Replacing Brake Lines, Fluid, and Bleeding
Replacing Brake Lines, Fluid, and Bleeding
Motorcyclist Magazine August 1995
If you're after optimum braking performance, old brake hoses should be replaced. They become flexible as they age, introducing a spongy feel. There are a number of good aftermarket lines, either with braided stainless steel or Kevlar sheaths. Both types will provide a better feel over a longer life than the original-equipment rubber lines.
A variety of aftermarket brake lines are available from companies like Lockhart -Philips, Goodridge, and Russell. Before embarking on a brake line replacement mission, make sure the lengths of line you've acquired match the ones you'll remove, unless you are also changing some related components like the handlebar, in which case you'll need a different length than stock.
In order to install new hydraulic brake lines, all old brake fluid must first be flushed out. Siphon, soak or scoop out as much fluid as possible from the top of the reservoir before proceeding. Make sure there are no particles in the reservoir itself that might signal a corrosion problem and could end up jamming a caliper piston and causing a crash. (If you find any grains of metal, plan on rebuilding the entire system.)
Before removing the top of the brake fluid reservoir, use rags to protect the surrounding area from dribbling brake fluid. Keep a can of contact cleaner on hand to quickly wash away accidental spills on uncovered parts. Brake fluid attacks many surfaces, especially paint. Wear protective rubber grooves when things get dirty to spare your skin from contact with all manner of motorcycle gnarliness.
Attach a section of hose to the bleeder on one of the calipers (see photo). Loosen the bleeder nipple, then either fire up your power bleeder like a genuine professional mechanic or pull in/push down the brake lever to begin flushing fluid. Before releasing the lever, retighten the bleeder to prevent fluid from re-entering the system. Do this repeatedly (loosen/activate brake/tighten/ release brake, and so on) until the brake master cylinder is sucking air.
When draining brake fluid or bleeding brakes, always use a section of hose - preferably clear- to control squirting and monitor progress. Also, before detaching a caliper for rebuilding and/or replacing brake pads, do yourself a favor and loosen the pins(s) holding the pads in place.
Once you are satisfied you've gotten all the fluid you can out of the system, it's time to start putting new lines on. Pay close attention to duplicating proper line routing. Discard the metal crush washers from the old brake lines and install new ones. Once all updated segments are in place and you've double-checked the tightness of all fittings, it's time to add new brake fluid. Follow manufacturer's guidelines for the proper type of DOT brake fluid for your bike. Take care not to spill when filling the reservoir.
We cut the rubber guide cushion off our old lines with a razor blade and squeezed the stock fitting over our new lines to make routing easier. Use caution when installing steel lines; if they rub against other bike parts, their abrasive nature can eat right through bodywork or electrical parts and such. Plastic spiral wrap, clear tubing or heat-shrink tubing enclosing braided lines can alleviate this problem. Kevlar lines should be protected as well, as it's possible to rupture a Kevlar line through continuous rubbing.
Make sure you have your calipers attached with pads in them before continuing. Without a power bleeder, you'll have to use the "loosen bleeder/activate brake/tighten bleeder/release brake" method of introducing new fluid to the brake system. Be patient and monitor the hose coming off the bleeder. You should be able to eventually feel fluid pumping into the caliper and then visually confirm this as clean new fluid pumps through the tubing exiting the bleeder. Check the level of fluid in the reservoir frequently and keep it filled to make sure air isn't pumped into your system from an empty master cylinder. Continue this process with each caliper until there are no more air bubbles emanating from the calipers.
At this point, make sure everything is tight and activate the brake lever. It should feel stiff and firm. Any mushy feeling indicates the need for additional bleeding. Fi]l the brake fluid reservoir to just below the indicated level to accommodate fluid swelling in hot weather as this can lead to a seized brake. Also, if new brake pads haven't been installed, a filled-to-the-rim reservoir won't allow the caliper pistons to be pushed back at a later date because the fluid will have no place in which to expand. Replace the reservoir top and you're ready to go. And stop