TH400 - No 2-3 shift at WOT

Discussion in 'The "Juice Box"' started by Bigpig455, Sep 8, 2018.

  1. Bigpig455

    Bigpig455 Fastest of the slow....

    Took my 71 GS to the track last night and had no WOT 2-3 shift. The car has a untouched 69 PS code TH400 from a Pontiac 350 HO car that has been bulletproof with quick, drama-less shifts. It does not have a shift kit, and had likely never been opened.

    I did a search here, and a few other forums to see who's had luck correcting the issue and how, just need some feedback:

    Modulator and line - shifts fine at part throttle
    Kickdown switch - functions fine, has power. Do not hear solenoid click in pan, but I dont hear it on a known good car either.
    Governor - has known tune for 5300, and 1-2 shift is spot on

    So that leaves me with three possible things left? The detent solenoid sticking, 2-3 shift valve sticking, or an internal leak applying pressure to the clutches?

    The car exhibits no other issues, and will 2-3 shift as soon as I get out of WOT.

    This really pissed me off cause it was GREAT air last night, and my 1/8th miles would have put me deep into the 12's. Has anyone else had the same circumstances, and if so, how did you correct it?

  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Governor. Pull it out and inspect it. Look at the weights and springs and make sure the valve moves, and isn't gummed up. You should be able to hear the detent solenoid click by applying 12 volts directly from the battery. You need a quiet environment.
  3. telriv

    telriv Well-Known Member

    2-3 shift valve sticking. Remove & clean. Replace valve body gaskets. Drill holes in shift plate while it's out. Governor valve sticking.
  4. Bigpig455

    Bigpig455 Fastest of the slow....

    thanks Tommy and Larry - i figured I was in for pulling the valve body out. It's a good excuse to reseal anyway.
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Start with the easy stuff first. Could it be a sticky shift valve? Sure. Is that the more likely cause?
  6. Bigpig455

    Bigpig455 Fastest of the slow....

    I took an extra solenoid i had out to see how loud it might be cause I didnt hear it on my 73 either.... I cant see it being the governor if the 1-2 shift is perfect and right on the RPM point.
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    It's a lot easier to check the governor than to drop the pan. It could still be a dislodged or broken spring.
  8. Bigpig455

    Bigpig455 Fastest of the slow....

    fair enough - I'll keep you posted
  9. Steve Schiebel

    Steve Schiebel Well-Known Member

    This is a timely post for me, I'll be watching responses closely and pulling my governor to inspect. Yesterday I was at WOT on a long, rising, deserted highway entrance ramp when the same 2-3 missed shift occurred. 1-2 shift was normal at the 5300rpm I had set the governor at. I was at 100+mph and 5500rpm when I backed off due to no shift and entering the highway. Spooked me, but car ran out just fine, shifted normally when not at WOT the next 40 miles to home.
  10. Bigpig455

    Bigpig455 Fastest of the slow....

    so I think I found the issue, but havent been able to road test yet.

    I modified this governor, and I ground the inner weights to a specific gram weight on a grinding wheel leaving a very sharp edge on the lower outer "flyweight" part of the weight. Over time, as that sharp edge slapped back under spring pressure against the outer weight, it almost cut a "shelf" into the outer weight at that contact point, and the edge of that "shelf" was catching and holding the inner weight in place, not allowing it to swing inward and let the detent valve move in the governor body as line pressure rose.Lesson learned: fine finish any modifications prior to assembly.

    I did the valve body too, and polished the 2-3 valve with emery cloth, also replaced the detent solenoid to be on the safe side, but there was no gunk or varnish anywhere. I'm waiting for my driveshaft to come back from the balancer to put it all back together and road test. If all goes well I'll be up and the Supercar Nationals at LVD this weekend. Looks like good air too!
    Julian, johnriv67 and techg8 like this.
  11. johnriv67

    johnriv67 Well-Known Member

    See you there! Look for the only green 1967 Riviera in New England, as far as I have seen. I'll say it until proven wrong
  12. telriv

    telriv Well-Known Member

    It will be great to see you again Rhett. Will be there with another friend either racing or at the swap meet.

    Tom T.
  13. Bigpig455

    Bigpig455 Fastest of the slow....

    I would have been great to see you too Tom, but now it looks like I'm taking the kids to the beach instead...I am headed up for the track rental today, and if I'm right the Supercar guys are running again next weekend too, so maybe I'll make that one. I did put the car together last night, but Ill be road testing it on the way to the track.. wish me luck.
  14. scubasteve455

    scubasteve455 Well-Known Member

    Rhett That 71 looks bad ass

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