brake bleeding

[cobra407]

I am still having a difficult time getting my front brakes working. I rebuilt the front calipers and they seem to work well. But I think I still have air in the lines. I used a mighty vac and some teflon tape to seal the bleed screws. There is considerable play in the front brake lever. Are there any other tricks to getting all the air out? Someone mentioned leaving the brakes under pressure over night using wireties. not sure what this does? thanks

[wxp]

I bled my brakes yesterday after cleaning up the master cylinder.  While bleeding them the lever would act as if it was not building any pressure, very little fluid was coming out. got frustrated, tightened everything up to come back to later & they worked just fine. it was weird.

[Rob Valdez 79 R65]

not sure what this does?

Don't ask, just do it.

It was discussed here just recently, I believe.
http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1298745932

[montmil]

As a sidebar note: teflon tape should not be used on motorcycle nor automobile brake line fittings. Small bits of the tape can be cut free by the fitting threads and find their way through brake lines to lodge in a tiny orifice in the master cylinder, or elsewhere, creating an unsafe braking issue... not to mention finding and removing the critter.

Monte

[jamo]

When I rebuilt my calipers with new seals to get then to bleed. I removed them from the forks wedging something between the pistons so they did not move and holding the bleed nipple vertical then bled. Worked for me

[Barry]

I echo Monte's concern about getting PTFE tape in the fluid but admit that I have used it.

When I overhauled my brake caliper I filled it from the bottom up through the bleed nipple using a large syringe. Some sealing tape is needed on the top few threads of the bleed nipple otherwise fluid leaks out. I was careful to keep the tape well away from the cone sealing section of the nipple. It's much easier to push air up than down so this method works well. I didn't have to do any conventional bleeding at all. It did need the lever fastened back overnight though to really firm up.

Not sure I would use this method for a conventional fluid change as the idea is to get the dirty fluid out of the caliper at the bottom rather than push it up through the brake system and maybe contaminate the master cylinder.

[Mike V]

I'll share my frustration with getting my brake system completely bled also.  It did not come easy.  I had completely rebuilt both front calipers (ATE') and a new master cylinder.  The only advice i can bring is; have plenty of brake fluid and patience on hand. I found the purchase of a pair of speed bleeders to be very helpful.

here's the way I tackled it...

I bungeed the left side of the handlebars to the frame to plant the bars stable and getting the bar mounted master cylinder at it's highest point.  Protected the master cylinder with a wrapped wet rag to collect any spillage. Started with the left side caliper alternating to the right.  Slowly depressing the lever and slowly releasing the lever.  I never allowed the lever to fully contact the handlebar - not allowing the MC piston to reach beyond it maximum throw.  Go slow always keeping the reservoir full.  I found the air to get agitated to almost a fine foam.  Occasionally tapping the calipers with a rubber mallet.  I think patience is important to allow the small bubbles to rise and collect, I let the bike sit overnight twice with the brake handle tied engaged to the bar.  I can't explain why this works - but it does.  Finally after almost three days the system became rock solid.  Go slow, have plenty of brake fluid on hand.  Think good thoughts and cross your fingers.  It'll happen.

[cobra407]

thanks everyone. ill wire tie the brake lever down for a couple days

[bruce_launceston]

If none of the above works you probably have a blocked return hole in the bottom of the master cylinder.

The hole is only visible when you remove the plastic reservoir from the master cylinder (there is a screw underneath and an 'o' ring seal).

The hole on mine was blocked solid. It took ages to get it cleared. I used a 0.33mm hypodermic needle as a drill. The hole is about 0.35mm diameter.

As soon as it was cleared all my braking issues went away. Easy to bleed and no more dragging and locking on brakes when hot.

Cheers

[cobra407]

thanks for that info. i was looking for the return hole just the other day. im thinking that might be the problem too

[Lucky_Lou]

I recently fitted a new master cylinder gifted to me (thanks Steve H) i had to clear the return hole before i fitted it, i kept the connecting line upright connected it then topped the cylinder up half way before fitting fitting the M/C piston then mounted it on the handle bar, i figured if i did it this way the system would not need to be bled.....and i was right.
Lou