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Transmission trouble? Turbo 350

Discussion in 'The Hokey Ass Message Board' started by 55 1ST SERIES, Feb 14, 2013.

  1. Ok, here's the story...
    I did a trans swap from a cast iron PG to a new Jegs th350 in a 58 Chevy. It had a good running 283 with a 600 Holley carb w/ adapter on the stock cast iron intake. After the swap, the car never really ran right. The engine ran fine, but from a stop it felt like you had your foot on the brake while giving it gas. It had a 1800-2200 rpm stall converter.
    While trying to figure this thing out over several weekends, the engine developed a slight tick. Not a rod knock, but too loud to be a lifter. Sounded like maybe a wrist pin. So we had the 283 rebuilt. Basically a stock rebuild with a summit 1101 cam.
    Before dropping the engine back in, I swapped out the converter for a stock replacement, thinking the reason for the bog from a stop was the higher stall converter. I also replaced the intake with a C3B Edelbrock but kept the same carb. After dialing the motor in & breaking in the cam, we still have the sluggish issue. I don't think it's a timing issue. It's set at 4* advanced. It's not missing and I can't find any vacuum leaks. I think it could be the transmission but I'm not sure. There is also a noticeable vibration before each up shift. I know it should have way better acceleration from a stop since the Th350 has a much lower first gear than the powerglide. It doesn't. It's way worse. Any ideas? I'm getting ready to pull the tranny & try another one.

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  2. OldFord39
    Joined: Aug 23, 2011
    Posts: 64

    from Monroe, Wi

    A couple of questions are you using the same shifter as the powerglide? If you are able to put it in manual low do you still have the sluggish issue? In drive you will run about 60 Psi of line pressure, when in manual low it would be slightly over 90 psi. from what you describe it would seem to indicate that the transmission is starting out in second. In drive 1st gear is controlled by the forward clutch being applied and the low roller clutch being applied in manual 1st the low roller clutch is taken out of the equation as the forward clutch is applied and the low/reverse clutch is applied. The problem you described could be caused by the second gear clutch being to tight / the kickdown band draging the governor sticking the kick down valve stuck or out of adjustment, manual valve not indexed properly to the gear selected. To
    diagnos an automatic alot of information can be obtained from a pressure gauge and knowing what clucthes are applied in what gear as a three speed automatic needs two clutched applied for each gear if a third is dragging you will experiance a very sluggish condition if three are fully applied it will be like the brakes are on. let me know what the transmission feels like when you manually shift it. If you buy a gauge you will need one that goes to 300 PSI as reverse will run about 240 Psi and a hydraulic hose 6 to 8 feet long with 1/4" pipe thread S & G tool aid is probably about the cheapest place to obtain a gauge.


  3. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    from Phoenix AZ

    Kick the initial timing up to 10-12* ,4 ain't enough. And make sure both manual and vacuum advances are working.
  4. Old ford,
    I'm using shift linkage from the Truck & Car Shop in Orange,CA. It's supposed to be for a PG to TH350 swap.
    It feels the same starting out in D or 1st. I can feel the upshift from 1st to 2nd & 2nd to 3rd, so I don't think it's starting out in 2nd. I'm going to see if I can borrow a pressure gauge. Thanks for the ideas.

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  5. hoop98
    Joined: Jan 23, 2013
    Posts: 1,363

    from Texas

    Stall test the converter, in a safe location, lock the brakes and apply full throttle.

    The engine should run up to about 1500 RPM, if it is down to about 1100-1200 you likely have a converter issue. The most common failure is the one way clutch for the stator.

    The converter is not involved from 10MPH to the 1-2 upshift so if it feels sluggish there it is probably not the transmission.

    You may want to verify your TDC mark is accurate;

    Use a spark plug-type piston stop tool. Set the plug hole-mounted piston stop to contact the piston close to TDC.
    Rotate engine until the stop just contacts the piston- mark the location.
    Rotate in the opposite direction until the piston is stopped
    Half way between the two marks TDC.

    Turn the engine carefully.

    Video Instructions.

    If you don't know the distributor advance you can use a dial back timing light to check mechanical advance.

    The engine is going to want 32-38 degrees advance by 3000 RPM. I would set it at 36 to start and tune from there.

  6. Hoop,
    I'll try the stall test. I'm pretty sure my TDC mark is accurate. What makes me think it's a tranny issue is that it felt the same before the engine rebuild. And the engine ran great, but developed the wrist pin noise, so we pulled it for the rebuild. Also, it felt the same with either convertor. I'll have to verify if the vacuum advance is working ok, as it is the original distributor. Thanks.

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