Bicycle Technology: Hub Brakes

Although not used very much on quality bicycles these days, the alternative way of stopping a moving vehicle by means of brakes contained in the wheel hubs remains of considerable technical interest. Used on virtually all other vehicles in some form or another, hub brakes can’t be all wrong. Besides the coaster brake, which is operated by pedaling backward, there are several other brakes that are built into the wheel. All these will be covered in the present section: drum brake, disk brake, roller brake, band brake and expansion- contraction brake. Except for the former two, which are popular mainly in Europe, the others are primarily known as Japanese products.

The advantage of any hub brake is its insensitivity to rain, sleet and snow: being tucked away nicely inside, these banes to the conventional rim brake don’t have a negative effect on their performance. Their disadvantage is mainly in the mind: it’s not considered cool to have anything except what is in fashion, and clearly rim brakes are in. Technically, they all have minor problems, but they remain interesting alternatives, as was recently demonstrated in a decent from one of Europe’s steepest and longest mountain roads, where Sachs-Huret’s drum brakes performed superbly.

The common technical disadvantage of all these brakes is that the braking force is applied far from the most effective point (the circumference of the wheel), so it has to overcome the leverage of the distance between the hub and the outside. Furthermore, the braking force must be transmitted via the spokes, while the counter effect is taken up via a restraint that works on an inherently weak point of the bike — the fork blades or the rear stays. All these problems can be solved through the correct selection of dimensions and components. And let’s not forget: all other components on the bike also have some problems.

13.2. Fichtel and Sachs coaster brake with built-in automatic two-speed gearing mechanism.

13.1. Sturmey-Archer Elite aluminum drum brake for the front wheel. Matching units are available for the rear.

Except for the coaster brake and the roller brake, all these brakes are operated just like rim brakes by means of cables, although pull rod systems are available for some drum brakes. The simplicity of pedaling back to stop with the coaster brake and the roller brake may be very appealing, in reality these are a real nuisance, since they make it impossible for the rider to pedal backward to place the pedals in the right position to start off. In practice, this is a more serious problem than the often stated fact that the cranks have to be rotated into the correct position before you can brake.

Generalizing, it can be said that the bigger the brake, the more satisfactory it will be. Bigger brakes have large cooling surfaces. On the rim brake, it is the wheel rim that acts as cooling surface, while it is the outside of the hub on most hub brakes. Checking the size of some coaster brakes and particularly the roller brake, one appreciates that these things, designed for rear wheel use, cannot be suitable for longer descents. So they should always be used in combination with another brake on the front wheel.

The Coaster Brake

Fig. 13.4 illustrates the principle of the world’s most popular coaster brake. Although some models work differently, none are as simple, powerful and reliable as Fichtel and Sachs’ Torpedo brake, which is shown in an exploded view in Fig 13.3 in its simplest form — other models have built-in 3- or 5-speed gear mechanisms. Modern versions of the Bendix brakes, the traditional US make, work on the same principle.

The Torpedo brake incorporates an interesting friction- less freewheel mechanism illustrated in Fig. 13.6. When you stop pedaling forward, the rollers of the free- wheel drop down into the lower position, disengaging the interior from the forward rotating hub shell. When pedaling back, this position of the freewheel rollers allows continued wheel rotation, but at the same time the backward rotation forces the brake cone up a helical groove towards the right, pushing out the segmented brake mantle against the inner braking surface of the hub shell. The resulting friction absorbs the energy and decelerates the wheel. The resulting forces are countered by means of a brake counter-lever that connects the fixed center with the LH chain stay.

13.3 Exploded view of a typical coaster brake. This is Fichtel and Sachs’ Torpedo model.

13.4. Coaster brake operating principle

Coaster Brake Maintenance

The major maintenance described here will be adjustment of the wheel bearings and other bearing work. Coaster brakes tend to run hot when used vigorously over longer distances. In extreme cases, the lubricant burns out of the bearings. If this happens, it is usually sufficient to partly disassemble the bearings arid repack them, using the manufacturer’s recommended special heat-resistant grease.

13.5. This clutch on the Fichtel and Sachs coaster brakes with gearing assures that the brake remains functional even with the gears out of adjustment.

Adjusting Hub Bearings

From time to time, check the bearings as described for the regular hub. If they are too loose or tight, adjust them without removing the wheel from the bike. Use the special wrench supplied with the bike or the brake hub (or order it through a bike shop). Refer to Fig. 13.7.

Procedure:

1. Loosen the LH axle nut 2 - 3 turns.

2. Loosen the round locknut with recesses about one turn.

3. If the hub is equipped with a square end on the RH axle end, turn it clockwise to loosen the axle, counterclockwise to tighten it.

4. On models without a square axle end, such as those with built-in gearing, remove the locknut al together and loosen the underlying shaped plate that engages the cone: to the left to loosen, the right to tighten the bearing.

5. Tighten first the locknut, countering at the axle or the shaped plate, then the axle nut.

13.6. Frictionless freewheel on Fichtel and Sachs coaster brake. Driving; Freewheeling

The Drum Brake

This type of brake is available for both the front wheel and the rear wheel, the latter in versions with built-in hub gearing or with screw thread for the installation of a regular freewheel block with multiple sprockets for derailleur gearing.

Fig. 13.10 shows how this thing works, while an exploded view of a typical one is depicted in Fig. 13.12. When the brake lever is applied, the attached cam pushes the brake segments apart against the interior of the drum on the hub shell. The resulting friction absorbs the energy, slowing the bike, while the counter- lever fixes the interior against the fork or rear stays. This counter-lever must be quite substantial, as disastrous experiences with early models have proven: they tended to crumple up, as did some of the frames that were not designed for the high local forces.

The material of the brake segment linings should not come in contact with lubricants, since that reduces friction dramatically. This is often a problem on Sturmey-Archer’s models with built in hub gearing, since they lack a seal between the two parts. If this happens, get the brake segments relined (or exchanged) by an automotive brake specialist.

13.7. Loosening or tightening the lockring on a coaster brake bearing.

13.8. Torpedo coaster brake by Fichtel and Sachs.

Fading

The drum brake, whether used on bikes, cars or motor cycles, is quite sensitive to a phenomenon called fading. During long descents, the brake heats up and causes the drum to expand away from the brake liner. As the diameter increases, the surfaces of the two don’t match anymore, leading to a drastically reduced braking effect. The problem is minimized by intermittent front and rear wheel braking, allowing the other one to cool off after every half minute of application.

A related problem that applies to all commercially available drum brakes is the fact that the liners wear asymmetrically, due to the one-sided pivoted arrangement. Since one of the segments spreads in the direction of rotation, the other one in the opposite direction, unfavorable wear results, and the brakes not only be come less effective during long descents, but gradually become less effective over their lifespan as well.

13.9. Adjust bearing play

Drum Brake Maintenance

The brake’s effectiveness is verified as was described for the rim brake in Section 12. Other maintenance operations include adjustment of the cable (or in a control rod on models so operated) and bearing adjustment and maintenance, as well as exchanging the segments when the liners are worn or contaminated. In the latter case, disassemble and remove the old segments which can be exchanged by a brake specialist.

Adjusting Drum Brake

Essentially, this is done as on any other hand-operated brake. The cable adjuster is used to increase the cable tension if the brake does not engage properly, and is loosened if it does not clear when the lever is released. As with the rim brake, the cable, the lever, the guides and the anchors must be checked first, since these points are the most frequent causes of improper operation. If necessary they must be cleaned, freed, lubricated or replaced when adjustment does not have the desired effect.

13.10 and 13.11. Left: Operating principle of drum brake. Right: Sachs-Huret drum brake for mountain bike use. On bikes with front suspension, this is a good brake to use.

13.12: Exploded view of typical drum brake (Sturmey-Archer ill.).

13.13. Sturmey-Archer rear wheel drum brake for use with derailleur gearing (a standard six-speed freewheel block can be installed).

Adjusting Hub Bearings

The need for this is established as described in Section 8 for the regular hub. All you need is a wrench and the special hub wrench that may be available for the particular model. Fig. 13.14 shows the parts that are affected, while the wheel may be left on the bike.

Procedure:

1. Loosen the axle nut on the control side by 3 - 4 turns.

2. Loosen the locknut by 1 - 2 turns, and lift the lock washer.

3. The adjusting plate, which engages the bearing cone, can now be turned to the right to tighten the bearings, or to the left to loosen them.

4. Hold the adjusting plate while tightening the lock nut.

5. Tighten the axle nut, making sure the wheel is properly centered.

6. Check and repeat the adjustment if necessary.

13.14. Bearing adjustment detail

13.4a. Coupled pull-rod operation of both drum brakes from either brake lever, as used on a Dutch utility bike.

Overhauling Drum Brake

This can become necessary when the bearings or brake liners are so far worn or damaged that adjusting does not solve the problem. The wheel must be removed from the bike, also disengaging the control cable and removing the bolt that holds the counter-lever to the fork or the chain stay. Refer to Fig. 13.12 for the way the hub is assembled.

Disassembly procedure:

1. Loosen the locknut completely and remove the lock washer.

2. Loosen the cone by means of the adjusting plate (or, after removing the latter, by means of a wrench), and remove it.

3. Remove the mounting plate on which the entire mechanism is installed, while catching the bearing balls, which are usually contained in a retainer.

Maintenance and reassembly:

1. Clean and inspect all components:

- Replace the brake segments if they are worn down to less than 3mm (1/8”) in any location or when they are contaminated with oil and simply roughing them with steel wire wool does not restore them;

- Replace the ball bearings with their retainer and any other bearing components that are damaged (pitted, grooved, corroded);

2. Fill the bearing cups with bearing grease and push the bearing balls into the cups.

3. Apply just a little grease to the pivot and the cam on which the brake segments sit.

4. Wipe excess grease away to make sure it cannot reach the brake liners or brake mantle.

5. Install the mounting plate with the installed brake segments.

6. Screw the cone in and tighten it with the aid of the adjusting plate.

7. Install the lock washer and the locknut, while holding the adjusting plate so it does not turn.

8. Check the bearing and adjust as necessary.

9. Once the wheel is installed, check brake operation and adjust the cable tension if necessary.

Other Hub Brakes

13.15 and 13.16. Left: Operating principle of disk brake (basically, it works like a caliper rim brake, except that the braking surface is flat and rigid and closer to the center of the wheel). Right: Overall view of a typical disk broke.

All other types of hub brakes will be covered only for interest’s sake. Due to their variety, no detailed maintenance instructions can be given here. Even so, with a little imagination and experience, gained on other bike maintenance operations, it will generally be possible to figure out what to do and how to go about it.

Separate Drum Brake

This is a variant of the drum brake that is not an integral part of the hub but is screwed on the threaded end of a special hub by the same maker — usually Araya. It is intended only for use on the rear wheel, arid its most common application is on tandems. Everything said about the conventional drum brake applies here too.

The Disk Brake

Fig. 13.15 shows the principle of the disk brake, while Fig. 13.16 illustrates a typical model made for bicycle use. These too are generally of oriental origin, although some American manufacturers, such as Phil Wood, also offer them. Basically, the rim brake works on the same principle, except that on the real disk brake the disk is smaller and more solid. Since the disk and the brake pads are designed to run hot, this brake can be quite effective, although it does have a tendency to grab, unless used very gingerly. If you clean the disk occasionally, it will work a long time before the pads have to be replaced. Pad wear is checked by means of reference mark visible from a viewing port. Any brake specialist can replace the pads when they are worn.

The Band Brake

Seen mainly in the Far East, this is essentially a drum brake turned inside-out. As shown in Fig 13.17, a strap is pulled inward against the exterior of a brake drum, causing friction. Although it is a remarkably powerful brake, it suffers from overheating on longer descents because the surface that heats up is not directly exposed to the cooling air. This feature makes it inferior to the contracting drum brakes and most other rim and hub brakes.

13.17 and 13.18. Two unconventional hub brakes. Left: Operating principle of simple band brake. Right: Operating principle of contraction-expansion brake (essentially a drum brake and a band brake in one).

The Contraction-Expansion Brake

This rare bird is sold by Bridgestone under the designation Dynex. As illustrated in Fig. 13.18, it combines the principles of the drum brake and the band brake, simultaneously pushing and pulling brake shoes against both the inside and the outside of a heavy brake drum directly connected to a mounting plate with cooling fins. It works very well, due largely to the fact that the effect of fading in the one mode is compensated by Increased braking force in the other.

13.19 and 13.20. Left: Bridgestone Dynex contraction- expansion brake. Right: Band brake on Japanese utility bicycle.

The Roller Brake

A little rear brake that is found primarily on Formula-1 kid’s bikes. Its operating principle is shown in Fig. 13.21 and corresponds to that of the unique freewheel used in Fichtel and Sachs’ coaster brakes. When pedaling back, the rollers travel up the inclined recesses and contact the brake mantle. It works very well for short- time braking but is unsafe for longer descents due to overheating on account of the brake’s miniscule cooling surface.

13.21. Operating principle of roller brake: Driving / freewheeling vs. Braking