Reverse Brake Bleeding

Do it backwards like the Pros do!

If conventional brake bleeding of the front brakes is leaving you with less hair and more wrinkles between the eybrows, try doing it backwards, like the professionals do!! If you have opened the system by changing brake lines or working on the calipers or the reservoir, this may be the only way to completely rid the system of air.

Pro shops use a pressurized or "Bladder" setup to simply fill the system from the bottom up, chasing the air upwards, out the top, then some of the fluid is drawn back out or pumped back out to eliminate any residual air that may be pocketed in any upper recesses of the caliper.

With a few dollars and a trip to your local hardware store and kitchen, you can build your own "Gravity Bleed" system and do the job right the first time and be finished in an hour, instead of a week!!

Think of this system as a medical "I.V." system, just like the one they give you blood or fluids with. You fill a reservoir with fluid, attach it to the caliper bleeder valve (nipple), then either let gravity do the work, or lightly apply squeeze pressure by hand. Very simple, and extremely effective.

Some items you will need:
1.) A typical 16 or 20 oz water bottle, clean and dry.
2.) A 3/16" Brass Hose Barb from the hardware store (with 1/8" pipe threads on the back end).
3.) A 1/2" brass Lamp base nut (listed with 1/8" ISP threads (to secure the hose barb with.)
4.) Two used banjo crush washers (these are a perfect size, but other washers will work.
5.) 6 feet of 3/16" inside diameter clear tubing.
6.) (Optional) 1/4" outside brass needle valve.
7.) A roll of Duct tape and a Coat Hangar or rope for suspending the bottle.
8.) Turkey baster (for removing excess fluid from reservoir.
9.) Some Teflon plumber's tape for sealing the bleeder valve threads.

Drill a hole in the cap of the water bottle and attach the hose barb to the cap, using the brass lamp nut and the two used banjo washers. wrap a loop of duct tape over the bottom of the bottle so you will have something to hang it upside down by.

Pour in the brake fluid. Attach the clear tubing to the cap. (I used a small needle valve near the free end of the hose just to make things work a little cleaner, since I had to bleed both sides of my dual disc system, but the needle valve is not necessary.)

Remove the caliper bleeder nipple, clean its threads, and then wrap a short length of Teflon tape around the threads to help seal it from air entry or fluid leakage during the process, then reinstall the nipple to the caliper.

First of all, use common sense when setting up to bleed. Air migrates upward in a liquid system, so tilt your handlebars, turn your handlebars, and or reposition your master cylinder so that the banjo fitting is BELOW the lowest point of the reservoir.

Now, after removing the reservoir cap, loosen the caliper bleeder valve to open it, and attach the free end of the clear tubing to it. It helps to let the clear tubing fill up with fluid right to the end before attaching to the bleeder valve, just to reduce the introduction of air into the brake system.

Raise and secure the upside down bottle to a level just above the reservoir, then take a small pointed punch or other device and poke a small "breather" hole in the bottom of the bottle (which is now the high end), so it can draw in air as the fluid flows downward. Make sure that the clear tubing makes a constant uphill path to the bottle so that air in the tubing will work its way to the top and into the bottle.

You can help and speed the process by taking the bottle in your hand and while holding your thumb over the breather hole, squeeze the bottle gently, and watch the reservoir as it fills. You can also "suck" fluid back through by moving your thumb off the hole, then squeezing the bottle to remove its air content, then hold your thumb over the hole and manipulate the bottle to draw fluid back in with a slight vacuum pressure

When the system is initially filled with fluid, let it sit undisturbed for 15 minutes, then there will be three air bubbles left in the system. One small one just below each bleeder nipple at the calipers, and one big one at the master cylinder banjo fitting.

Now, with the system full, you can "tickle" that bubble out of the banjo by LIGHTLY squeezing the lever only a SLIGHT amount (may 1/4"). Just "wiggle" the lever in and out at the very outward portion of its travel, and it will draw that bubble upward. If you fully squeeze the lever, or squeeze it hard, you are forcing that banjo bubble down into the brake line, and it has to start climing back up all over again.

When you can't "tickle" any more air through the tiny orifice in the reservoir, reverse sqeeze some more fluid through the system with the bottle, and watch for any new bubbles. If you don't get any new ones, and can't "tickle" any more out from the top, then crack open the caliper bleeder and SLOWLY bleed any remaining caliper air out from the bottom conventionally. Finish off the other caliper and test the system.

Dual Disc Notes:

If your system consists of dual brake discs and calipers, work the left caliper first, until fluid begins to reach the reservoir, then swap over and work the right, until all air is evacuated, then finally, go back and lever bleed the left again to make certain there is no air left in the caliper itself.


Mocc's Place