th350c ?

Discussion in 'The "Juice Box"' started by gt750jim, May 19, 2016.

  1. gt750jim

    gt750jim Well-Known Member

    a while ago i posted that my car (71 skylark) was having trouble with a stuck torque convertor i ended up swapping it out now a friend of mine took a look at it and said "oh look a th350c don't see many of them" then he explained the extra shaft sticking through the center of the drive with o rings on it was for the lock up torque convertor ! were these ever a option on the 71 skylark ?
     
  2. Brad Conley

    Brad Conley RIP Staff Member

    Nope. 350C's first appeared in the early 80's to aid in fuel economy.
     
  3. gt750jim

    gt750jim Well-Known Member

    oh well looks like someone stuck one in my car before i got it ! any idea how the lock up was controled as the was no extra switch's in the car ? and the wiring to the trans looked stock
     
  4. rmstg2

    rmstg2 Gold Level Contributor

    The wiring to the trans? If it has wiring it might be for the lockup, other wise there wouldn't be any wiring. Unlike T-400s the 350 has a kickdown cable.



    Bob H.
     
  5. gt750jim

    gt750jim Well-Known Member

    the is a square 4 pin connector drivers side of the trans but only one wire looking at the trans top left in the connector the wire is green and go's into the loom it all looks stock ?
     
  6. Bad Boattail

    Bad Boattail Guest

    Do you also have a 4-pin brake switch installed?

    Someone did a lot of work to get the lockup working if it's not activated by a manual witch.
     
  7. gt750jim

    gt750jim Well-Known Member

    no the was no 4 pin brake switch but the was a vac switch attached to the manifold ?
     
  8. HotRodRivi

    HotRodRivi Tomahawks sighted overseas

    There you go , when u step on the gas vacume drop drops u out of lockup . I had one on my 700 but it was to slow for me . Plus I only want lock up on the freeway. , so I put a switch , works instantly
     
  9. gt750jim

    gt750jim Well-Known Member

    problem was it was stuck locked up ! it would stall the motor if you wore in traffic
     
  10. BigTodd

    BigTodd Well-Known Member

    Hello gt750jim, did changing the torque converter fix your issue with the engine stalling at low RPM's? I too have the same problem, engine will lag down and stall coming to or sitting at a stop sign. It also will die when put into reverse. This seems to happen more once the engine and tranny have warmed up. While the engine is lagging if I shift into neutral the engine pops right back up and runs perfectly. I've checked all vacuum sources and they are good. I'm changing the vacuum modulator today to see if it helps, if not the torque converter is next. Sounds like you and I have been living the same experience with the exception I do have stock original TH350 not a TH350C.
     
  11. gt750jim

    gt750jim Well-Known Member

    mine did not stall in reverse and i swapped the lot for a 200r4 that i had spare
     
  12. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    In Jim's case, the THM350C has a lock up torque converter, and the converter clutch was stuck on for some reason. Thats like dropping the clutch in a manual transmission at idle speed, instant stall.

    How does your engine run otherwise. You still have your initial timing at 4* BTDC?
     
  13. BigTodd

    BigTodd Well-Known Member

    Hello Larry, I believe I am sitting about 8 to 10 Degrees BTDC at idle after doing my best to power time the engine. I have a stock set up engine and trans. I've had a few threads about the work I have done to the car but the overall problem of the engine stalling coming to a stop still persists. The engine runs great, starts right up, idles smoothly, and rev's up nicely with no hesitation or bogging. Once I put it into drive the car lunge and drops down a couple of hundred RPM's. Most of the time am able to drive for about 10 minutes, start and stop but once I accelerate a few times and everything comes to operating temperature it starts stalling when I come to a stop.

    When I slow to a stop I hear the trans stepping down through the gears, while sitting at the stop the engine will sound like I have a manual trans and the clutch is not pushed down all the way. I can hear the engine struggling to keep running. As soon as I move it into neutral, the engine pops right back up to a normal idle, rev'ing just fine. Back into drive, bogged back down. Once I start moving forward everything is fine.

    This Trans has always had a leaking problem from the speedometer gear seal, I finally replaced the seal so no more leaks. But there were several times that I drove the car when it was low on trans fluid. I wondering if those times I and or the previous owner drove with low fluid has damaged the function of the torque converter. The trans itself shifts fine, strong kick down and passing gear, no slipping. It does have a shift kit and still will bark the tires going into second gear. The only issue is the drag on the engine when sitting still in gear. I feel the torque converter has tightened up to the point it's not allowing enough slippage while at a stop.
     
  14. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Torque converter problems usually have symptoms of a stator malfunction. Either the vehicle has poor acceleration or top speed is abnormally low. I don't think running low on fluid would damage the torque converter, but a previous owner could have replaced it with the wrong one. If you do get a new converter, I'd give Jim Weise a call.
     
  15. RUFF

    RUFF Member

    Does the 350c have a kickdown cable? In the Gs I just bought the po told me replaced the 2 speed with a 350 from a 84 Cutlass because the 2 speed was making the car turn to many rpms when cruising. I had a closer look today and it has the plug on drivers side and a kickdown cable but nothing plugged in the plug.
     
  16. gt750jim

    gt750jim Well-Known Member

    the trans on my car (the th350c) had no kick down cable just a vac line feed
     
  17. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Both the 2 speed and the THM 350 have a high gear of 1:1 so no difference in RPM. The lock up torque converter can reduce RPM about 150-200 RPM.

    AFAIK, all THM 350's use a kick down cable.
     
  18. RUFF

    RUFF Member

    The trans I have has a kickdown cable, a plug on the drivers side and a modulator valve. Does the 350c have all of these?.
     
  19. gt750jim

    gt750jim Well-Known Member

    mine has all these ... the only way i knew it was a 350c was the extra drive that runs inside the convertor
     

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