Pump up your brakes

Take the tedium out of bleeding by deploying a vacuum kit

1

Weapon of choice

Your bike’s brake fluid needs replacing every two years. Now, unless your machine is religiously dealer serviced, chances are the golden stuff in your brake lines is well past its best and needs replacing. It has the potential to be a horrible, messy job but there’s one piece of kit that makes things easier: a vacuum pump. Here’s how to wield it…

2

Check the wear

A decrease in the reservoir fluid level can indicate that your brake pads have worn below the specified service limit. Remove the caliper and turn it upside down to get the best view of the pads, replace them if they are worn below the service limit. As a general guide there needs to be at least 1mm-1.5mm of material to be safe, although this varies according to the type.

3

Get everything covered

You need to take care because brake fluid has a corrosive effect on painted and coated surfaces, so shroud the tank and headstock area with a workshop cover to protect against possible spillages. Always have a few sheets of workshop paper towel to hand ready to mop up any drips that find their way on to unprotected areas.

4

Access the fluid

The old brake fluid needs to be flushed from the system. To do this, undo the master cylinder reservoir lid and carefully remove the rubber diaphragm. Sometimes it will stick to the reservoir body, if this is the case gently ease it off and have paper towel to hand to catch any drips and make sure they don’t find their way onto your paintwork.

5

Connecting the bleed kit

Identify the size of the spanner needed to fit the bleed nipple on the caliper, they are usually 8mm–11mm. Remove the rubber grommet protecting the nipple. Place a ring spanner on the nipple so it can be loosened around 90 degrees. Fit the pipe from the bleed kit to the exposed nipple.

6

Draw out the fluid

Pull the lever on the vacuum pump a couple of times then unto the nipple until the vacuum starts to draw the fluid out of the caliper. As it appears in the tube it will flow into the pump receiver, so keep pumping and maintaining the flow. Top up the master cylinder reservoir with new fluid.

7

Gold and brown

Continue to add brake fluid to the master cylinder as the reservoir level reduces, you will find it will drop quite quickly as the old fluid is drawn out. You’ll notice a change of colour in the fluid as the new fluid is flushed through into the pump receiver as the old fluid will appear browner. At this point, tighten up the nipple and connect the vacuum pump to the other caliper.

8

Empty and repeat

Before you start pumping out the other caliper, empty the old fluid out of the pump receiver then refit it to the pump and make sure it is sealed correctly. As before, give a few pumps to build up a vacuum then crack the nipple until fluid appears. Keep pumping and topping up the reservoir with fresh fluid until the new liquid has drawn right through.

9

Easy bleed

Provided you haven’t let the reservoir run dry at any point, using a vacuum bleed kit like this means there is very little chance of any air being trapped in the system, leading to a spongy feel at the lever. Tighten the nipples up, pump the lever to assess feel, it should be firm, then top up the fluid to the upper level and carefully replace reservoir diaphragm and cap.

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If replacing fluid in a dry system…

If you’re refilling with fluid after you’ve fitted brand new lines or freshly rebuilt calipers you will see the pump pulling out plenty of air bubbles. As the pump pulls down fresh fluid the bubbles will diminish. You will need to swap between left and right calipers two of three times to ensure that the fluid is being pulled though evenly.