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Disc brake problem
#1
Hi newbie here, I have a problem with the rear disc brake on a 3(?) year old Mongoose Blackcomb. They are mechanical disc brakes and, while I can get the front to lock up, the rear will just barely slow me down. The bike does have to winter outside under a tarp so I fist suspected the cable. Took the cable loose and while it seemed free, I lubed the first 3-4" of cable with an antisieze product, The cable is plastic encased stainless steel and works pretty freely though not as easily as I liked. My next suspect was the brake pads so I removed them and cleaned them with automotive brake cleaner. Not excessively worn. I'm not real certain just how the adjustment knob on the thing works but it doesn't seem to make much difference in the gripping power.

Looking for ideas, my next is move would probably remove the caliper assembly again and roughen the pads with sandpaper, unless some other ideas show up. I may also go ahead and replace the cable but I'm not convinced that will make a significant difference. Attached are pics of the caliper, if anyone can identify the brand I would appreciate that. No marks on the the thing I could find.
Thanks, John

[attachment=3246]
[attachment=3247]
John The problem with experience is I usually don't get it until shortly after I need it.
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#2
The cable looks OK to me, no rust and it isn't frayed. You can try turning the bike upside-down and running some oil along the cable and into the outer, try this at the lever end as well and wherever the inner cable is exposed.

Have you tried the barrel adjuster on the lever?

[Image: barrel_adjust.jpg]
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#3
(06-04-2012, 12:34 AM)xerxes Wrote:  The cable looks OK to me, no rust and it isn't frayed. You can try turning the bike upside-down and running some oil along the cable and into the outer, try this at the lever end as well and wherever the inner cable is exposed.

Have you tried the barrel adjuster on the lever?

[Image: barrel_adjust.jpg]

Hi - Yeah, I took the cable loose at both ends, ran some oil down it and then pulled the inner cable out of the housing as far as it would go in each direction without cutting off the end features and greased the exposed cable with an antisieze compound. Would be about 80mm on each end. Then reassembled everything. I've had the barrel adjuster at both extremes and in the middle.
I'm beginning to think that I may not have enough gripping power in my hands anymore to use this type of brake. I'm 69 yrs old and have tendonitis in my wrists.
Any suggestions welcome, including an alternative brake system that may require less hand pressure. Hydralics maybe??
Thanks, John
John The problem with experience is I usually don't get it until shortly after I need it.
  Reply
#4
Here's some more info on disc brakes and pad types:

http://mikesbikes.com/how-to/disc-brake-basics-pg158.htm

http://www.pinkbike.com/news/brake-pad-information-2009.html

You could try some different pads with a bit more "bite", but I'm not sure what to recommend specifically. I have a set of Avid hydraulic brakes and I'm still using the original pads that came with them, which I assume are Avid made and an organic compound, and I've been quite happy with their stopping power.

I recently serviced a friends bike with cable disc brakes and I have to admit I wasn't overly impressed with their stopping power, it was considerably less than my hydraulic disc brakes and I reckon it was less even than the V-brakes on my other bicycle. I replaced the cables because they were rotten, but no amount of adjustment seemed to improve the initial bite and stopping power, although I didn't try replacing the pads.

The rear brake cable is longer than the front, so with all cable brakes the the longer cable run to the rear makes the rear brake feel more "spongy" than the front brake with a shorter cabe as the cable can stretch more over the greater length.

Having said that, the front brake does most of the work anyway. As you decelerate, your weight is transfered to the front wheel and tyre, increasing its grip, so you can apply more pressure to the front brake before the wheel locks up and you loose traction. Whereas the opposite is true of the rear wheel, as your weight is transfered to the front wheel, so it is reduced on the rear wheel and it will lock up and skid quite easily if you squeeze too hard on the back brake lever.
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#5
(06-04-2012, 12:53 PM)xerxes Wrote:  Having said that, the front brake does most of the work anyway. As you decelerate, your weight is transfered to the front wheel and tyre, increasing its grip, so you can apply more pressure to the front brake before the wheel locks up and you loose traction. Whereas the opposite is true of the rear wheel, as your weight is transfered to the front wheel, so it is reduced on the rear wheel and it will lock up and skid quite easily if you squeeze too hard on the back brake lever.

That's my issue, I cannot lock up the rear, which as you pointed out, should be fairly easy to do. I've found through experience, locking the front is not necessarily the best optionSad I may investigate upgrading the rear to hydralic although, at my age, I don't ride nearly as much as I used to. My current setup, while not optimum, is adequate for normal use. I usally amble along around 15 or 16 km/hr not being in any particular hurry.
Thanks for the responses Smile
John The problem with experience is I usually don't get it until shortly after I need it.
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#6
Like xerxes said, most of the stopping power is in the front, not being able to lock up the back wheel is a non issue as long as using both brakes you stop when you need to. I have old rim type brakes and they are adequate for my needs, just ride and enjoy.

I am not a fan of disc brakes on bicycles, an answer to a non existent problem. Just more ciacikas to sell bicycles.
Never Give Up!!!
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#7
(06-04-2012, 08:50 PM)GeorgeET Wrote:  Like xerxes said, most of the stopping power is in the front, not being able to lock up the back wheel is a non issue as long as using both brakes you stop when you need to. I have old rim type brakes and they are adequate for my needs, just ride and enjoy.

I am not a fan of disc brakes on bicycles, an answer to a non existent problem. Just more ciacikas to sell bicycles.

Hi George - you're probably right. I did feel the disc brakes performed better than the rim in the wet though, at least they did. I have got enough rear brake to control the speed on downslopes so it probably is a non issue. More and more I think it's just my inability to apply as much pressure as I used to, even as late as last year. I have noticed I don't see discs on the rear of later models... this is, of course, a WallyWorld bike.
Thanks again for the response. John
John The problem with experience is I usually don't get it until shortly after I need it.
  Reply
#8
Is there a good bicycle shop, with knowledgeable staff, near by?

If so, it may be worth aksing their opinion, they maybe able to suggest alternative pads and or disc rotors that could give you a bit more braking power. This would be considerably less expensive than replacing the whole braking system with a hydraulic one.
  Reply
#9
(06-05-2012, 12:14 PM)xerxes Wrote:  Is there a good bicycle shop, with knowledgeable staff, near by?

If so, it may be worth aksing their opinion, they maybe able to suggest alternative pads and or disc rotors that could give you a bit more braking power. This would be considerably less expensive than replacing the whole braking system with a hydraulic one.

Hi - Good suggestion. There is a dedicated bicycle shop about 50km up the road. I don't know how knowledgable they are but they do carry some high end bikes. Next time I get up that way I'll stop in and have a chat with them. I'm going to need some cable ferrules anyway as I think I will pull the inner cable completely out of the outter housing and thoroughly clean and lube both. Come to think of it, I believe I'm out of
Tri-flo also and that's likely the only place I'll find some out here.
Thanks again. John
John The problem with experience is I usually don't get it until shortly after I need it.
  Reply
#10
Hey all! Sorry that I'm late to the party. Been working on some disc brakes....

All disc brakes, whether Hydraulic or Cable actuated, require a 'burn-in' period to achieve max performance. During this period, pad material is transfered to the rotor via heat. As the front brake easily gets hotter than the rear due to it being the primary binder, the rear is often neglected. I recommend, to new bike buyers, to find the biggest, baddest, longest downhill and ride the brakes until they get hot enough that the rotors turn colors from the heat. If no hills - just get up some speed and stop quickly, repeatedly. If this isn't done, the pads tend to be burnished by the rotor rather than the pad impregnating material into the porous metal of the rotor. With glazed pads, you'll have minimal stopping power.

Pull the pads from the caliper and scuff up on some 120-180 grit sandpaper. Then boil them in a pot of water and pat dry to remove any residual material or contaminants. Once completely dry, reinstall and do the 'burn-in' described above. Be certain that you get absolutely NO oil, not even oil from your fingertip skin, on the rotors. It will transfer to the pads and we have to start all over!

Here ---> more details.
http://www.parktool.com/blog/repair-help/shimano-r-hydraulic-brake-service-and-adjustment

I like Cold, American beer. Thx! Smile
Wheelies don't pop themselves. (from a QBP fortune cookie)
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#11
(06-11-2012, 09:48 PM)RobAR Wrote:  Hey all! Sorry that I'm late to the party. Been working on some disc brakes....

All disc brakes, whether Hydraulic or Cable actuated, require a 'burn-in' period to achieve max performance. During this period, pad material is transfered to the rotor via heat. As the front brake easily gets hotter than the rear due to it being the primary binder, the rear is often neglected. I recommend, to new bike buyers, to find the biggest, baddest, longest downhill and ride the brakes until they get hot enough that the rotors turn colors from the heat. If no hills - just get up some speed and stop quickly, repeatedly. If this isn't done, the pads tend to be burnished by the rotor rather than the pad impregnating material into the porous metal of the rotor. With glazed pads, you'll have minimal stopping power.

Pull the pads from the caliper and scuff up on some 120-180 grit sandpaper. Then boil them in a pot of water and pat dry to remove any residual material or contaminants. Once completely dry, reinstall and do the 'burn-in' described above. Be certain that you get absolutely NO oil, not even oil from your fingertip skin, on the rotors. It will transfer to the pads and we have to start all over!

Here ---> more details.
http://www.parktool.com/blog/repair-help/shimano-r-hydraulic-brake-service-and-adjustment

I like Cold, American beer. Thx! Smile

Hi Great suggestion!!! I was suspecting glazing but didn't know exactly what to do about it. I did clean the pads with automotive brake cleaner. As far as big, bad hills go, out here in the middle of Kansas???
Will give the sandpaper a shot, can't hurt anything.
John The problem with experience is I usually don't get it until shortly after I need it.
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#12
which disc brake is better?
hydraulic or cable
pattern or circular
big or small
thin or thick
  Reply


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