Questions how to fix 700r4 hard 1-2 shift

Discussion in 'Transmission & Driveline Topics' started by RockinZ, Feb 7, 2010.

  1. RockinZ

    RockinZ Veteran Member Gold Member

    1,468
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    Oct 18, 2008
    Montreal, QC, Canada
    Hi Guys,

    My 700r4 shifts damn hard 1-2.

    Here are the mods I made to my '89 700r4:

    .500 boost valve. too much pressure?

    L type accumulator valve assy with pink firm shifting spring. maybe that's it? This one was chosen because it was recommended for a heavy car, but maybe my gear ratio affects this?

    5600 rpm Corvette governor, Corvette servo & piston assy (does not shift that high).

    2600-2800 stall

    I have a 3.73 gear
    Thanks
     
  2. wiseryder

    wiseryder Veteran Member Lifetime Gold Member

    1,721
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    Sep 11, 2004
    belding,mi USA
    Yup, Hopefully Jake will jump in But ,Mine shifts damn hard too..
    You can rock yer Molars loose sometimes ,lol
    Wife hates it ..
     
  3. green 1977

    green 1977 Veteran Member Lifetime Gold Member

    3,679
    1
    Aug 18, 2003
    On Wisconsin!
    My 700 shifts hard too..... Lol .... But my th350 shifted harder so wifey thinks this is an improvement:D
     
  4. Twisted_Metal

    Twisted_Metal Moderator Lifetime Gold Member

    24,030
    2
    Feb 26, 2004
    Bloomington, MN
    When you say it "shifts hard"......

    Do you mean under light throttle, heavy throttle or all the time?

    I can't help you myself but this info will probably help Jake diagnose the problem(s) when he sees your thread.
     
  5. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

    8,847
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    Dec 8, 2000
    Republic of Texas
    The 1-2 shift on a 700 can get really brutal, really quick when you do all the improvements to make it live.

    Better band, bigger servo, increased pressure all contribute to the harsh 1-2.

    The problem is that most guys drill the 1-2 feed hole too big.
    Some block the 1-2 accumulator.

    I wouldn't mess with the TV boost valve or any of the pressure regulating parts. Let it have the pressure, it keeps it alive for the 3rd and 4th gears.

    You can check the accumulator, but chances are you will need to pull the valve body down and replace the plate or make the hole smaller for the 1-2 feed.

    You could check the servo and be sure the cushion spring isn't omitted, or even put a smaller servo in, however I like to work with the larger servo and use my feed orificing to control the apply feel.
     
  6. RockinZ

    RockinZ Veteran Member Gold Member

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    Oct 18, 2008
    Montreal, QC, Canada
    lighter the throttle harder the bang. Best is when it's got enough throttle to chirp the tires, then it feels great!

    I can get a softer shift by adjusting the TV cable, but then I loose my kickdown.

    Jake, if I go with the mid range 1-2 spring will that make any difference?

    Thanks!
     
  7. ZS10

    ZS10 Moderator Lifetime Gold Member

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    Jan 18, 2003
    BC, Canada
    I used to adjust the TV cable 2-3 clicks for street and track. Just enough to soften the shift a little.
     
  8. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

    8,847
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    Dec 8, 2000
    Republic of Texas
    I would first look at the servo, because you can do this without even dropping the pan. They sometimes have you omit the cushion spring and install shims to tighten up servo clearance and kill the cushion. I do NOT like this method, even though it is what TransGo does.
    I would look at the 1-2 accumulator next, make sure it's not blocked.

    Then you can go from there. If the servo doesn't cushion it enough, go to the accumulator. If it isn't blocked or has a super stiff spring, plan on installing a new seperator plate.

    I do not like to to adjust the TV cable for shift feel. I like to adjust the TV cable for proper shift timing and pressures. Once the pressures are right and it's shifting at the proper time, if the feel is too hard, you need to adjust this through the accumulators and orificing.

    The biggest thing is the orificing. Most shift kits recommend a hole that is too big.

    2-3 shift feel is somewhat controlled by band clearance (servo clearance). Less is better to a point.

    There isn't really an accumulator for the 2-3 feel, it is the servo release.
     
  9. RockinZ

    RockinZ Veteran Member Gold Member

    1,468
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    Oct 18, 2008
    Montreal, QC, Canada
    There were no mods to the valve body in my trans, just the boost valve, accumulator, servo and governor from PATC. Everything else is stock. oh yeah, and a BTO kit.
     
  10. bigdav160

    bigdav160 Veteran Member

    561
    1
    Jan 11, 2006
    The Great State of Texas
    There's something wrong in you're accumulator circuit.

    Just the Corvette servo and 1/2inch boost valve wouldn't cause an overly harsh shift.
     

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