Norton Commando Workshop Manual

## Brakes, Weels and Tyres

# H

Inspection of Master Cylinder and Components

Discard the primary and secondary cups, the trap valve and boot. Clean the master cylinder and piston in brake fluid or methyl alcohol - do not use abrasive materials or solvent fluids.

Inspect the master cylinder body for wear in the piston bore. Normally, if the seals have been operating satisfactorily no wear need be expected, but if seal failure has occurred, the piston may have destroyed the bore finish. If there is any doubt whatsoever, the cylinder must be replaced.

If the cylinder is found to be fit for further service, ensure the two cylinder ports into the reservoir chamber are perfectly clear and clean. Inspect the hose union and switch threads for clean and satisfactory condition, and the lever pivot bolt bore for wear or cracks, or fractures. Replace the master cylinder if any doubt exists.

Check the brake lever for pivot bore wear and possible wear on the piston thrust face. Replace the lever if necessary. Next examine the piston for signs of scuffing on the ground outer diameters, and any wear on the lever thrust face.

Do not attempt to polish or grind the piston in any way, using abrasive compounds, as the slightest residual trace of such materials, even after intensive cleansing will damage master cylinder and caliper working parts beyond repair, and can result in premature brake failure.

Inspect the brake hose for cuts, signs of leakage or deterioration. Replace if the slightest doubt exists.

Master Cylinder Reassembly

After inspecting and cleaning the master cylinder, clean the piston, spring, spreader and cup washer in clean hydraulic fluid, and place in order of assembly on a perfectly clean working surface, in a dust free room or workshop.

DO NOT USE A FLUFFY RAG TO WIPE THE COMPONENTS. ALLOW TO DRAIN.

Soak the new primary and secondary cups in hydraulic fluid for fifteen minutes, kneading occasionally to encourage the special rubber cups to gain their maximum supple state prior to assembly. Ensure the three relief holes in the "crown" of the piston are clear and clean.

1

Take the "hollow" secondary cup and place it non lipped side against the ground "crown" diameter of the piston. Work the cup over the "crown" by hand, then down the piston body, over the shoulder into its groove adjacent to the main body ground diameter.
CAUTION - Do not use any form of tool to ease assembly of the cup to the piston for fear of damage to the lip.

2 | Fit the boot over the piston open end towards the piston crown and ensure the upper end is fitted squarely and snugly in the piston groove. The piston is now ready for assembly.
3 | Assemble the trap valve to the spring, ensuring the inner plastic bobbin is accurately seated in the rubber valve base, and that the small diameter bleed hole in the bobbin base is clear and free. Ensure the plastic spreader is securely and firmly pressed home on the other smaller diameter end of the spring.
4 | Offer the spring/trap valve assembly into the master cylinder, valve end first, keeping the master cylinder bore upright. It is permissible to hold the nose of the casting securely in a soft jawed vice, provided it is in no way overtightened.
5 | Assemble the primary cup washer into the bore, open end of the cup facing into the bore, followed by the primary cup washer. Ensure only one cup washer is employed at this point. Place this dished primary cup washer, "hump" upwards, towards the open end of the cylinder bore. (The effect of the dished cup washer is to close the primary cup during the return stroke, allowing oil to by-pass the cup and replenish the pressure cylinder).
6 | Offer the piston crown first into the cylinder. Place the 10 eared boot circlip over the top of the boot, the slight set on the ears facing away from the cylinder. Ensure fluid is smeared onto the secondary cup and into the mouth of the cylinder bore.
The next series of operations, to locate the piston, boot and circlip by means of the brake lever and pivot bolt can be difficult without the aid of special tools, and the assistance of a second operator. However, if care is taken, assembly can be completed without such help, the difficulty being to locate the base of the boot into the cylinder counterbore and finally locate and snug home the circlip whilst holding the piston assembly within the bore of the master cylinder, against the trap valve spring, long enough (and with sufficient piston thrust pad clearance) to be enabled to fit the hand lever and to locate it with the pivot bolt. The method of assembling these parts is detailed below:

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