Motorcycle Repair: honda 1994 cbr brakes., bike brakes, vacuum pumps

Question
I have been outside all day, changed both tires and other misc. stuff, but I can't get my rear brakes to work again. I have bled them and made sure all parts are still on everything, is there some sort of trick to doing bike brakes? Most of my mechanical experience is with cars so I am unsure about some stuff. I used dot 4 fluid and belive I did it all proper. So if you could maybe give me a step by step so I can see if I did something wrong. I pumped the break with it off the tire and the caliper was coming out.

Answer
Jason, it doesn't take much to get air into the brake system and it can often be a chore to get it back out again. See below links...

http://www.totalmotorcycle.com/maintenance/brakes.htm
http://www.motorcyclecruiser.com/tech/brakeserv04/
http://motorcyclistonline.com/howto/122_0306_howto/

The small bleed ports in the bottom of the cylinder have to be open and if you had dirty fluid in there and then things got moved around during your wheel/tire changes, then some crud may have gotten into the rear master cylinder bleed ports.

If you hit the brake pedal enough to move the pistons out too far, they may have been exposed to air, momentarily.

You may have to try to remove the caliper, lay it down on the floor so air bubbles will travel UPWARDS and try to bleed it in that condition. You will have to put a hammer handle or something sturdy in the caliper to keep the pistons from coming out while you bleed the system again.
If there are any hydraulic connector joints in the system, you may try to bleed the air from the connectors, as well as the caliper. Vacuum pumps usually do a pretty good job of sucking air bubbles through the system, used correctly.

I couldn't find one site I often recommend, but they used a coil of clear tubing, headed into a small container with a couple of inches of fluid in the container. With the line hooked to the caliper bleeder, pump fluid through the system, so it goes into the submerged end of the tubing in the container. This will keep the air from being pulled back into the system, as you pump the brake pedal. Remember to keep the reservoir full, as it drains in a hurry, due to the small capacity.

Bill Silver