72 Skylark, kickdown cable operation

Discussion in 'The "Juice Box"' started by mattd3933, Jun 26, 2020.

  1. mattd3933

    mattd3933 Member

    My 72 Skylark has the original th350. since ive had it, i have never had the kickdown detent cable installed, it just seems to be a little to short to get it to the gas pedal . The trans does fine in first and second, but it is slow and kinda random shifting to 3rd. It also has delays going into reverse.

    I was doing some trans research on switching to a 455/th 400 and ran across this info.

    "The pre-'81 TH350 uses a detent cable to activate the gearshifts and passing-gear kickdown. You must use a detent with these units, or the transmission will not have a passing gear, plus the shifts will be very sluggish."

    I already know i dont have a passing gear, but can someone explain How the detent cable being off could affect the other shifts being sluggish. Could that be part of my buggy 3rd gear?
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    The THM350 and 400 both have a detent system, the 350 uses a cable, the 400 uses an electrical system. Both transmissions use 3 inputs to determine shift points, engine vacuum (modulator), road speed (governor), and throttle position (detent). Each input generates fluid pressure, it's like a tug of war between the 3 to determine shift point and feel. If one input is wrong, or missing, you'll have shift point problems. You'll probably hear from some guys that they haven't had it connected for years and the transmission is fine. On the 400, if the kick down system isn't working, the transmission will short shift at WOT. The THM350 cable connects to a detent lever and valve inside the pan. IMO, it has an effect on shift points.

    Not sure what you mean by the cable being too short. If you pull on the cable, it should pull out smoothly with some resistance. If you let it go, it should go back into the transmission like it is spring loaded. If it doesn't, either the cable is binding, or something is amiss inside the pan. The detent cable should reach full travel at the same time as the throttle is wide open. If the cable won't pull out that far, something is wrong. Find out what is wrong, and fix it. Then see if your problems go away.
     
  3. BrunoD

    BrunoD Looking for Fast Eddie

    Maybe the cable he has is from a 300.but it should be the right one if it came with the car,Bruno.
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Wouldn’t the 300 be coupled to an ST300? That would be electric kick down like the 400.
     
  5. mattd3933

    mattd3933 Member

    Larry that is some great info. thanks. Ive been into the pan recently, we put a shift kit (transgo) in and i tried my best to make sure everything was moving freely in the valve body. before the shift kit i didnt have 3rd at all, still had reverse issue. Wwe went in tried to make sure everything was clean and moving, installed springs/balls, replaced my modulator, replaced filter, front main seal and rear output shaft seal then put it back together. added a can of the lucasoil transfix with the new trans fluid. Figured maybe we freed something up in the valve body or maybe something else we did found 3rd gear.

    I will try to get some pictures later of where the end of my detent cable ends up, and the distance it needs to cover but doesnt, everything looked good inside for the cable when we changed the clip on it that came with the shift kit. thanks again for all the info folks
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Matt,
    If you pull on the cable, do you feel a smooth resistance? And if you let it go, will it pull back into the transmission? If it does, it should be OK. Maybe you have the wrong cable? The Chevy cables connected to the carburetor, not the gas pedal, so there are different cables.

    It should look like this,
    DetentCableGasPedal.JPG
     
    Last edited: Jun 27, 2020
  7. mattd3933

    mattd3933 Member

    This is as close as i can get to the hole to mount the cable to the firewall. and some pics of how it looks by the pedal, it does look slightly different than yours. ive routed it a few ways and this is as close as i can get it. sorry for the delay, i got distracted then had a death in the family.

    [​IMG][​IMG][​IMG]
     
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Last edited: Jul 3, 2020
  9. telriv

    telriv Well-Known Member

    Those correct cables were available at NAPA. Don't know if they are still available or not. Worth a call.

    Tom T.
     
  10. mattd3933

    mattd3933 Member

    good info folks, if i remember right i can probably change out the cable without pulling the whole trans, just the pan. but i would have to look back at some of my pics from the shif kit install to be sure. really though i feel like my trans needs a rebuild, the 3rd gear delay COULD be something to do with the kickdown cable, but the delay i get going into reverse probably is another issue. one person said that 3rd and reverse work of the same friction plate in there and that is probably worn at least.
     
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    No need to even drop the pan. You will lose some fluid though. Unbolt the cable at the trans, pull it out with the link, and swap them.

    It does sound like you have other transmission problems.
     
    Last edited: Jul 3, 2020

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