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How to… service a motorcycle brake master cylinder

Keep old stoppers sharp

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Submitted by Visordown on Thu, 02/11/2017 - 12:29

How to… service a motorcycle brake master cylinder


Words and pictures by Alan Dowds

BRAKES come in two halves (well, three halves with an ABS system). The bottom half tends to get all the attention in terms of maintenance: pads and calipers are regularly changed, cleaned and primped, hoses are swapped for steel braided chappies, discs get checked for wear. But up top, at the master cylinder on the bar, not much tends to happen. You open it to change the fluid, and if you drop the bike, you'll replace the bent or broken lever.

Check the service manual though, and you'll see that the master cylinder has seals inside that should be checked and changed. It's a simple piston with two rubber seals that runs inside a cylindrical bore – but the seals do wear over time, and replacing them can often sharpen up old, limp stoppers.

Here's how to rebuild a basic brake (or clutch) master cylinder in five easy steps…

1. Get it off

We'll assume you're comfy enough with gentle spannering – so removing the master cylinder shouldn't be a big deal. Loosen the bolt (banjo type) that holds the hose on first: it'll be tight and a bugger to unscrew once off the bars. Watch for leaking brake fluid: there'll be a fair bit, and it's nasty to paint and plastics. Use plenty of kitchen roll or shop towel to catch drips, and wash off any excess quickly with some water. Careful though – don't get water into the brake hose itself.

Next, unbolt the lever. There'll be a nut on the bottom that comes off first. Then unscrew the bolt through the lever pivot. Again, this is easier with it still on the bars. Then loosen the two clamp bolts holding the master cylinder to the bars. Find the brake light or clutch switch connector, disconnect the wires, and the cylinder should just lift away. Secure the brake hose so it's not going to leak fluid anywhere.



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