Can't bleed brake

OK, here is an odd one. I have done every technique to bleed my front disk brake...tube from bleed valve under brake fluid and pump/bleed/pump (get tiny, mist-like bubbles pushed through the clear tube)... push caliper in and pump back to force air up to the MC and fluid back down. Rebuilt the caliper, good MC and brake line, new crush washers, afraid to tighten the bolts more, no apparent fluid leaks. Each individual part seems to be airtight. Took it, all together: MC/line/caliper to Dean, my used parts guy and all around good mechanic. He played w/it for awhile and got the pumping action hard. Looked at me like..."why couldn't this guy get it bled correctly". Took it back and installed it, keeping everything together. Pumped it up and it's mushy. Basically when the system is all horizontal it pumps hard, when the caliper is below the MC air gets into the system and it gets mushy. Could it be the bleed valve? Any thoughts, where is the air getting into the system???
Thanks
Ron

Warped/dished disc?

Hey Lorcan, congratulations on the speed record!!! Thanks for the reply.

Lorcan wrote:

Warped/dished disc?

The disc does have some surface rust. It hasn't been miked but it doesn't look like it's warped or so thin that the caliper pushes out too far. The caliper piston looks real good, also, no pits or corrosion. It also acts the same way w/the caliper off the disc and I'm using a board or c-clamp to prevent the piston from pushing out too far. Doing this I can actually see the piston pulsing. When I pump and hold the brake lever, I can see the piston put pressure on the board or clamp but then releases before I've released the lever.
Ron

bad wheel bearings can cause a mushy feel. but only while riding.

if its mushy at a stop, try bleeding at the line connectors. you open and close them while pumping, just like the bleed valve. often theres an air bubble right at the junction.

Not too sure about Your bike,but on My 77 1000,I had to remove the calipers(when I did My dual caliper conversion),and tilt them upward to get the last of the air out of them.When they were on the bike,just that certain angle was preventing the calipers from bleeding out all the way.(trapped bubble)
I know Others who had to do the exact same thing to get Theirs done properly.
It worked.
It only took Me about 3 days of pulling My hair out,to discover this!:pinch: :woohoo:

Here's some more info...



kzrider.com/forum/viewthread.php?tid=24892

Do a search in the archives...lots of great info there too.

Thanks for the replies Nelson and Sandy,
Nelson, Good thought but I have a single front disc system so there is no junction.
Sandy, Thanks for the information thread. In a perverted way, it's reassuring that everyone seems to have bleeding problems and gives me hope that I do not have an invisible leak. Other than the vacume fill I've tried most of the techniques mentioned. Although I did something similar, to the caliper higher than the master cylinder technique, I'll have to try it again. Like I said w/the system off the bike and completely horizontal, I can get decent pressure in the lever, but when I lower the caliper below the master it gets mushy. I'm about ready to take the system to a shop and have them do the vacume fill. I haven't tried teflon tape around the threads either.
Thanks again and those posts have given me much food for thought.
Ron

It could take a few hours and a bunch of pumps .
You can also take the mc cover off and open the bleed valve the let it set. it shouldn't take to long for fluid to come out the bleed. Make sure you have a hose on it. Don't pump just watch. When it starts to run do not run low on fluid

when I went to a new brake line I had the same problem. What you need to do is loosen the banjo bolt on the caliper (yes I said loosen) just a bit and pump quite a few times then when you see lots of fluid coming out of the bolt and all over evrything tighten it up and then try and bleed the brakes. It sound odd but it will work.

I wanted to update y'all on my progress. Sandy, rgpbeme and jailbait. I tried all of your methods. I tilted the caliper so the bleeder valve was at the top, a big bubble came out. I also let it drip from both the banjo bolt and the bleeder valve. I do have positive results. The brake is much firmer but to me it is still a bit mushy, but driveable. I'm starting to think that the hose is "pulsing". My old brake line has been deteriorating for the past 24 yrs and I think it is just not holding the pressure like it should. My parts guy is getting me a new stainless braided line (cheap) and has promised me that after he puts that on I won't have any problem. At this point that's the way I'm going to go, I'll let y'all know how that goes.
I want to thank everyone for their suggestions, I really appriciate it .
Thanks
Ron