7. Front brake master cylinder: removal, examination and refitting
To dismantle the system. attach clear tubing to the bleed nipple of each of the brake calipers, open the nipples by one
full turn, and apply the front brake lever repeatedly to expel all the fluid. When no more fluid can be seen issuing from the nipples, tighten
down each one. Slacken and remove the single screw which retains the twistgrip top cover, then remove the cover and disconnect the throttle cable.
Unscrew the single clamping screw and withdraw carefully the right-hand switch cluster from the rear of the twistgrip assembly.
Note that the master cylinder and fluid reservoir can be detached from the main handlebar unit by removing the two small Allen
screws, or the entire unit can be removed from the handlebars by disconnecting the stop lamp front switch wire and the brake hose, by removing
the handlebar end weight (where fitted) and slackening the single clamp screw.
Disconnect the brake hose either at the master cylinder end or (after removing the handlebar panel) at the union above the
steering head. In either case place clean rags or similar around the area of the union to prevent brake fluid splashing on to any other components,
particularly those that are painted or made of plastic.
With the master cylinder assembly disconnected and removed from the handlebar unit, remove the retaining screws and withdraw
the reservoir cap with its gasket (fitted on early 100 models only) and diaphragm. If necessary, the reservoir body can be separated from the master
cylinder by removing the single retaining screw and pulling off the reservoir with a twisting motion as if unscrewing it. The sealing 0-ring fitted
to the reservoir joint must be renewed whenever it is disturbed, regardless of its apparent condition.
Using a suitable sharp-pointed instrument, prise out the circlip from the master cylinder right-hand end, then pull out the
piston assembly and return spring. Examine all the components closely, renewing any that are found to be worn or in any way damaged. Remember that
it is essential that the master cylinder is maintained at peak efficiency if the brakes are to be in a safe and usable condition.
When purchasing new components note that the reservoir cover has been modified twice on early 100 models to improve its sealing
properties; the second modification included the omission of the cover gasket, which applies to all 75 models. The piston assembly was also
modified on early 100 models; only use the modified type of piston (identified by its dark grey coating as opposed to the earlier golden yellow finish)
which is fitted as standard to all 75 models.
Carefully clean and lubricate all components prior to reassembly, using only clean hydraulic fluid. Reassembly is the reverse
of the dismantling procedure described above, remembering that the use of new seals is recommended at all applicable joints and brake hose unions.
Refill the system and remove all traces of air bubbles by bleeding as described in Section 9, then wash off any surplus brake fluid using copious
quantities of fresh water and check for any fluid leaks which may subsequently appear.
Remember to check that the throttle cable is adjusted correctly and functioning properly, that any disturbed electrical circuits
are operating correctly, that all the nuts and bolts are securely fastened, and that the brakes themselves are operating correctly and efficiently
before the machine is taken out on the road.