mod. the kick down cable uses 12 volts to work and if you got no switch or power even going to it... it wont even do anything if it was plugged in :wink:

    i had a camaro i builtand put a 400 tranny in it...i just hooked the power to a toggle switch and then ran it from there to the tranny plug.... i was playing around one day and found if you are sitting still and turn it on... you can rev the car up to like 3500ish like a stall converter before it takes off..... oh the fun i had with that car. .... lmao
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