Help Mechanical disk brakes

luka

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Jan 13, 2015
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#1
My new bike has mechanical disk brakes BR-R51. Since the "calipers" remain attached to the frame and the disks to the wheel axis, the brake cable has to be detached any time the wheel is removed. The guy at the shop advised me not to take the wheels off before I learned how to adjust the brakes, a process he assured me was not easy. He took 5 minutes or more just to adjust the front brake lever to my liking, as it was too lose. Several weeks after I bought the bike, I still haven't had to take the wheel off or set up the brakes, but any flat or boarding a train etc. will require this sooner or later. So I'd like to ask if anyone else has experience with mechanical disk brakes. I am not convinced they are so hard to take care of, but I'm not 100% confident either. Here is what it looks like:




And here is the Shimano manual covering this model:
 

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George5

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Oct 16, 2014
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#2
Since the "calipers" remain attached to the frame and the disks to the wheel axis, the brake cable has to be detached any time the wheel is removed.
I think you have this wrong. You don't need to touch the cable at all. Try it and it should work. If you can extract the wheel then it will fit back in. If you couldn't fit it back in the wheel wouldn't normally turn without friction. Is this your first road bike?
 
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luka

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Jan 13, 2015
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#5
OK, another question remotely related only because it is mounted on the same bike. What's with the elongated rear mech? I've taken it a bit off road and it's picked up all sorts of stuff in the RD, pulleys etc. Why do they make it closer to the ground? It just seems counter-intuitive...
 

leicaman

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Sep 20, 2012
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#6
Are you sure that either your Japanese or his English weren't quite up to scratch here? The most stupid of stupid bike shop workers wouldn't think you have to remove the cable each time you take the wheel off.
The only problem with disc brakes when taking a whee off is when they are hydraulic brakes. In that situation , you need to put a spacer between the brake pads in case the lever is pulled.
 
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TCC

Tokyo Cycling Club
Jun 30, 2013
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#7
Longer cage allows for a larger range in the gears, ie., you can use a cassette on the back with a massive cog going down to a tiny cog. Short cage mechs have a limit to the size of the biggest cog, and also the range of gears they can use.
 
May 22, 2007
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halffastcycling.com
#8
What's with the elongated rear mech? I've taken it a bit off road and it's picked up all sorts of stuff in the RD, pulleys etc. Why do they make it closer to the ground? It just seems counter-intuitive...
A longer derailleur cage than you are used to on a road bike would be because the bikes's gearing has a larger chain capacity than a road bike.

That, and the disk brakes, lead me to think that what you've got there is a cyclocross bike.

See "Capacity" here http://www.sheldonbrown.com/gloss_ca-g.html
 

TCC

Tokyo Cycling Club
Jun 30, 2013
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#9
The most stupid of stupid bike shop workers wouldn't think you have to remove the cable each time you take the wheel off.
I have seen people working in bike shops who couldn't figure out how to release V-brakes and undid the allen bolt, and loosened the cable that way, to get the wheel off. There are some extremely dumb people out there.
 

George5

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#10
it has a wide range of gears so it needs a larger capacity rear cage to take up the slack in the chain when you are running the smallest chainring. Same as mountain bike derailers.
Maybe the guy in the shop was talking about every time you change the pads? In which case he would be right.

what mike said.
 
May 22, 2007
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#11
I have those same brakes on my CX bike. I took the front wheel off today (to go in the car) and slotted it back on without a second thought.

Users of hydraulic disk brakes may place a spacer between the pads when the wheel is off the bike, to prevent the pistons from being expelled if the brake lever is accidentally compressed. But this doesn't affect you and in any case does not affect replacement of the wheel save that the spacer should be removed first,
 

luka

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Jan 13, 2015
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#12
That, and the disk brakes, lead me to think that what you've got there is a cyclocross bike.
Yes, of course it is cyclocross, though I perhaps forgot to mention that in this thread.

it has a wide range of gears so it needs a larger capacity rear cage to take up the slack in the chain when you are running the smallest chainring.
Well I've got 46-36 at the front, and 11-28 at the back, which is not much wider than on the road bike... I wish it had a triple chainring though.

Longer cage allows for a larger range in the gears, ie., you can use a cassette on the back with a massive cog going down to a tiny cog.
OK, this explained it very precisely. So I COULD put such a cassette, though it came equipped with pretty much standard road one. OK, got it.

Are you sure that either your Japanese or his English weren't quite up to scratch here?
Rest assured it wasn't a language problem. When I think about it now, he was more like I might need to reset the brake setup because when wheel is replaced the disk may not be perfectly alined and may rub against the pads. Then because I wanted the lever feeling fixed, he sorta demonstrated what needs to be done, and I may have mistakenly inferred that this is something that must be done every time. It was probably more of a warning that it MIGHT sometime happen. In any case, I don't feel he was giving me complete answers, but it may be because he wants me to bring it in for servicing rather than fixing it on my own.

I have those same brakes on my CX bike. I took the front wheel off today (to go in the car) and slotted it back on without a second thought.
Now this is encouraging. I'll go for another off road ride in the morning, and will take the wheels off to wash it later. @Half-Fast Mike will get invoiced if anything goes badly. :p You had a great ride today. Too bad I live too far north to join. Anyway, I will be on the lookout for rides that might incorporate some off road segments (perhaps the one on Mt Fuji you mentioned might be good).
 

timefleas

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Nov 30, 2013
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#13
Most of your questions have been answered, and you have correctly assumed the rest. I find disk brake set ups slightly less forgiving than rim brakes, so when a wheel is off to fix a flat or whatever, it might go back on a hair off from the way it was set before--usually just resetting the wheel will get it right, but sometimes a bit of fiddling with the brake mount might be necessary. There is no problem whatsoever in removing a wheel, with the caveat about hydraulic brakes in mind of course--nothing you need to worry about with your brakes. Over time you will need to adjust pad to disk distance, and eventually replace the pads, all pretty easy to do. (I personally don't like disk brakes, even though they are smooth and solid, so I took them all off my MTBs that were equipped with them, and replaced them with canti-brakes--most frames won't even give you the option these days though, and it is nearly impossible to find "clincher" rims for MTBs, but I love the simplicity of rim brakes.)
 

Gunjira

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Oct 2, 2009
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#14
Nothing to add here. Have mechanical dick breaks and take the wheels off all the time. Might have to redo it sometimes, but even if they make some noise it usually does not amount to measurable drag, so can get you home. If it really bothers you, don't loosen up the cable, but instead the two mounting bolts and reset the brake position.
 

zenbiker

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#15
But surely, if you seat the wheel correctly in the dropouts when setting up the disc, all you need to do after removing the wheel is to seat the wheel correctly!
Same as a motorcycle?
 

AlanW

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#16
Unless you have through-axles (which most MTBs do but most road bikes do not) here is a chance that the axle will not sit in absolutely the same position when you re-fit the wheels. OR the QR lever tension might be a little different. And as the tolerances between the pads and the rotor are tight, it's possible to get a little rotor rub. I had a set of Hayes that were a nightmare for this. Most of the time the wheel just slots back in without any issues though.
 
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luka

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Jan 13, 2015
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#17
Thanks everyone, this really helped set my expectations. They guy at the shop was like you don't wanna take the wheels off if you can help it, it can cause all kinds of problems, blah blah. I coundn't ride this morning but will do this evening when it gets a bit cooler, and if the bike gets really dirty, time permitting, I'll have a go at getting one or both wheels off for a wipe down. I now have a reasonable hope they'll fit back alright, without me having to fight my way through the dealer's manual for the brakes. Though the brake adjustment is something I guess I'll have to master sooner or later.