Norton Commando Workshop Manual

## Brakes, Weels and Tyres

# H

7 | Take the master cylinder assembly in the left hand (having assembled up to the point as described above) supporting the casting with the first and second fingers under the switch boss (hose and pressure switch threaded bores pointing downwards) and left thumb on the top of the casting close to the piston thrust "pad." Apply a gentle rotary action with the right hand to the piston thrust pad, at the same time maintaining downward thrust pressure against the trap valve spring assembly - ensuring the lip of the secondary cup enters the cylinder bore freely and without damage to the lip. When the piston has entered the bore, move the left thumb over to maintain the piston within the bore, at the same time using a blunt prod to snug the lower boot shoulder into the cylinder counter bore. Once this is seen to be achieved, and still maintaining pressure on the piston thrust pad, work the boot retaining circlip down to locate and restrain the boot in position. Still maintaining pressure on the piston thrust pad with the left humb, slide the brake lever into position at the fulcrum slot, engaging the thrust pad close to the operator's left thumb. By holding the lever knob against the chest, alignment of the holes can be achieved, and the pivot bolt slid into position, and located with the locknut.
Master Cylinder Refitting
Refitting the master cylinder is the exact reverse procedure of the dismantling sequence described above. Refit the master cylinder to the handlebar, the oil pressure switch and brake hose. Slide the plastic switch cover over the hose, hold in a convenient location whilst the brake light wires are connected to the brake switch terminals and slide the cover into final location. Enter the lower hose into the fork support bracket, locate in position with the locknut and tighten up the upper brake pipe union nut. Bleed the hydraulic system as described in the following text, after ensuring that the master cylinder is level on the handlebar.
Bleeding the Hydraulic Brake System
1 | Remove the reservoir cap and fill the reservoir almost to the top. Remember that brake fluid ruins paintwork and do not allow fluid to spill during filling.
2 | Connect a small bore rubber tube from the caliper bleed screw to a clean jar or receptacle.

3 | Unscrew the bleed screw one full turn and start to pump slowly the handlebar lever. As fluid is forced to the caliper and through the bleed nipple, the master cylinder level will drop. Take care throughout the operation that the level does not drop sufficiently low to allow further air to be pumped into the system and top up where necessary.
4 | Continue pumping the lever until fluid free of air bubbles exits from the bleed tube into the fluid container then hold the brake lever "on" against the handlebar whilst the caliper bleed screw is tightened and the bleed tube removed.
5 | Test the brake for "sponginess." If the action feels "spongy," then air remains in the system and further bleeding must be undertaken.
6 | Ensure that the master cylinder reservoir is brought to the correct level then refit the bellows seal and cap.
7 | Finally check all unions for security and freedom from leaks.

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