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Any manual transmission gurus? Clark 390v

Discussion in 'Trucks' started by JThomas7, Mar 3, 2016.

  1. JThomas7

    JThomas7 Well-Known Member

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    So bummed out right now. My water truck has been down for months as I searched for a known good 390v clark tranny. I couldn't find one and finally tore into this one to find first gear seized to the shaft.

    I ended up replacing all the bearings, output shaft and first gear. I bench shifted the thing 1000 times and was pretty proud of myself for seemingly fixing this problem.

    We reinstalled the tranny today and all is good in the forward gears. However it doesn't seem to want to go into reverse. I would say once in 50 shifts it falls into reverse but some times jumps out. It seems like the shift collar just isn't wanting to slide onto the first gear, like maybe the teeth aren't lined up. one thing is there are no syncros on the 1st / reverse shift side. I really don't know where to start here.
     
  2. lantraxco

    lantraxco Senior Member

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    Any chance you have a bent shift fork, due to the original problem? Also, double check the shift cover, there's usually a blocker setup, all the rails have to be in neutral before any one can move out of neutral, may have something hanging up there.
     
  3. JThomas7

    JThomas7 Well-Known Member

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    You're thinking the exact same thing I was. The shifter goes into the reverse position, but it's like it's just not quite far enough to slide the ring coupler over the reverse gear. Of course then again about 1 in 50 shifts it will just fall into place. I just never checked the shift fork stuff because it wasn't a problem before, it shifted into every position, just locked up because it would be in more than 1 gear at a time with first welded to the shaft.

    I will pull the shift cover off though in the morning as it's just something easy to check. I'm afraid I will have to drop the tranny completely to get inside of it.
     
  4. JThomas7

    JThomas7 Well-Known Member

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    trannydiagram.jpg

    Something I also noticed just now while looking the manual over again. On the reverse side of 2nd gear the splits washers and retaining ring show a "Locator ball"
    Possible I lost this taking it apart? I know I didn't put anything like that in while putting it together. Not sure how it could be my issue, of course not sure what it's suppose to do.
     
  5. lantraxco

    lantraxco Senior Member

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    Not sure about that ball. I wonder if it has to do with positioning that #8 hub that splines onto the shaft?

    This is a reach, but any chance that number 6 sliding clutch is not symmetrical? Maybe it's possible to get it in backwards. Or a thrust washer or snap ring isn't exactly where it's supposed to be. Bummer.
     
  6. JThomas7

    JThomas7 Well-Known Member

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    hypothesis.jpg

    Will definitely check all those things

    I have another hypothesis now as well.

    From what I think I know when the transmission is in neutral all gears on the output shaft should be spinning freely. But there's nothing that turns the reverse gear? Does the little ball between 2nd and reverse make reverse freewheel on the shaft etc?

    When I can get it into reverse, reverse works fine. What I'm thinking now is that when the shift collar teeth aren't perfectly aligned with the reverse teeth all the clutching in the world isn't going to make them line up because when I left the clutch out the gears not turning on the shaft?
     
  7. Pops52

    Pops52 Member

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    This is a stretch but something similar happened to me many years ago with a 5 speed spicer in an old bucket rig. Top cover had been loose & gasket was shot so I just used silicone type gasket sealer. Wouldnt go into reverse without 2 men pulling on lever. Turned out just the thickness of the gasket kept the pressure off the reverse fork.
     
  8. lantraxco

    lantraxco Senior Member

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    There should be a reverse idler shaft not shown in that picture that transfers power from the countershaft to the reverse gear, it's turning any time the input is turning.
     
  9. JThomas7

    JThomas7 Well-Known Member

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    hmmmmmmmmmmm. I did seal the top plate with silicone.............. However I can get it to go in the reverse position, just slightly grinds and isn't engaged when the clutch is released.
     
    Last edited: Mar 3, 2016
  10. JThomas7

    JThomas7 Well-Known Member

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    I haven't torn into it yet this morning but I did get in it and drive it around. If I pull onto an incline and shift it into reverse while it's rolling back slowly I can get it to go in pretty much every time.
     
  11. JThomas7

    JThomas7 Well-Known Member

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    Got the top off. One of the "pads" at the end of the shift fork (on the reverse side) is worn way down. Like maybe it would push the ring cockeyed as the other side is still beefed up. Nothing appears bent. I put the shifter into reverse before I popped the top off and the ring was pushed up to the end of reverse but not onto the teeth.
     
  12. lantraxco

    lantraxco Senior Member

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    Sound to me like the fork is maybe worn crooked from when the first gear bearing went South?
     
  13. JThomas7

    JThomas7 Well-Known Member

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    forkground.jpg

    That's what it looks like to me.

    The problem now? Part is unavailable.
    has the part # 236953-R on it. That part # brings up nothing.

    Transmission shop says I need 239140 but it's discontinued.
     
  14. lantraxco

    lantraxco Senior Member

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  15. Birken Vogt

    Birken Vogt Charter Member

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    I was going to say weld it up and be done with it. I might have done that even before looking for a new part. I should think a good machinist would be able to cut both sides in the same plane and 90 degrees to the rail so they push on the gear evenly if you want to be real precise about it.
     
  16. JThomas7

    JThomas7 Well-Known Member

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    Rear bearing was completely gone putting first up against the back of the transmission with an inch of up and down play.
     
  17. JThomas7

    JThomas7 Well-Known Member

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    fixedmaybe.jpg

    Try it again tomorrow.
     
  18. JThomas7

    JThomas7 Well-Known Member

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    No change. if I can get the truck rolling backwards it will go into reverse. It won't go into reverse from a stop.
     
  19. JThomas7

    JThomas7 Well-Known Member

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    I really wish I could find an entire top plate for a 390v. Fork is discontinued and building it up with broze hasn't made a difference.