1. Syleng1

    Syleng1 Karma is real and Life is short... FABO Gold Member

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    so I’m 99% sure I can use a 66 a-904 valve body in a 74 a-904 trans right? As long as I use the single stud neutral switch with the 66 valve body.

    Car is a 66 Abody with small block.

    Transmission expertise Opinion welcome.
     
  2. fishy68

    fishy68 Tyr Fryr's Inc. FABO Gold Member

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    Shouldn't be a problem. Only thing you'll lose is part throttle kickdown
     
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    • Syleng1

      Syleng1 Karma is real and Life is short... FABO Gold Member

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      “Part throttle kick down” ?!?
      I’ll research what that means even though it sounds pretty self explanatory.
      I have a 66 formula s I was thinking about robbing the trans for on my build in the shop. I rebuilt a 74’904 2 years ago and put it in a rebuild of my other 66 after a very complete and I do mean complete car overhaul.

      In the valve body I put a shift kit and a deep oil pan. It’s acting flakey for its initial trials so I was going to swap out the valve bodies to see if it was valvebody or trans related. It could even be suction side of filter. Deeper pan has a filter extension that could be leaking provide fluid only under high revs. I have no movement at lite throttle, it will shift thru gears but only on the lift. On the ground I need to get to 2000rmp before the car will slide fwd like it has a trans brake... and it does not.

      It’s going to be something simple. I need to double check the kick down cable (I went lokar cable over linkage to save space for larger exhaust). Maybe the adjustment slipped. When I pull the valve body I can re air check trans for leakage.
       
    • CudaFactHackJob

      CudaFactHackJob FABO Gold Member FABO Gold Member

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      Sounds like maybe you installed the converter valve upsidedown. Asfaras the pump sucking air with an extended filter..nope, cuz the fluid level should be above that juncture anyway.
       
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      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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        Check the cases very carefully, to make sure the passages around the accumulator are the same. about the mid 70s the cases were changed and IDK if the 66 and older will transfer to a 74.
        As to the neutral switches, I don't think they are interchangeable. But IDK for sure either. But pretty sure the hole-sizes are different.
         
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        • Syleng1

          Syleng1 Karma is real and Life is short... FABO Gold Member

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          If there is a major problem I’m just going to drop out the 74 and rebuild the whole 66 a-904. I don’t like messing around but if I did something during the rebuild - like missed something during the valve body shift kit install then I’ll just start over. Transmission stuff is easy but modified valve body stink. No trouble shooting them like a factory one.
           
        • fishy68

          fishy68 Tyr Fryr's Inc. FABO Gold Member

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          Part throttle kickdown was added to later models (71 and newer if i remember correctly) so you didn't have to mash the pedal all the way to the floor for it to kickdown from 3rd to 2nd at moderate speeds.
           
        • Syleng1

          Syleng1 Karma is real and Life is short... FABO Gold Member

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          So I drained the pan and the fluid was brown- with less than 2 hours on engine just breaking in the cam and tweaking the fuel injection and no road time on the trans brown fluid is something is overheating.

          I pulled the pan and some black residue but no chunks or parts. I pulled the valvebody and the detent ball for the shift pawl fell out and the part rod assembly stayed behind. Looks like the e clip broke?!? Found it in two in the magnet in the pan.

          I air checked the trans and all is working as it should. With 125psi from compressor I had good piston travel (thud) But a little leakage from the forward clutch pack. Rev/ low (tail shaft side ) no leakage. I’m not sure how much is okay. I’m not expecting 100% seal. Now to look at valvebody and see if the spool valves are where they said they should be. It’s odd, I rebuilt over 100 trans in my life professionally perfectly- my car and one hickup and I’m ready to pack it in. Boy the brain works soooo strangely.
           
        • oldkimmer

          oldkimmer FABO Gold Member FABO Gold Member

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          Ur only supposed to use 30 lbs to do an air check. Kim
           
        • CudaFactHackJob

          CudaFactHackJob FABO Gold Member FABO Gold Member

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          Black residue is fiber dust.
           
        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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          Don't forget to install and adjust the KD mechanism which is actually the Throttle-pressure controller.
           
        • Syleng1

          Syleng1 Karma is real and Life is short... FABO Gold Member

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          Nothing in the FSM says 30psi. Line pressure is upwards of 300 psi of trans fluid.

          I found An issue with low line pressure. Popping a known good valve body this week. Double checked my adjustments - all good.
           
        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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          IIRC, the line pressure spring is very similar in size to another weaker spring in the VB. It wouldn't be the first time someone accidentally swapped them. I think the wrong spring mightacome from the rooster-comb detent.But I really don't recall.
           
        • CudaFactHackJob

          CudaFactHackJob FABO Gold Member FABO Gold Member

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          I doubt the clutch pack was leaking; probably just blowing past the rings.
           
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          • Syleng1

            Syleng1 Karma is real and Life is short... FABO Gold Member

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            Well- known good valve body and issue is corrected. Took car on its first drive on 3 years. Shifts awesome so the original valve body I’ll tKe apart and diagnose against factor service manual to figure it out.
             
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