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SM465 falling out of gear...wtf?

Discussion in 'The Garage' started by Ben B., Sep 4, 2006.

  1. Ben B.

    Ben B. 1/2 ton status

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    My SM465 falls out of third sometimes when you hit a bump or whatever...What's wrong with it?
     
  2. big dan

    big dan 1/2 ton status Premium Member

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    I think it has something to do with the third gear syncro rings. Mine does it every time you let off the gas. From what Ive heard its a common problem with these trannies and is pretty easy to fix. I just havent got around to it.
     
  3. guido666

    guido666 1/2 ton status

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    Easy to fix? How, by rebuilding? Mine pops out of 1st.
     
  4. big dan

    big dan 1/2 ton status Premium Member

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    I think there is a kit you can get. dont remember who from so unless someone else knows Ill have to look it up. I dont think its a full rebuild either but I dont know for sure. a rebuild would prolly fix it though if it needs one.
     
  5. yoshisv

    yoshisv 1/2 ton status

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    I purchaed a kit from www.anaheimgear.com. After the rebuild it was kind of hard to shift, But got better with time. There is no way mine will fall out of third anymore. I beleive the new detent springs on the shifter rails help more than anything since the ones in the kit are stiffer than new stock replacements.
     
  6. readymix

    readymix 3/4 ton status

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    There are 3 possibilities that could be causing your problems. I don;t remember them all off hand but Aneheim can hook you up.

    If it was me I would do a full rebuild. A 465 can be rebuilt in less than one day.
     
  7. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    It is a common misconception that an SM465 falling out of gear is caused by a syncro ring. This is most definitely not the case -- Even if your syncro ring lost all it's teeth, you could still get your transmission shift collar onto a gear, and have it not fall out of gear. Syncros don't do anything but speed up the gear you are attempting to shift into so that the shift collar, and the gear are spinning at the same speed, making it possible to slide the shift collar onto the gear without grinding the splines between the two. That is the sole symptom of a bad syncro -- Grinding into a gear.

    That said, there are three possiblities of what is causing your problem:

    1. Shift Forks

    The shift forks in the SM465 have some sort of a nylon / teflon type of wear pad on them when they are brand new. These pads ride along in the shift collar, and prevent the metal shift fork from grinding against the metal shift collar, creating a ton of wear. They work fantastic, but as they are used, they wear out, and eventually you are down to just metal on metal anyways.

    2. Sloppy Shifter

    If your shifter is really sloppy, then you will not be able to move the the shift forks through their full path, which again will cause the shift collar to not slide all the way onto the gear's splines. There are a few things that can make the shifter sloppy.

    First, and most common is the roll pins at the top of the shifter housing. Often they will break, or loosen up and wriggle out, which creates a significant amount of slack in the joint between the shifter and the housing.

    Second is the joint that the roll pins retain. The shifter rotates on the semi-circular joint which often breaks off the shaft due to rather weak spot welds from the factory. If you can see any cracks in the weld, you need to either re-weld it yourself, or have someone else weld it if you arn't confident of your welding abilities.

    Third is a pair of O-rings on the shifter, which are suppost to be located under the sleeve that the shifter joint sits above. They usually disintergrate, and dissapear, which creates more slack, and causes more metal to metal wear. Sometimes a newer shifter has one big solid bushing hot injected into it, which replaces the o-rings. Take your shifter apart, and you'll know what I mean.

    Finally, the shift rail springs eventually wear out, which can make it easy to get the transmission into a gear position, but also can make it easy for the shifter to fall out of that position if the shift collar pushes back for some reason.

    3. Countershaft Snap Ring

    On the countershaft, there is a gear that is held into place by a snap ring on either side. Aneheim claims that if this snap ring becomes worn, it can allow the gear to walk backwards a touch and throw the gear out. Their solution is a steel sleeve that allows you to remove the snap ring by sliding it between the problem gear, and the next gear that is pressed on.



    Out of these three possibilities, 99% of the time, it will be a combination of possiblity 1 and 2, with 80% of the problem being your shift forks. Unfortunately, the shift forks arn't easy to find in good shape used anymore, and are fairly expensive new. You can't just replace the little contact pad either. The o-rings, and snap rings are cheap and easy to replace, but you need to make sure you get the correct sizes, so its best to buy from Aneheim. The shift rail springs are a bit more complicated, but still arn't half bad.

    I personally believe that the third possiblity is a bit of a farce. If you've got proper shift collar engagement, a countershaft gear walking around shouldn't do anything but make some gear whine. It won't make the mainshaft gear move, which is the gear that the shift collar engages to. My old 74 SM465 had several hundred thousand miles on it, and while the shift forks, and shifter were all replaced prior to myself purchasing the truck, I know it didn't have a sleeve on the countershaft, and it never once fell out of gear. My 80's 4x4 SM465 has one in it, but that is just becuase the donor 2wd transmission I picked up had one, and I felt there was no reason why not to put it in if I had one available to me.

    These transmissions are basically bullet proof. If you keep lube in them, they will outlast 4 - 5 truck drivetrains without any attention below the shift forks. With possibilities 1 and 2, you don't have to do any more than shift the transmission about half way into reverse, then undo the bolts holding the top of the transmission on, and lift it off. You then have everything that may have a problem in your hand.

    If you go ahead and buy new shift forks, and fix the cause of the sloppy shifter, you can have that transmission shifting like it came off the showroom floor the day before for only $150 or so. It will also be good for another 20 years before you need to even think about it again. Try and get that kind of reliability / ease & affordablility of rebuild from an automatic!

    Also, don't drive around with your hand on the shifter, this just presses the contact pad on the forks against the rotating shift collar, which causes it to wear out prematurely. Shift the truck into gear, and let go of the shifter.
     
  8. MoonMan

    MoonMan Registered Member

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    Having rebuilt these transmissions before, I completely agree with SerriaClassic.
     
  9. big dan

    big dan 1/2 ton status Premium Member

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    great info, I just learned something new.:D
     
  10. guido666

    guido666 1/2 ton status

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    Thanks for all the awesome info.
     
  11. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    No problem!

    Don't worry, I learn new stuff every day too :D I thought it was the syncros until I rebuilt mine, and saw with my own eyes how that couldn't be possible :)
     
  12. Ben B.

    Ben B. 1/2 ton status

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    GREAT post SierraClassic.
     
  13. Chevy305

    Chevy305 6 Lug 14bsf Status Premium Member GMOTM Winner

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    Wow! Very nice! ;)
     
  14. Ben B.

    Ben B. 1/2 ton status

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    Hell, anyone for sticky of that post?
     
  15. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Better do some spell checking / grammar work first :eek1: Wrote that up shortly before midnight and my thoughts can get a bit scrambled, lol
     
  16. lamberthkp

    lamberthkp SITFU Premium Member

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    well at least it aint like my 465 i get stuck in 3rd gear out on the road and have to set there and play around with the shifter 15min to an hour before i can get going again, it happens about every 2 weeks . :D
     
  17. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Get a new shifter, and it won't happen again :P

    The shifter is suppost to have a bit of a bulge at the bottom so it doens't fit between the shift fork rails like it happening to you
     
  18. lamberthkp

    lamberthkp SITFU Premium Member

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    would that work? :D it was jumping out of 3rd but after it got stuck it has'nt came out of gear again, it seems to get stuck when dont do a good sqaure shift from 2nd to 3rd. :D
     
  19. Goose

    Goose 1/2 ton status

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    In my old '77 my shifter got stuck once.
    I stopped and rocked the truck back and forth and it freed it up.
     
  20. lamberthkp

    lamberthkp SITFU Premium Member

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    when mine gets stuck it sticks in 3rd but not in 3rd, like it does not make it all the way in the gear, some time when it does it i can push really hard on the shifter and it will go on into gear and then the tranny will work fine after that.. for a little while
     

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