First published in the February 2009 issue of Street Machine

For your brakes to work effectively there can’t be any air in the system. Loosening a brake line or hose, disconnecting a caliper or changing the brake fluid (an often neglected part of routine maintenance) will allow air to enter the system. Removing that air is a process known as ‘bleeding’.

Bleeding a brake system isn’t difficult but usually needs two people — one to pump the pedal, the other to loosen and tighten the bleed nipples. In a workshop there’s generally someone around to help. But at home, help can be scarce. Under those conditions anything that makes the job easier is a bonus, which is why Solo-Bleed self-closing bleed nipples from Earl’s are such a good idea.

These simple devices eliminate the need for an assistant. A normal bleed nipple (A, above) seals the system by bottoming its conical tip into the seat machined into the caliper or wheel cylinder. Loosen the nipple and fluid escapes around the tip and flows up through an internal passage. Earl’s Solo-Bleed screws replace the solid tip with a spring-loaded floating brass plunger (B, above). Where bleeding with normal bleed nipples requires two people, wth Solo-Bleeds you simply undo the bleed screw about a turn (shown below), then go and gently pump the pedal.

When loosened, the Solo-Bleed spring-loaded tip is pushed down onto the seat, preventing fluid leaking out or air getting in. However, depressing the pedal pressurises the system sufficiently to push the brass plunger off its seat, allowing air and fluid to flow out. As you let the pedal back up, the pressure drops and the Solo-Bleed spring pushes the plunger back onto its seat, sealing the system and preventing air from entering. As with conventional bleeders, attach one end of a tube to the bleed screw and allow the other to drain into a container (shown below) — ideally the hose should be submersed in brake fluid.

Regardless of what’s been disconnected or changed, you’ll need to bleed all four corners. Once only clean fluid with no air or air bubbles is in the system, the brakes are bled. Finish by simply tightening the Solo-Bleeds up with a spanner and the job is done. As you’d expect, they’re a bit more expensive but they take the pain out of this very simple job. They’re available in a wide range of thread sizes and lengths to suit most cars and motorcycles.

While we were at Hoppers Stoppers trying out the Solo-Bleeds, the boys showed us how to make bleeding a brake system easier if you have to fit a new master cylinder. It’s call ‘bench bleeding’ as you mount the new cylinder in a vice and fill it with fluid. Place your fingers over the outlet holes for both halves of the system and use a screwdriver to push the piston into the cylinder (below, left). Because your fingers seal the outlets, when the piston retracts it can’t pull air in from those points. Basically, the only thing it can do is draw fluid from the reservoir. As you pump the cylinder and fluid is drawn in, you’ll feel the pressure on your fingers reduce. When it’s full, pressing the piston will cause only fluid to be pushed out (below, right).

This technique simplifies bleeding a system with a new master cylinder. New cylinders can sometimes refuse to bleed unless this technique is used — what happens is that as the brake pedal is depressed, air is pushed into the system. When the pedal’s released, it simply draws air back into the cylinder. Bench-bleed your new cylinder as shown and you shouldn’t have any trouble. With this technique and Solo-Bleeds you won’t need friends any more!