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06-16-12, 01:33 PM
Found something interesting yesterday while doing some pre-race tuning on a friend's mountain bike. It has a front Shimano Deore (6 bolt) disc hub. He bought the bike new from the local shop maybe 6 months ago and has put fairly regular miles on it since it was new.
Pulling the front wheel off, I noticed that there was a washer loose on the skewer. "Stange" I thought, and I then noticed that there was more. It appears that the newer shimano axles are only threaded as far as they need to be, allowing the "nubs" to be smooth where they rest in the fork's dropouts. First of all, the locknuts were loose to my hand, not locked at all to the cones, on BOTH SIDES. This likely lead to the cone tightening with use and causing the bearing friction from too much bearing preload.
On the left hand side, the locknut was directly next to the cone. This differed from the right side (non disc side) where there was a *familiar washer sandwiched between the cone and the locknut. The same type of washer that was on the opposite end, floating on the skewer. So the washer that had begun it's life between the cone and locknut had been removed and placed 'outside' of the locknut for some reason. The spacing ended up the same, but instead of the textured locknut being in contact with the dropout face when installed, it was against a smooth washer, that was then against the dropout face...not exactly the most secure looking configuration.
In trying to replace it, I quickly realized the reason that it had been removed. With that washer installed, there wasn't enough threading on the axle to thread the locknut in place. And with the washer on the outside, the spacing (and wheel dishing) were in their appropriate positions, but the "nub" of axle was significantly shorter than the opposing side of the axle. It looked like the axle was just simply too short, by 2-3 mm, leaving the threaded section of the axle too short by the same distance too.
Trying to leave that washer out completely resulted in lock nut spacing narrower than the fork, and when I tried to adjust the brake caliper to accommodate the new spacing, the needed adjustment was outside the range of the caliper...so it wasn't happening. The spacing required the washer's added thickness, but the only way to add it was to have it the way I'd found it, on the outside of the locknut, and diminishing the available dropout contact on that end of the axle.
SO TO MY QUESTION...
Am I missing something here? Could I be overlooking something that's going to allow this to all go together as designed, with the washer sandwiched between cone and locknut where it belongs? Or is it possible that they built the hub with a short axle, and during assembly of the bike simply moved the washer to the outside to 'make it work?' One thing that I neglected to do before sending it off with him was to measure the fork's dropout distance to make sure that it was 100mm. If for some reason it's wider than 100mm, and the actual locknut spacing on the hub is correct WITHOUT the washer, than it may not be a hub problem, just a strange design involving asymmetrical washer spacing on the ends of the hub. But I don't think that's the case. Everything indicated that everything was in line except the axle length. Spacing, Dish and caliper alignment were all perfect with the washer where I'd found it.
Of course I adjusted and tightened both locknuts down (remember they had both been completely loose), but this final issue seems very wrong to me, and I like to follow up on stuff that I don't understand, especially when it's someone else's bike I'm working on. Any input would be appreciated. Thanks. :thumb:
-Jeremy
Pulling the front wheel off, I noticed that there was a washer loose on the skewer. "Stange" I thought, and I then noticed that there was more. It appears that the newer shimano axles are only threaded as far as they need to be, allowing the "nubs" to be smooth where they rest in the fork's dropouts. First of all, the locknuts were loose to my hand, not locked at all to the cones, on BOTH SIDES. This likely lead to the cone tightening with use and causing the bearing friction from too much bearing preload.
On the left hand side, the locknut was directly next to the cone. This differed from the right side (non disc side) where there was a *familiar washer sandwiched between the cone and the locknut. The same type of washer that was on the opposite end, floating on the skewer. So the washer that had begun it's life between the cone and locknut had been removed and placed 'outside' of the locknut for some reason. The spacing ended up the same, but instead of the textured locknut being in contact with the dropout face when installed, it was against a smooth washer, that was then against the dropout face...not exactly the most secure looking configuration.
In trying to replace it, I quickly realized the reason that it had been removed. With that washer installed, there wasn't enough threading on the axle to thread the locknut in place. And with the washer on the outside, the spacing (and wheel dishing) were in their appropriate positions, but the "nub" of axle was significantly shorter than the opposing side of the axle. It looked like the axle was just simply too short, by 2-3 mm, leaving the threaded section of the axle too short by the same distance too.
Trying to leave that washer out completely resulted in lock nut spacing narrower than the fork, and when I tried to adjust the brake caliper to accommodate the new spacing, the needed adjustment was outside the range of the caliper...so it wasn't happening. The spacing required the washer's added thickness, but the only way to add it was to have it the way I'd found it, on the outside of the locknut, and diminishing the available dropout contact on that end of the axle.
SO TO MY QUESTION...
Am I missing something here? Could I be overlooking something that's going to allow this to all go together as designed, with the washer sandwiched between cone and locknut where it belongs? Or is it possible that they built the hub with a short axle, and during assembly of the bike simply moved the washer to the outside to 'make it work?' One thing that I neglected to do before sending it off with him was to measure the fork's dropout distance to make sure that it was 100mm. If for some reason it's wider than 100mm, and the actual locknut spacing on the hub is correct WITHOUT the washer, than it may not be a hub problem, just a strange design involving asymmetrical washer spacing on the ends of the hub. But I don't think that's the case. Everything indicated that everything was in line except the axle length. Spacing, Dish and caliper alignment were all perfect with the washer where I'd found it.
Of course I adjusted and tightened both locknuts down (remember they had both been completely loose), but this final issue seems very wrong to me, and I like to follow up on stuff that I don't understand, especially when it's someone else's bike I'm working on. Any input would be appreciated. Thanks. :thumb:
-Jeremy