How to service your brakes

Sharpen up your stoppers with a master cylinder rebuild kit

Time for a rebuild? 1

Your front master cylinder is a basic hydraulic pump which provides many miles of maintenance-free use. But over a long period of time the internals can become worn or start to perish, resulting in fluid leaks, soft lever feel and poor brake performance. Luckily it can be fixed with a rebuild kit, which can bought from your dealer.

Remove from the handlebar 2

Begin by undoing the banjo bolt that connects the hose, then disconnect the brake light switch connectors. The front brake lever also needs to be taken off, so undo the bolt and put the lever to one side. Undo the two bolts that secure the master cylinder to the handlebar and the whole assembly should come off.

Clean it up 3

Put the master cylinder into a tray while you work on it. Undo the top of the reservoir and dispose of the remaining fluid. Give the rest of the master cylinder a good wipe and clean with contact cleaner to remove dirt and all traces of brake fluid. Give the rubber diaphragm an inspection and clean in the same way.

Reveal the plunger 4

Aside from the lever, the master cylinder only has two moving parts: a spring, and plunger, with seals attached at each end. To gain access, you first need to remove a rubber boot that protects the plunger from contamination, this can be pulled out with pliers. Behind that is a circlip which needs to be pinched together and pulled out. It’s tricky so take your time.

Extract the plunger 5

Once the circlip has been removed, use pliers to extract the plunger; it should come out easily but be sure to do it slowly, as there is a spring and washer that could fly out with it. Lay all of the parts out in sequence then make sure the new parts correspond with the old.

Clean the bore 6

The next step is to make sure that the bore of the chamber is free from debris or contamination. Give it a thorough clean with a contact cleaner, ideally find a brush small enough to help. When you’re satisfied that it’s completely clean, give it a final blast with an airline.

Clean your area 7

Before you start assembling the new plunger, remove all of the old components from the tray keeping them in the order that they were removed. Clean the tray with contact cleaner so there is no trace of old brake fluid or debris. Make a final check that all of the new parts are there and are going to fit. Make a note of the correct way the spring is fitted as it is tapered.

Slide in the seals 8

Carefully fit the new seals, they are sided so will only work if they are fitted correctly. You can assume the old ones were fitted correctly, but just to be sure the open ends should face the bottom of the chamber. Fit them carefully with as little distortion as possible. The seal next to the spring on our kit has a shim fitted behind the seal.

Correct clip 9

Insert the plunger into the bore with the spring fitted the correct way. You will then need to fit the new circlip, but identify which way round it goes before you put it in as there is a sharp, angled side and a rounded side. The sharp edge has to face away from the body of the master cylinder so that the sharp edges grip tight into the circlip groove.

Rebuild and refill 10

Finally, slide the rubber boot over the plunger before refitting the master cylinder to the handlebar and reattaching the banjo using the copper washers. Fit the brake lever then top the master cylinder up with fresh fluid. Bleed the system by pumping the brake lever, hold it in then crack the banjo bolt to release air until there is feel at the lever.