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MTB: Wheel and disc brake wobble
#1
Hi,

[Please skip to the text in bold at the end if you don't want the background Smile ]

The disc brakes on my Trek Remedy 2013 (Shimano XT 180mm) have always squealed, especially the front disc and at the start of a ride. I think this is because I didn't bed them in properly when I first got the bike - I didn't even know I had to bed then in.

A few weeks ago, I had a nasty fall, running of the trail into some grass, then (possibly hitting something) flipping over the handle bars before landing back on the trail and sliding on my back. I thought the bike had come off relatively unscathed, but last weekend on my first ride since the crash, the rear brake was practically useless and both brakes were embarrassingly loud.

I followed the Tech Tuesday - Silence That Squeaky Disc Brake guide. When putting the bike back together, the rear wheel is fine, but the front wheel isn't - the disc brake is catching when spinning. The disc wobbles between the pads and catches at certain points.

I removed the disc and it lay flat on the table so I'm sure it's not bent. I then reattached the disc, tightening the bolts in the correct order, using a torque wrench, but it still wobbles. Then I noticed that when the wheel spins, the wheel itself wobbles very slightly, it's difficult to be sure, but I think both the wheel and the disc wobble is in sync.

Can someone please advise what would cause both the wheel and the disc brake to wobble? Everything I have found so far just tells me to remove and reattach the wheel (QR), but that seems to make no difference. There is no visible damage to the axle, could there be something wrong with the hub?

Cheers,

Charlie
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#2
Charlie; wheel bearings; they need to be repacked if you have cup and cone; replaced if you have cartridge bearings.
Nigel
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#3
Hi Nigel, thanks for the quick reply. As I've new to all this, I've just googled the difference between the two, but still not sure which ones I have...

According to the Trek bike specs, my wheels are Bontrager Rhythm Elite with 15mm front hub. From the Bontrager website it says they have Sealed bearing hubs with 3 pawl, 24 tooth drive mechanism for quick engagement and durability. As it says sealed, does that mean they are the cartridge bearing type?
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#4
(09-04-2013, 03:52 AM)jo3yp Wrote:  ........ As it says sealed, does that mean they are the cartridge bearing type?

Probably; I am not familiar with the hubs, and the website is somewhat lacking in technical details.

Cartridge bearing hubs are easy to work on - if you know what you are doing - and can be turned to scrap in seconds if you don't. Take it slow, and look at http://bicycletutor.com/check-bearing-wear/ unfortunately, Alex doesn't have anything yet on changing out cartridge bearings. There are probably some videos on youtube.

You will need new bearings.

Please note that sealed, does not really mean sealed; it is pretty easy to get water in there, and trash the bearings. Cyclocross people, pop the seals off cartridge bearings, and stuff them full of grease - boat trailer wheel bearing grease is good as it stays in place even under water. Cartridge bearings come with enough grease to last decades if the water and solvents are kept away from them. But that can easily be reduced to less than a day.
Nigel
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#5
(09-04-2013, 04:29 AM)nfmisso Wrote:  You will need new bearings.

Please note that sealed, does not really mean sealed; it is pretty easy to get water in there, and trash the bearings. Cyclocross people, pop the seals off cartridge bearings, and stuff them full of grease - boat trailer wheel bearing grease is good as it stays in place even under water. Cartridge bearings come with enough grease to last decades if the water and solvents are kept away from them. But that can easily be reduced to less than a day.

OK, as I probably need new bearings, I will take the bike down to the local Trek store and get them to take a look.

As you have mentioned water can get passed the seal, it's possible that my friend got a little too close with the power wash after a ride. I have to clean the bike after riding a certain trail so I can get it back into a taxi and the power wash is the only way, but I always aim for a light spray and try not to go anywhere near the bearings. I will make sure I'm the only one who cleans the bike in future.

Thanks for your help and advice, much appreciated.

Cheers,

Charlie
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#6
It turned out that both the wheel and the disc were bent, the bearings were fine - it was just a coincidence that the wobble was in sync.

The guy at Treknology straightened both out, fixed my rear hanger which was also way out of shape and also tightened up pretty much the whole bike. I guess the fall did a lot more damage than I thought!
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