Kona ute miniute Avid B55 byicle mechanical disc brake system

Some cyclists feel unsafe with mechanical bicycle brakes bit spongy a trend towards hydraulic brake bikes. Most of us never do like slack pulling up efficiency on any bike anyway. The cause is often DIY ( do it yourself ) fixing producers.

Kona chose a mechanical disc brake brand Avid BB5 for their Kona ute and miniute cargo bike brake range. Mechanical disc brake systems are basically the same arrangement as any garden variety rim brake bikes.

In dealing with the Kona ute and mini ute braking system we will be concentrating on the Avid B55 mechanical brake system. When you squeeze the handle bar lever only one pad is pressed against the Rotor ( Disc ). The opposite pad other side is fixed. If you're used to rim brakes it is a mistake to forget only one pad moves in this system.

Looking down between the crack of the caliper on the wheel the rotor runs between as you squeeze the handle bar lever you will observe the moving pad pushes the rotor bending it over onto the fixed pad. The gap of the fixed pad limits the rotor bending. If the gap is to wide there will be a severe bend of the rotator ending up with a slack braking power when you squeeze the handle bar.

If the you ride in all sessions it is inevitable winter conditions corrodes the moving parts of the brake system offering a fair amount resistance to the spring to pull back the moving pad from the rotor.

Often another cause of slack braking is DIY reassembling of inner wire cables that can be a source of endless frustration. If inner cable is at an angle can cause slack spring force to open the pads compounded by corroding brake arm to pull away from the rotor. Both pads half dragging on it wearing a trench round the circumference. Comparing new bikes at bike shops is a clear indication of what conditions of rotors should be.

Examining the inner wire cable anchored on the brake arm of both rim and mechanical brake bikes at any bike shop the inner wire cables are always straight looking. They are not slopping at any angle a clear initiation of what the inner wire cable should be anchored like. If the cable of you bike is on an angle it needs to be undone and remounted straight.

To begin the bike can either be left up right on it's wheels or turned upside down resting on the seat and handle bars it's up to you. Professional workshops have bike stands everything chest height both wheels off the the floor. In a backyard situation with the bike upside down the wheels are free to rotate when adjusting the pads to the the rotor.

There are various fasteners round all bikes....... gear changers......brakes........commonly hex ( six sided ) Allan key bolts. Never forget nuts and bolts come in metric and imperil including hex Allan key spanners. Check the cable fastener selecting a key that fits properly noting the size for reference benefits.

One of the most frustrating things are well weathered bolts that can be pretty rusty looking. It's safe bet are seized on by corrosion that can be the most frustrating to shift we tend to force applying weight often to much for standard Allan keys rounding the corners of both the bolt and key beyond use. The worse thing is having no resources to shift them with.

In such a case a two dolor shop could be able to supply a fairly inexpensive way of building a seized on bolt removing tool. Interchangeable screw driver piece set where individual bits that fit into a screw driver shanks are very helpful. You will need a star bit even a common Phillips star type can do the job that is a very tight fit in the hex bolt. Tap gently into the hex head.

The screw drivers never will be able to shift a seized on bolt on their own. Shifting spanner ( or crescent, even vice grips ) as a wrench will be ideal. Small cheep and well warn crescents are not recommended as the worn out movement gives the minimum amount of stable grip slipping and sliding off when you apply weight rounding the edges of the bit as well as making a mess of everything else. Medium to hefty new to near new condition spanners give maximum stable grips. For those with resources adaptors for the bit for use for socket sets you can make up a socket set wrench with. With a stable grip you should be able to shift loose a seized bolt coming free with a crack. You should be able to tap free a vice grip clapped on the shank of the piece.  

The Avid B55 break system has a ledge on the cable anchor arm used as the cable guide. In this system the inner cable resting over the top is incorrect what causes the angling of the inner cable and adding a bend in it. If done to any B55 brake caliper you will find problems with a hopelessly distorted and chewed up frayed cable. If lucky you may get away with no frays and minimum distortion. If a cable is badly distorted chewed up crushed and fayed with many broken individual wires it will be impossible to used safely ever again. Either way either replacing of relocating the inner wire undo the bolt and pull away the entire cable.

The Kona ute and mini ute handle bar ends are basically the same as any standard mechanical rim brake bikes. If your used to rim brake bikes the replacement of the ute and miniute is pretty much straight forward. Once the cable in place you can hook up, to the caliper brake arm.

If the handle bar adjusters are adjusted at maximum ( or close to it ) causes a fair bit of bending stress on the threads when squeezing the brake levers helping strip the adjuster threads. Squeezing takes it's tool. So too to a lesser extent the adjuster on the caliper.  To prevent and solve this problem screw the adjusters all the way back to nil.

If your used to rim brakes remember not to forget in this case both pads don't move like them. The adjustment of the fixed pad sets the setting the moving pad.

Turn you attention on the spoke side of the caliper. In the center is Allen key bolt. This adjustment adjusts the fixed pad. An Allan key through the spokes turning inward adjusts the fixed pad towards the rotor and screwing outwards away from it. Screw inwards finger tight on the rotor turning the wheel to check that it jams the wheel. Looking down the gap the disc runs between adjust the pad a millimeter gap away from the rotor. When you come to assemble the cable to the moving arm the cable is anchored the pad equally a millimeter away from the rotor  

Avoid laying the inner cable on the top of the ridge. Let the cable rest along the edge.

Depending on whether your left or right handed with one hand push the brake arm moving the brake pad to the rotor and with the other hand pull the tail of the cable to take up the slack. The distance of the pad from the rotor can be judged pretty closely by eye eyeing down between the crack of the caliper the disc runs between. You will feel a bit of a struggle against the spring  tension witch inevitably makes things difficult. Keep a firm tension on the brake arm.

Allowing the cable to rest along the edge of the ridge align the double lugs of the clamper with the edge. As you tighten the bolt friction drags the clamper a full quarter circle the lugs pulling the inner wire round in a right angle ( an L bend ). Avoid any thoughts of maximum tightness. All you need is a light almost finger tight tug to finish off. The inner cable will be straight. You will now get more efficient braking.

Test the wheel spinning it gripping the handle bar levers so the wheel jambs instantly to a stop. Remember to bear in mind all bike manufactures can't afford to allow severer brakes specially the front wheel in fear of back lash law suites riders going over the handle bars because the form wheel because their models front wheel have a habit of locking up. It is the reason for criticism the B55 not very efficient. As you hold the lever the wheel should be jammed in position.

Replacing pads

The disassembly and reassembly of the brake cable is already been covered.  Accessing the pads small parts when the wheel of off out of the away can easily fall out and get lost falling to the ground spending all your time looking for them that could fall anywhere. It pays to put a catcher tray in direct line the parts may fall caching them so you don't loose them.

In some cases you may not need to remove the inner cable from the caliper anchor bolt which is handy. In other cases disconnecting the wire cable is standard practice.

What ever the case may be concentrate adjusting the fixed pad adjuster bolt outward it will go. You will find when you remove the wheel the pads won't interfere catching the rotor. The wheel will come off just like that. The same Allen key that fits the fixed pad cable adjuster will fit the two bolts on the wheel side of the caliper. Don't be shy to put some weight on them to undo. If they appear to be sized on from the whether freeing them has been covered. Don't be rough unscrewing because of the aluminum threads. They must be with drawn out dead straight.

Once the bolts are withdrawn the cover comes off, along with the spring may fall into your catcher. Remember you are handling the brake pads from now on so your hands should be pristine clean to insure you don't transfer oil and crease to the oil absorbing pads and rotor.

Examining the spring is a “V” shaped steel spring as seem in the left picture each tip crumpled each end a "u" shape hook that fits in a slot in each pad. The spring is effectively sandwiched between them.

Notice the hole in the center of the pad. This refits to the corresponding peg in the covers. Make sure you reassemble the pad hole in the corresponding pegs in the caliper covers properly.

Reassembly is tricky as it is a bit fiddly. Fit a pad color side into the corresponding recesses in the caliper cover fitting the spring in the corresponding pad slot as shown by the left picture. Make sure the center hole is fitted in the peg properly

Correspondingly fit the other pad color inwards the cover recess guiding it hooking the tip of the spring into the hook in the slot of that pad.

Line up the cover to the threads. Careless fitting of the two bolts into theses threads here is the major cause of stripping the caliper threads rendering the bolts useless. Screw the bolts carefully dead straight with only fingers. Never force them with the spanner if they feel a bit tight. Carefully withdraw and jiggle the cover a bit so the bolts can finger screw with out any grinding tight feel freedom of movement.

The final tighten of the bolts is another area will strip the caliper threads. Don't wrench thinking maximum tightness. A light tug they can't tighten any and no more. If the inner wire cable was disconnected is the final stage adjusting the moving pad  already covered