Another method of purging brake lines of air bubbles and old fluid is to draw it out under vacuum with a hand-held unit such as the Mityvac, available from automotive suppliers. The process is similar to item 2 except that instead of pumping out the system under pressure from the brake lever, you attach your drain line to a small hand-held vacuum pump that extracts fluid into a clear plastic container. It simplifies bleeding brakes on cars to a one-person process, and even in sleds it can clear air bubbles that otherwise may be hard to purge. Stay Flexible Before bleeding the system, check the hoses for cracks, abrasion damage or hardening with age. If the fluid has become contaminated with oil-based products, hoses can swell internally, restricting fluid movement while looking okay on the outside.
Replacement is cheap insurance.
Some racers like to replace the standard fabric-reinforced rubber hose with braided stainless steel lined with Teflon, for a slight gain in sensitivity at the lever through reduced swelling of the hose under pressure. If you're so inclined, a performance shop can make up custom lines using either replaceable or swaged-on fittings. The braided lines look impressive but can chafe your paint and bodywork at points of contact if not protected with a plastic overlay. Apart from the looks, you're unlikely to find the extra cost produces a matching functional advantage. If you do replace a hose or other hydraulic system component, a full bleeding is the final step in the process.