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BrakesAndCables

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Brakes and Cables covers theory of cables and their maintenance, as well as adjustment and maintenance of brakes and pads.

Outline:


  • [T] Cable theory
  • [T] Advanced cable theory
  • [A] Lubing cables
  • [T] Barrel adjusters
  • [A] Repair stand use
  • [T] Types of brakes
  • [T] Brake adjust theory
  • [T] Adjusting brakes - cable tension
  • [T] Adjusting brakes - pad position
  • [T] Adjusting brakes - centering
  • [T] Brake adjust theory
  • [A] Adjusting Brakes
  • [A] Brake pad care

11/08 notes for new 2-part class (disregard this for now...)

Brakes and Cables(all M except as noted)
(R) Repair stand use (as needed)
Cable theory
(R) Advanced cable theory
Lubing cables
Barrel adjusters
(R) Types of brakes
Brake adjust theory
Adjusting brakes - cable tension
Adjusting brakes - pad position
Adjusting brakes - centering
Brake adjust theory
Adjusting Brakes
Brake pad care
(R) cable installing
(R) compatibility

CONTENTS OF DEMO PARTS BOX
Cable friction demo: black (shift) is smooth, silver (brake) is kinked, corroded, and old (no sleeve) housing, and old (not smoothed) cable.
Gor-tex coated cable ($40/set, CAN"T be lubed)
3 Cable heads
ends: new (welded) vs. cut (frayed)
un-raveled strand
Breaking at head
overtightened draw bolt (on saddle) anchor, and draw bolt without cable
New pinch-type cable anchor
shift housing with splayed end, split housing
Vbrake adjust, canti adhust
pads: new (wear slots), fully used, down to metal, mis-adjusted, contaminated with rim material... others?
3rd hand, 4th hand, cutters, centering tools

JOHN — add to this above if you think I missed something in the box; done from memory.

Cable Theory

Cables exist to transmit force and position from one part of the bicycle to another. This is so obvious that it's easy to lose sight of it and think of cables as abstract things. They aren't, they're brutally simple devices. Keeping it in mind makes cables much easier to understand. The other key concept is housing. Cables are always under tension, so they can only go around corners if they're touching something. Housing provides a surface for them to touch as they turn corners. These two facts make the need for lubing cables obvious. Cables can't transmit force as well if it's being wasted on friction, and they can't transmit position accurately if they're hung up on something. Since they're in constant contact with housing, it can create a lot of friction if it isn't properly lubricated. Before moving on to lubrication, show the demo parts for different cable ends and different housing types.

PART

Advanced Cable Theory

It is usually worthwhile to explain the reasons for using a different housing for indexed shifting than for friction shifting and braking, and things such as machined cables and coatings. Everyone, however, should understand that the wires in shift housing run lengthwise, and that it absolutely requires housing caps to keep it from fraying. Also mention cable tip crimps.


Lubing Cables

Having just explained the reason for lubing, be sure to mention the reason for lubing before adjusting: that it is impossible to adjust something (brakes or derailleurs) well if it is not well lubed. Show students how to get housing out of split stops (shifting into the biggest cog in rear, then moving the shifter to the lowest tension position without pedalling, just shifting to the small cog in the front, quick releasing brakes or loosening barrel adjusters). Show the lubing process for split stops, and the lubing process for non-split stops. Students lube their own brake cables. It is a good idea to be nearby to hold the bike up for people with non-split stops, since it puts the stand in a rather unstable position.

Barrel Adjusters

You might have needed to turn someone's barrel adjuster to get slack, and if so that might be a good time to explain them. Barrel adjusters are very difficult to understand. This is probably due mostly to two reasons: they make things tighter when you "loosen" them, and they are often at such odd angles that it is difficult to tell which way is tighter. There are a few methods for teaching them that work decently. One is to repeat several times that one needs to unscrew the barrel adjuster to make the cable tighter. The other, which works better on brakes, is to suggest trying to turn the adjuster both ways a bit, and whichever way is harder is probably tightening the cable. Whatever you can do to get the point across, be sure you do it, because barrel adjusters are a key concept in that their use is a maintenance item which is really intended to be performed by the rider.


Repair stand use

If the Wheels and Bearings class the previous week was taught without stands, show the repair stands and explain how the clamps work. Explain why it's usually best to clamp around the seatpost, and point out the white stand with exposed metal on the clamp, which makes it even more important. The top tube also works well if it doesn't interfere with the rear brake cable. Mention marking seatpost height with a pen if raising the seat to get enough post to fit in the clamp, as opposed to scoring and creating a stress concentration.

Types of Brakes

Explain the two fundamental types of brakes, rim brakes and hub brakes. Then break hub brakes down into disc and internal, and explain the difference between them briefly and get them out of the way because the course doesn't cover them. Hub brakes in general perform very well in wet conditions, and internal hub brakes in particular usually require very little service. Disc brakes can get warped rotors (and can be dangerous to work on — one member recently cut off a finger end), and need a special frame and hubs. Coaster brakes don't have cables to maintain, but don't work properly if you lose the bolt holding the arm to the frame, or burn up the grease inside, which can happen on long downhills. They are not very strong if you don't also have a front brake, and in that case you'll also have NO brakes if lose your chain or a pedal.

Moving on to rim brakes, explain the two different ways that rim brakes attach to the frame, and that caliper brakes, which attach via one bolt above the wheel, are commonly called road brakes, and that cantilever brakes, which attach to two posts beside the rim, are commonly called mountain brakes. This is best done with an example. From there, describe the four basic types of rim brakes, also best done with examples:
  • Sidepull calipers: The standard brake for road racing bikes, mounted above the wheel with one bolt and actuated by a cable which runs with housing all the way to the brake arm. No serious problems, but it is difficult for them to be strong and fit around large tires. They are essentially the lightest brakes.
  • Centerpull calipers: Common brakes on cheaper road bikes up until the 1970s, mounted above the wheel with one bolt and actuated by a cable whose housing stops above the brake and pulls on a cable that runs between the two sides. Almost completely unseen on new bikes, common at the co-op.
  • Centerpull cantilevers: Actuated almost the same way as centerpull calipers, but comprised of two arms that mount to posts which are beside the wheel. Adjusting the pads is terribly difficult on old models because they can move in too many directions. Almost completely unseen on new bikes other than touring and cyclocross bikes, but relatively common on mountain bikes at the co-op. Stop very well, and can fit around big tires.
  • Linear pull cantilevers: Actuated like sidepull calipers, with the housing running all the way to the brake arm, although the last piece of housing is a stiff "noodle" which is considered to be part of the brake (show one). They require more cable travel, so they need different levers than the other three types. Common on new mountain bikes, comfort bikes, and some touring and cyclocross bikes. Easy to adjust, easy to release and very powerful with good modulation. Mention that their common name is "V brakes", because that's what Shimano calls them.

Brake adjust theory

Before getting into the process of actually doing it, go over the goals of adjusting brakes. The pads should be close enough to the rims that squeezing the levers can generate maximum stopping force; the simple test for this is to see if the rider can get the brake levers to touch the bars. The pads should not be too close - spinning the wheel should not make them touch the rim in places where the wheel is out of true. The pad surfaces should contact the rim fully, without going over or under. The pads should be toed in a bit to avoid squeaking. The brakes should be centered.

Adjusting Brakes - cable tension

All brakes should have a barrel adjuster, either on the lever on bikes with flat bars or on the brake on bikes with road brakes. Bikes with flat bars and road brakes may have two. If they don't provide enough, cable tension can be adjusted by loosening the pinch bolt. Explain this and the use of the third hand.

Adjusting Brakes - pad position

The process is fairly similar and straightforward for caliper brakes and linear pull brakes. Emphasize making sure the entire pad surface contacts the rim, and on brakes (mostly linear pull) with washers that permit a change in pad angle, demonstrate the ability to adjust toe-in as well. Also show and explain the toe-in tool and its use. For cantilevers, explain why they are hard and be prepared to step in and get them right.

Adjusting Brakes - centering

The brakes need to be centered so that they contact the rim at approximately the same time and so that they can be adjusted to be close enough to the rim for maximum stopping power. On sidepull cantilevers, show the method of hitting the spring with a drift of some sort. For cantilevers of both kinds, show the use of the adjusting screws.

Adjusting Brakes

Students adjust their brakes with instructor help. This is a fairly difficult process, and the idea is mostly to make people aware of what incorrectly adjusted brakes are like - levers hitting the bar, pads hitting the tire or going under the rim. Be prepared to be hands on here.

Brake Pad Care

Show the demo part of a brake pad with chunks of aluminum in it and explain what this can do to rims, and how to clean it. Students clean their brake pads. Anyone with road brakes will need to take their wheels off for this. Some mountain brakes will manage without. If time is running short, the actual cleaning can be skipped if you let them know how to do it and maybe take a quick look at their pads.


Created by: pgarver. Last Modification: Tuesday 05 of May, 2009 22:45:54 UTC by JSheehan.