What happened to 5th gear????

Discussion in 'Airheads' started by ironjack63, Mar 6, 2013.

  1. ironjack63

    ironjack63 Adventurer

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    I finally got my '81 r100rt started today and took it on it's maiden voyage after sitting in my buddie's storage barn for 7 years. It needs more tweaking and probably needs the valves set tomorrow, but my problem is that on my 25 mile ride today I could not get the bike to shift into 5th gear. No grinding, no nothing. I found a neutral between 4th and 5th, but no 5th gear. All shifts between the first 4 up or down were pretty darn smooth for a 32 year old bike, but no 5th gear. Any ideas?
    #1
  2. Rob Farmer

    Rob Farmer Long timer

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    Has it any whining in the other gears?

    First thing to check - is it a smooth gearbox or does it have reinforcing webs?
    #2
  3. AntonLargiader

    AntonLargiader Long timer

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    Are you sure the shift lever isn't hitting anything, or that the shift linkage is loose? Losing 5th is just about unheard of on that transmission.
    #3
  4. DaveBall

    DaveBall Long timer

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    Are you certain it is the original gearbox? Somebody may have swapped in a 4 speed. Why they would do that on an RT? I have no idea. But it could have been done.
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  5. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Continuing to grab at straws, the gearshift pattern is one down and four up-- you couldn't be skipping 1st gear?

    Loose or binding shift linkage is the best idea,

    (yeah, I know the shift pattern has been standardized for centuries now, but I remember the first question in the 60's when "swapping out" bikes was "what is the shift pattern?")

    --Bill
    #5
  6. kixtand

    kixtand Long timer

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    Had this happen on a 5 speed of unknown origin before, turned out that the shift fork was stuck on the shaft it rides on...
    #6
  7. disston

    disston ShadeTreeExpert

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    My money is on the 4 speed trannie being in a bike that should have a 5 speed. But only because it would be the most face palm worthy solution. All the other ideas are also still in the running I guess. Will we hear the solution today?
    #7
  8. ironjack63

    ironjack63 Adventurer

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    I don't believe it is a 4 speed tranny, because when I attempt to shift into 5th gear, all I get is a neutral between gears like the pawl or whatever is just short of engaging. I will look this afternoon for anything in the way of the lever, but I don't recall anything being there. The tranny is not as smooth as my new Bonneville, but it is not bad for a 32 year old bike. There is no grinding or whirring or any out of place sound to be heard going down the road, it just won't shift into 5th. More to come after another test ride.
    #8
  9. dm635

    dm635 I Roll

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    I get some very intermittent false neutrals between 4th & 5th. Doesn't happen in the other gears. But usually all gears slip right in.
    #9
  10. Airhead Wrangler

    Airhead Wrangler Long timer

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    I just took a trashed trans in trade for showing a traveler passing through town how to check/adjust valves, rebuild his carbs, etc. Aside from being really tough to turn over by hand and making nasty growling sounds when you do, it's lost 5th gear. Why are the early 80s boxes less likely to lose 5th?
    #10
  11. 100RT

    100RT Long timer

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    Let's start at the beginning, Was that the first time you have ever ridden the bike? Did it ever have a 5th gear?
    #11
  12. DaveBall

    DaveBall Long timer

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    In my experience, I have not heard of nor found any airhead to lose 5th gear all by itself. Maybe in conjunction with all other gears being blown out a hole in the tranny, but otherwise?

    Start at the beginning. Are you shifting 1 down and 4 up? If so, and you can't get into 5th, then check how you are shifting. These are tractor style transmissions. They can be hard to shift, until you get used to them. Shifting from 4th to 5th can be notchy, especially if the tranny has been abused in it's lifetime. When you are about to shift from 4th to 5th, put a little preload on the shifter prior to pulling in the clutch, then when you pull the clutch, give the shifter a good solid movement upwards.

    If you still can't get it to go to 5th, check the tranny to see if somebody has swapped out the 5 speed for an older 4 speed. It is a fairly simple swap that somebody may have done due to blowing the original tranny, and never got around to putting in the correct one. I have heard of the odd, and very well used, 4 speed tranny having a false neutral above 4th. But that was a very abused bike.
    #12
  13. Kt-88

    Kt-88 I like everything.

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    My r90 did this when I first started riding it. After three fluid changes and a lot of riding it anyway, fifth came back.

    It also used to get stuck in third. No up or downshifting possible.
    #13
  14. 100RT

    100RT Long timer

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    The 81 was the first year for the new style "clutch carrier (flywheel) that includes a different clutch disc, input shaft and all related parts.

    In my opinion, I wouldnt refer to it as a simple swap of parts.
    #14
  15. disston

    disston ShadeTreeExpert

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    Good point RT. As profound an explanation as the older trans swap might be it is not a simple thing to do. Possible 4 speed trans very unlikely.

    As KT's example suggests there is a possibility of things correcting them selves. Have you changed the gear oil in this trans? Would like to see what the stuff in there looks like. Certainly the bike can be ridden at highway speeds in 4th gear.
    #15
  16. ironjack63

    ironjack63 Adventurer

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    I think all this bike needed was some regular running. On today's ride, 5th gear was suddenly there. I can't explain it, but after it shifted into 5th for the first time since I have owned it, it easily shifted into fifth every time after. I don't have a clue what might have prevented it from doing so previously, but I have to believe that sitting idle for 7 years probably did not help. So, long story short, I now have the 5th gear I was so desperately looking for over the last few days.
    #16
  17. robtg

    robtg Been here awhile

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    Probably rust from moisture on the 5th gear shift fork shaft finally wore away.
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  18. AntonLargiader

    AntonLargiader Long timer

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    You tell us! Should be interesting; I've never seen it. In order to lose it because of an output shaft problem, you have to REALLY trash the box. I've trashed one pretty badly that way, limped home with one or two gears, but didn't actually lose 5th. It was just very loud.

    In order to disengage 5th due to the output shaft moving forward, you'd be engaging 1st without trying. That would grenade the transmission (saw this recently on an R1200GS trans).

    Goes without saying that I don't see why the later ones would be less prone to it. I don't think any of them are prone to it at all.
    #18
  19. supershaft

    supershaft because I can

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    I think all of them up to around '86 (?) are prone to a small degree of losing fifth but when they do they loose all the gears at once. I have read people here calling it fifth gear going out. I have seen it numerous times but I don't call it fifth gear going out. I call it the input shaft cush drive going out. I have seen the input shaft cush drive break way more times than I have the driveshaft cush drive (if I don't include the rubber ones!). In the cases I have seen, it was pretty obvious that the cush cam broke and that is what caused the gear to go. BMW was well aware of this issue since in around '86 I think they substantially beefed up the input shaft cush drive. I have never seen one of the beefed up ones break. Maybe that is how the later trannys are less likely to have fifth go out?
    #19
  20. Kt-88

    Kt-88 I like everything.

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    Change your fluid, good sir. I'm happy riding was the answer for you as well.
    #20