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Old 12-04-21, 02:36 AM
  #25434  
dirtman
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Originally Posted by 2fat2fly View Post
I had a neighbor bring me a bike yesterday with the rear wheel locked up tight. She said she was riding and all of a sudden the back wheel locked up, then broke free, then locked up again.
The SA AW hub was locked up tight.
As soon as i put the bike up on the stand I could see something really bad happened. There was a dent in the shell from the inside, and the shift cable was pulled out of the shifter up top.
I removed the cable from the indicator, removed the indicator, and removed the axle nuts. That's when I really realized how bad it was. The axle had twisted on the left side only, spreading the dropouts a bit and wedging the round part of the axle in the frame. I had to take a block of wood and drive the axle down out of the dropout on the left side.
I immediately saw that the left axle threads were twisted almost a quarter turn and the axle had 'threaded' the inside of the dropouts.
I then backed off both bearing cones, and both axle bearings and cones were fine.
I then found that the driver was stuck in the hub. It took a brass mallet to knock it loose.
The bearings, race, and driver were stuck together, the bearings that fell out were black and burnt looking. The right side race was blue and the driver had come color as well and a few chunks out of the bearing race.
I pulled the internals and soon found that the pinion gear was loose on the axle, and half the pin that holds it in place was gone. The gears and the rest of the hub were fine except for one broken left side pawl.
The owner is a big woman, 6ft 5in or so in her 60's. The bike is a ladies Sports.
The hub was well oiled, and there was no real grinding or cutting going on, which made me think it did indeed happen pretty fast. However, I didn't find the missing half of the pinion gear pin, or the missing half of the one pawl.
The driver bearings were about half their normal size and not even close to round and there was a lot of grinding dust in with the bearings and not much lube there, but the bearings were pretty much burned black.

The hub shell was re-usable, I replaced the axle, right bearing race, cone, and all the bearings and its back up and riding. The pinion gear was actually fine too, but rather than mess around with the old gear I just found a used axle for it.

Here's the axle



....
The entire axle is twisted, not just the end, look at how far the flats are from each other on the other end. I also thought it odd that the sold end of the axle twisted before the hollow end. Both no-turn washers were also destroyed, with the left one broken in half. Since the dropouts were so chewed up, I added an extra no turn washer on the outside as well on the left side. When i thought about it and what had to happen for this to fail this way I figure that both the driver and the pin or pawl had to lock up the internals at the same time. Otherwise, the locked up driver would have just made it a fixed gear but it was locked up completely. I suppose if it didn't lock up, the axle would have kept turning and just eventually snapped.
I've had a few broken axles and stripped pinion gears but I've not seen one locked up or twisted like that. All of the hubs that had broken axles that I found were badly abused and run till they just wouldn't go any further. The few stripped pinions were in hubs that were badly worn internally, likely run dry for years.
I could imagine what sort of havoc a loose or protruding pin could do when moving along at speed, especially with a heavier rider

As a kid, I broke an axle on a road bike and the rear end locked up while descending a hill, it wasn't a fun experience

I would suppose with a three speed hub, if something broke or locked up at speed, the forces could be amplified even greater than with a straight axle. If the driver locked up, the effect would be simply a fixed gear situation, but if you lost a set of pawls combined with a loose pin or some shrapnel in the mix, the planetary gears could exert some serious force on the axle as various components stopped turning. I wonder if the planetary gears could create a reverse gear situation if one set of pawls were either engaged or not there in the right combination.
Either way I can imagine the crunching and grinding sounds that had to make as it locked up.
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