• 06-03-2009
    w4ta
    Dura-Ace 7801 Cassette Assembly
    After transferring a 11-21 Dura-Ace 10-sp cassette from a Dura-Ace WH-7801-SL to a Dura-Ace WH-7801 wheel, the backward spin of my chainring is a lot less.

    When on the bike-stand, I used to spin my front chainring backwards (with my hand) for about 2 revolutions. Now, when I spin the new wheel backwards, it spins only .5 to .75 of a revolution.

    Is there an obvious reason why it would spin less? I cleaned and reassembled the cassette according to the Shimano tech-document, placing the two black spacers in the correct position.

    My only observation is that while you can only fit the rings onto the freewheel based on proper spline-alignment... the black spacers seemed as if they could be rotated, fitting in any number of alignments.

    (on a casual ride, there were not apparent issues with shifting, noise, or performance... but the lack of spin of my new WH-7801 hub versus my old WH-7801-SL has me concerned. Thx.)
  • 06-03-2009
    SwiftSolo
    Quote:

    Originally Posted by w4ta
    After transferring a 11-21 Dura-Ace 10-sp cassette from a Dura-Ace WH-7801-SL to a Dura-Ace WH-7801 wheel, the backward spin of my chainring is a lot less.

    When on the bike-stand, I used to spin my front chainring backwards (with my hand) for about 2 revolutions. Now, when I spin the new wheel backwards, it spins only .5 to .75 of a revolution.

    Is there an obvious reason why it would spin less? I cleaned and reassembled the cassette according to the Shimano tech-document, placing the two black spacers in the correct position.

    My only observation is that the while you can only fit the rings onto the freewheel based only on proper spline-alignment... the black spacers seemed as if they could be rotated, fitting in any number alignments.

    (on a casual ride, there were not apparent issues with shifting, noise, or performance... but the lack of spin of my new WH-7801 hub versus my old WH-7801-SL has me concerned. Thx.)

    Not certain I understand. You should be able to spin your cranks backwards as many revs as you want. What stops you? Does the chain come off the front chainrings or does the freehub somehow lock up?
  • 06-03-2009
    w4ta
    Quote:

    Originally Posted by SwiftSolo
    Not certain I understand. You should be able to spin your cranks backwards as many revs as you want. What stops you? Does the chain come off the front chainrings or does the freehub somehow lock up?

    Thought I might not have been clear on that.

    When the bike is on the stand, and when I spin the crank hard and let go... it used to spin about two revolutions on its own before slowing to a stop. Now, when applying equal force and spinning the crank backward and letting go, it seems to halt abruptly by comparison... spinning only about 1/2 or 3/4 of a revolution on its own.

    The hubs/freewheels are both Dura-Ace WH-7801 series (the wheelsets changed from WH-7801-SL to WH-7801).

    Hope that clarifies the concern. Thanks-
  • 06-03-2009
    SwiftSolo
    Quote:

    Originally Posted by w4ta
    Thought I might not have been clear on that.

    When the bike is on the stand, and when I spin the crank hard and let go... it used to spin about two revolutions on its own before slowing to a stop. Now, when applying equal force and spinning the crank backward and letting go, it seems to halt abruptly by comparison... spinning only about 1/2 or 3/4 of a revolution on its own.

    The hubs/freewheels are both Dura-Ace WH-7801 series (the wheelsets changed from WH-7801-SL to WH-7801).

    Hope that clarifies the concern. Thanks-

    It is friction in the freehub that causes the cranks to keep turning. I'd guess that your new freehub is cleaner (internally) and therefore has less friction.
  • 06-03-2009
    fast ferd
    Does it need the spacer, perhaps?
  • 06-03-2009
    w4ta
    Quote:

    Originally Posted by SwiftSolo
    It is friction in the freehub that causes the cranks to keep turning. I'd guess that your new freehub is cleaner (internally) and therefore has less friction.

    Actually, it's the newer freehub that spins less... and by all external appearances, the hub and freewheel parts appear clean. The newer wheel has very few miles on it... yet the freewheel doesn't spin as freely.

    There's no problem with wheel spin. Maybe this isn't a problem... but I'm thinking if the there is less rotation when spinning the crank... perhaps there is friction that will affect performance when riding. Thx
  • 06-03-2009
    fast ferd
    Okay, I will make this a little more obvious, since you did not consider my suggestion. There is a thin washer/spacer that comes with your 7800 cassette. You may need to mount this on the freehub body PRIOR TO installing the cassette. Otherwise, the cassette carrier could chafe against the hub.

    I could be wrong, but this seems the likely culprit. Can you address this idea?
  • 06-03-2009
    suprcivic
    there is a good possibility that the springs that push the pawls into the freehub body are stiffer since they are new and therefore create more friction. this would slow down the spin of your cranks.
  • 06-03-2009
    w4ta
    Quote:

    Originally Posted by fast ferd
    Okay, I will make this a little more obvious, since you did not consider my suggestion. There is a thin washer/spacer that comes with your 7800 cassette. You may need to mount this on the freehub body PRIOR TO installing the cassette. Otherwise, the cassette carrier could chafe against the hub.

    I could be wrong, but this seems the likely culprit. Can you address this idea?


    Thanks- I'll evaluate when I return from work this evening. However, I'm thinking this is not the problem... as I recall from the Shimano instructions, the spacer is not needed on a 10-speed cassette when affixed to a 7801 hub/freewheel (which this is).

    Thx.
  • 06-03-2009
    w4ta
    Quote:

    Originally Posted by suprcivic
    there is a good possibility that the springs that push the pawls into the freehub body are stiffer since they are new and therefore create more friction. this would slow down the spin of your cranks.

    Thanks-

    I'll put it through some moves when I get home this evening and try to discern if there is actually any rolling resistance or performance deficiency. Right now, I've only noticed that the freewheel doesn't spin as freely when up on the bike stand... could be meaningless to actual performance on the road (if the springs or internals are tighter due to newness...).

    Many thanks for the replies-
  • 06-03-2009
    wim
    Most likely, you're just seeing the indications of a tight-running new versus free-runnig older freehub. As metal parts bed in and seals loosen up, your crank-spinning test will show its normal results again. BTW, that test just simulates coasting, so it's no indicator of fast-riding performance.
  • 06-03-2009
    Dr_John
    Quote:

    There is a thin washer/spacer that comes with your 7800 cassette. You may need to mount this on the freehub body PRIOR TO installing the cassette.
    The 7801 hubs are ten-speed only.

    Do not use a spacer. The spacer is for use with 8,9,10 speed compatible hubs, such as the 7850 hubs.

    Quote:

    could be meaningless to actual performance on the road (if the springs or internals are tighter due to newness...).
    :thumbsup: Don't worry about it unless you pedal backwards a lot. :) Check after a few 100 miles.
  • 06-04-2009
    w4ta
    Thanks for the replies. Took the bike out on a vigorous ride this morning and it performed perfectly. So, despite the freehub spinning a lot less than my previous one, it does not appear to have any performance defects.

    No spacers were necessary (as it is a 10-speed). As some suggested, it might be tighter due to newness...

    Anyway, thanks again for your replies...