Bicycle Mechanics - Mysterious hub issue

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Aquakitty
10-23-10, 01:52 PM
The hub is Shimano m525 Deore rear freehub.

I was going down a big hill the other day when suddenly my rear disc brakes locked up and I laid a big line down the road, fortunately I was not going very fast. On inspection it looked like the wheel twisted. This was bizarre to me since I am always very careful to super tighten my quick release.

So when I got it home I removed the wheel and the hub seemed completely seized. On the drive side I noticed the hub lockring was loose and hand turnable.

Upon removing the axle everything was fine. Bearings well grease and clean, axle straight..so as far as I can tell the hub seized only because the cone nuts tightened themselves! Since purchasing the bike/wheels I have never messed with the hub aside from testing it for sloppiness.. is it even possible for the cone nuts to work their way in so far the wheel locks and twists?

This could explain why my last bike ride was so darn tough, I felt like my bike was dragging... at the time I just assumed it was my lazy ass, but it probably was the bike!

Any idea what could cause this or how to prevent it? First time I ever ran into something like this. FTR I have been loading the rear with weights to test the bike for a touring load, but the time this happened the bike was unloaded.

DannoXYZ
10-23-10, 02:10 PM
Tighten the locknut to cone... on both sides.
davidad
10-23-10, 04:55 PM
When ever you work on a hub the right side cones should be very tight else they close up and ruin the hub. Make the final adjustments with the left cone and locknut. There should be a small amount of play that will go away when the quick release is closed and compresses the hollow axle.
A friend lost his rear hub when the thing came out of adjustment and ate the cups.

duckforcover
10-23-10, 08:08 PM
It is possible for the cones to loosen and cause this lockup...rare, but several conditions may have contributed.


I was going down a big hill the other day when suddenly my rear disc brakes locked up

Heat and also, some disc brake setups tend to pull the hub to one side or the other under heavy braking, and long downhills the heat goes right into the hub.


...always careful to super tighten my quick release.
This... tight is good, but doing it consistently every time is also important because the way you close your QR, also changes the bearing adjustment. The loose bearings need a little room to expand, lube, clean and cool themselves.

All related to heat...



On the drive side I noticed the hub lockring was loose and hand turnable.

heat.


.so as far as I can tell the hub seized only because the cone nuts tightened themselves!

heat.




Any idea what could cause this or how to prevent it?

well, there are no guarantees in life but I tried to point out some possible causes. Also, experienced mechanics generally have a tried and true order of adjustment and final tightening that they follow to minimize these things... I would definitely replace the loose bearings, fresh grease, and have the cones checked out for damage. Check the disc caliper positioning and pad adjustment as well, if applicable.

Also, I want to commend you for a very clear and concise post of what happened.