[Tgo]

My wife recently inherited a Mountain Bike from her "now headed to college" cousin and I had a bit of an itch of take apart and reassemble something mechanical and manageable. Since the last couple of days I have started taking apart and rebuilding each component in order to service it and learn how it works.

Little background:
The first thing that fascinated me on bicycles were the brakes. It may be due to the fact that, I as a kid used to run out of brake pads (old rim type) every two months, doing long skids, longer than the other kids. Adjusting the brakes weekly so that they work like magic was the only thing 'bicycle maintenance, that I could understand and achieve. To me, its really gripping how knowledge of simple mechanisms enables you to make them work the way you want and in the process learn all their merits and limitations. So it goes, when bicycles started appearing with disc brakes, they were the next frontier for me to fathom. It happened after a gap of 13 years, college, employment and marriage but here it is, laid out in simple terms for everyone interested to understand.

How The Disc Brake Works:

The disc is mounted on the hub and rotates with the wheel. The caliper is mounted on the fork/swing arm and is stationary in rotational terms with respect to a rotating wheel. The mounting of the caliper is in a way that the disc passes through it and in between the brake pads which are housed in the caliper. The caliper has the mechanism which when operated by a cable makes the brake pads inside the caliper move so that they sandwich the disc slowing it down and the wheel as a result slowing the bicycle down.

Mounted on a bike

We all know this and have seen it work marvelously in cars. But the point here is that the disc brakes in bicycles are mostly cable operated rather than being hydraulically operated. This imparts a simple mechanical dimension to these disc brakes which is quite brilliant.

This is a complete breakdown of the components that make up a brake caliper.

The key component at the heart of this is the ball ramp cam. This sketch shows how it transfers the rotational motion from the torque arm into linear motion of the moving brake pad. When viewed from above and anti clockwise motion of the spindle (vertical rectangle) will result in the motion shown by the GIF since the ball is held in place by the groove of the stationary cam.

Cam Mechanism

Please note that the actual installation of the mechanism as per assembly for the brake housing is not depicted in the GIF for simplification of the drawing. In actual assembly the spindle is passing through the stationary cam downwards.

I'll now proceed with assembly of all the components to make a working brake caliper.

Install the stationary cam, Grease the ramps, place the rollers


Installation of the moving cam


Ready for assembly


Seal, spring and foot adjustment screw installed


Pressure foot installed and adjusted with screw


Cable clasping clip installed on lever


Installation of anvil components


Anvil Installation in progress


Mounting bracketry - trick part


Mounting bracket installation in progress


Finished Assembly


The Works - Explained

As the cable operates the torque arm in the direction depicted by Arrow-1 the rotation of the moving cam pushes the pressure foot which pushes the brake pad against the disc depicted by Arrow-2. The very slight play in the bracket mounting bolts/pins allow the caliper to move so that the stationary pad in the anvil which was earlier skimming the disc also grips the disc. A little video of the fully assembled caliper operated by hand is linked below.

https://youtu.be/amcFKhm56SE

[Tgo]

Some points I learned while working on the disc brakes:

• Everything from the Brake Lever to the cam mechanism must be approriately lubricated but the brake pads and disc must not be contaminated with them at all.

• If you forget and spill a bit of oil/grease on the pads and discs you will need to re-surface the pads (sandpaper) or change them altogether depending on the severity of contamination. The discs you can simply clean with dish washing liquid and water.

• Be careful, especially while oiling your chain or greasing your hub bearings as any excess lubricant spilled out may find its way to the brake pads/disc.

• I did not find these cheap generic disc brakes any better than the old rim brakes I was used to as a kid, they are just a novelty item for my kind of use. The good quality hydraulic ones may actually have more benefits.

• Scope for brake adjustment is provided at many places in the system - Brake Lever bracket, Torque Arm, Pressure Foot and Housing mounting bracket. Fiddle around to find your perfect setting.

• Its a good Idea to swap discs front to back before throwing them away completely, based on which one you use more often and effectively.

• Pads and disks are available as replacement parts however any of the internals of the brake caliper/housing/brackets might not be available and you may have to buy the whole assembly either individually or as aset (front & rear)

• Brand of the brakes I worked on (based on markings) were Zoom and Flame courtesy China. But these are pretty generic parts which might be easily interchangeable.

• Brake discs have direction of rotation marked on them so you might want to keep that in mind while installing.

• Most of the cast parts were either Al-Die cast or some sort of sintered metal parts. All the Allen head bolts and screws were made of Steel. While fastening these parts together remember that the steel bolts can very easily strip the threads on the cast parts.Please also avoid use of thread locker/loctite.

• The brakes I worked on seemed to be the simplest in design but weakest in the durability department. Saw a lot of drawings for very expensive alternatives online - these provide compatibility with bigger and better quality brake pads, were lighter in weight, provided more adjustment scope and had a whole bunch of washers in each and every location to ensure longevity and repair-ability.

• My favourite bicycle brakes still are the coaster hub brakes in which on moving the pedals backwards stops the wheel from rotating. No maintenance required and you get clean handlebars.

[Rehaan]

Originally Posted by Tgo

• I did not find these cheap generic disc brakes any better than the old rim brakes I was used to as a kid, they are just a novelty item for my kind of use. The good quality hydraulic ones may actually have more benefits.

Here's some food for thought:

On a car, we all know, the bigger the discs, the better the brakes are likely to be:


So why would small discs on bicycle be better than the huuuuge 'disc' that the edge of the rim effectively creates?


Well, it's not really that simple, and I think large discs on cars have more to do with surface area, and not just diameter.


That aside, here's a few reasons why I think discs are way better than rim brakes:

1) Discs are better in the wet. They don't get as wet and dirty as the sides of the rim, and they could be considered self-cleaning to a degree. This makes a massive difference, especially on MTBs.

2) When your rim gets a bit bent, your rim brakes will start to misbehave. Discs will continue to function perfectly! Bent rims are inevitable when it comes to bicycling.

3) Easier to set-up and fine-tune. Especially taking into account the point above...

However, it seems that rim-brakes still seem to have advantages over discs when it comes to overall weight & aerodynamic profile.

Pic from a recent Tour de France (2015/16?):

source

[carmayogi]

Originally Posted by Rehaan

However, it seems that rim-brakes still seem to have advantages over discs when it comes to overall weight & aerodynamic profile.

Pic from a recent Tour de France (2015/16?):
Attachment 1648786
source

I'm an avid bicyclist here in New York City, you can see from my list of vehicles that I went from a Swift Zdi in Bombay to a 9-speed Birdy bike here, with disc brakes.

Some points in favour of disc brakes:

• Disc brakes are better in rain, dirt etc as you mentioned correctly.
• Disc brakes have more emergency stopping power, but has to be used on the rear else you go head over front wheel and tumble unceremoniously!
• Mechanically controlled discs are easier to modulate than rim brakes. Furthermore, hydraulic discs are even easier to modulate, so once you're used to it, you can pull some late braking moves.
• Discs are much easier to clean effectively and stay clean for longer. Pads tend to last longer than on rim brakes.
• If you wear your rim down, you need the expensive and time consuming job of replacing a wheel rim whereas with disc brakes, you just change the rotor.
• Disc brakes look cool.
  

However, bike racers use rim brakes!?

• The biggest reason is falling. When you fall, at speed, a rotating sharp disc can be extremely dangerous. Refer: http://www.cyclingnews.com/news/doul...erious-injury/
• Aerodynamics are a factor, although relatively minor. Yet, every 0.01 km/h of speed matters to a mad biker.
• Pro racers tend not to care if their rims wear out as they change them regularly, even during or in between stages of a race.
• Race bikers tend to not use brakes as much as they can. They often plan ahead and can be seen sitting upright to use their body as an "air brake", Bugatti Veyron/Chiron style!! On downhill stretches, you may see some maniacs doing 80+ km/h in this country!

Hope this is useful information!

[Tgo]

Originally Posted by Rehaan

That aside, here's a few reasons why I think discs are way better than rim brakes:

Originally Posted by carmayogi

Some points in favour of disc brakes:

That's all true along with a couple more things I could think of favouring Discs:

• I've also seen that the rim brake shoes wear out unevenly (they become tapered) because of the leading action of the shoe. This requires frequent swapping from left to right to wring the life out of them. This isn't the case with disk pads.
• For mountain bikes running downhill for extended durations, the discs offer better resistance to fade (presumably) due to better heat dissipation.

[manishym]

Excellent points carmayoogi. One more reason for pro bikers not preferring disk brakes is the weight. It may not seem much to us, but for race bikes, every gram of weight that can be shed is a lot of value. That is the reason we see bike frames which are 100gm less than others commanding a 70k premium over others. So adding a 200gm disk to a bike would be a strict no for racing bikes, however any pro mountain biker would be using disk brakes because of superior braking abilities.

[groom]

The disc brakes on such bikes come with a risk of rear wheel lift up. The brake bite is good, but force distribution is bad. As most of these bikes reach a good top speed, the brake performance comes with risk. IMO.

[opendro]

First, thank you for an excellent post on the mechanical disc brakes on bikes, which you aptly call cable-operated. I just wanted to warn you on this point below:

Originally Posted by Tgo

Some points I learned while working on the disc brakes:

• Everything from the Brake Lever to the cam mechanism must be approriately lubricated but the brake pads and disc must not be contaminated with them at all.

Oiling cable housing in bikes was the thing of past or of Indian made bikes. Even with oil, Indian bikes will never work smooth. It is because of the cable housing. Imported bikes have cable housing that has an inner lining of very low friction. The cable should be completely clean and dry. Putting lubricating oil will irreparably jam this low friction lining in no time.

Unfortunately, even a multinational stores like decathlon mentions that we should lubricate : https://www.decathlon.in/p/8043621_b.../3741-99-black

I had spoiled my super smooth brakes of a Merida bike by lubricating. Here is what the best bicycle expert in the world has to say : https://www.sheldonbrown.com/cables.html#lubrication

Trust me on this. Please change the cable housing, clean the cable completely and install again for feather touch operation of the brake lever.

Originally Posted by Tgo

That's all true along with a couple more tings I could think of favouring Discs:

• I've also seen that the rim brake shoes wear out unevenly (they become tapered) because of the leading action of the shoe. This requires frequent swapping from left to right to wring the life out of them. This isn't the case with disk pads.

This is a common phenomenon among many bikers. But it shouldn't have to this way if installed properly. In a typical V brake, which is the post popular one among commuters (hybrid) and even many non-professional MTBs, the brake arms should be slightly outward when pad is new and slightly inward when pad is worn out. Since the action of the brake arm is rotational in nature, it is inevitable that the upper part will wear out. I have not faced this myself. I can check if the pad has more thickness in the top than the bottom and update later. Meanwhile, here is a read on the adjustment : https://www.sheldonbrown.com/rim-brakes.html#shoeadj

We also cannot swap left and right of the pads in most pads I know of - neither in road bike nor in V brakes. They are marked L and R. Even if we want to disrespect the marking, the nut on the pad is not exactly in the middle of the pad and it would affect the nature of the pad's functioning.

[Tgo]

Originally Posted by opendro

Trust me on this. Please change the cable housing, clean the cable completely and install again for feather touch operation of the brake lever.

Great input. Never knew about the low friction lining.

Originally Posted by opendro

Since the action of the brake arm is rotational in nature, it is inevitable that the upper part will wear out. I have not faced this myself

We also cannot swap left and right of the pads in most pads I know of - ...the nut on the pad is not exactly in the middle of the pad and it would affect the nature of the pad's functioning.

Meanwhile, here is a read on the adjustment : https://www.sheldonbrown.com/rim-brakes.html#shoeadj

I was talking of the brakes wearing out in a taper along their length as the left pad in the picture below:


Source: bicycles.stackexchange.com

Swapping left to right is fine I guess if the nut you said is in the middle of the pad? I'm just talking with reference to leisure cycling, nothing close to even semi professional.

Great article on V-brakes. Thanks for pointing me to this site.

[Rehaan]

Originally Posted by carmayogi

The biggest reason is falling. When you fall, at speed, a rotating sharp disc can be extremely dangerous. Refer: http://www.cyclingnews.com/news/doul...erious-injury/

Wow! Had never even considered that....

Originally Posted by carmayogi

Race bikers tend to not use brakes as much as they can. They often plan ahead and can be seen sitting upright to use their body as an "air brake", Bugatti Veyron/Chiron style!!

Mmmm.. not sure i agree with you (or your phrasing) here. To get the best timing on a course, you want the maximum amount of braking (deceleration) in the minimum amount of time. That simply enables you to keep a higher speed for longer, making you faster overall.

Body as an "air brake" might be used strategically, or in combination with the actual brakes (ala Veyron).

Originally Posted by groom

The disc brakes on such bikes come with a risk of rear wheel lift up. The brake bite is good, but force distribution is bad.

With more braking power it's certainly easy to go flying over your handlebars, but the fact is that discs are more sensitive, and a good disc system lets you modulate the brakes a lot more accurately.

Your body needs to re-tune to the new brakes, but there's no additional risk involved once that's done.


As an aside, I had these on my bike. Avid Speeddial levers.

They are cool because you can actually adjust the sensitivity (ie. leverage) of the lever. Rotating the knob changes the distance of the cable endpoint from the fulcrum - which changes the amount of effort / sensitivity of the brakes. Pretty awesome:


source

[carmayogi]

Originally Posted by groom

The disc brakes on such bikes come with a risk of rear wheel lift up. The brake bite is good, but force distribution is bad. As most of these bikes reach a good top speed, the brake performance comes with risk. IMO.

Originally Posted by Rehaan

Mmmm.. not sure i agree with you (or your phrasing) here. To get the best timing on a course, you want the maximum amount of braking (deceleration) in the minimum amount of time. That simply enables you to keep a higher speed for longer, making you faster overall.

With more braking power it's certainly easy to go flying over your handlebars, but the fact is that discs are more sensitive, and a good disc system lets you modulate the brakes a lot more accurately. Your body needs to re-tune to the new brakes, but there's no additional risk involved once that's done.

As an aside, I had these on my bike. Avid Speeddial levers.

Few points to clarify.

Going head over heels happens when you brake the front wheel too much. On a bike weight distribution is supposed to be rear biased which is why rear tires wear out quicker. The ideal braking technique is to first, sit up straight from crouched forward position, thus putting weight back. The upright position adds air resistance. Guess my wording was wrong. Then use rear brakes for heavier braking with lighter braking in the front, using your core muscles to hold the body upright and not lean forward. Even motorbike racers use the same technique of sit-up-straight braking although they have a lot more grip, braking power, mass, etc. As @Rehaan said - once you get a feel for it, it's quite difficult to go head-over-heels. I have done it once, while in the process of getting hit by a car!!

As far as modulation is concerned, there are hydraulic & mechanical discs. Mechanical are difficult to modulate and become worse when the pads/disc is dirty because they grab quite suddenly. Regular cleaning with alcohol on the metal disc is always recommended. Hydraulic brakes, much like in a car, have a lovely squishy brake level feel, you can really squeeze in incremental amounts without locking up.

@Rehaan those AVID levers look interesting. However, most brakes have adjustments on the cable to change the 'bite' point. This seems to have a lever adjustment that changes the feel of the lever to suit your needs.

All of this is reminding me to clean my brakes. New York City streets give Mumbai streets some serious competition for potholes, dirt, puddles, muck and miscellaneous s**t!

[carmayogi]

Originally Posted by opendro

Here is what the best bicycle expert in the world has to say : https://www.sheldonbrown.com/cables.html#lubrication

Sheldon Brown is 100% the best resource for useful, well-researched information on bikes, maintenance, components - you name it. The website design is unfortunate, but get beyond that and you find all sorts of pearls of wisdom.

[groom]

Here is some interesting information coming on the ABS for e-bikes, slightly off topic but related to very much what is discussed in this thread.

https://www.bosch-ebike.com/en/news-...new-ebike-abs/