Back break loosing pressure over time

Dallas · Full Member Joined: Apr 22, 2009 Posts: 34

So Ive bled my rear disk brakes on my 79 multiple times. Im using a pump system to really pull the air out. I will get it to the point where the brake is engaging (albeit not that solidly) and then a half a day later, the brakes have no pressure to them when I press the lever. Where would you guys start? Replace hoses? If so, which ones? Or is there another point of failure I should check first.

Thanks
Dallas

jayel

Dallas wrote:

I will get it to the point where the brake is engaging (albeit not that solidly) and then a half a day later, the brakes have no pressure to them when I press the lever. ............ Replace hoses? If so, which ones? Or is there another point of failure I should check first.
Thanks Dallas

do you see it leaking anywhere? around the calipher?

Dallas wrote:

I will get it to the point where the brake is engaging (albeit not that solidly) and then a half a day later, the brakes have no pressure to them when I press the lever. ............

doesn't sound like you're getting all the air out it should clamp down hard, or has a air leak into the system, old rubber hose(s)? they need replaced...
mikesxs or 650 central

BigGeorge · Full Member Joined: Apr 13, 2008 Posts: 267

Sounds like there is still air in the system or possibly the master cylinder is bypassing internally...... I have had success back bleeding brakes from the caliper bleeder back up through the master cylinder using a lever type oil can (new can that never had oil in it). Fill the can with brake fluid and attach a 1/4" hose from the can to the bleeder using screw type clamps.. Since air wants to rise any air bubbles will go up to the master cylinder..............BG

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

I have reconditioned the caliper and master cylinder and hose's,.................. had the same trouble after i had reinstalled everything, It was a hassle but i removed the rear wheel and unbolted the master cylinder and reservoir, raised the reservoir up as high as i could and wired it so i could remove the cap, twisted the master cylinder so there was no high spots for the air to get trapped in and set the caliper so the bleed nipple was the lowest point..........attached a plastic tubing to the bleed screw and with a syringe pumped fluid into the line ......watching the reservoir at all times...When no more air come out i shut off the bleeding valve, replaced reservoir cap, and reinstalled every thing......................

Dallas · Full Member Joined: Apr 22, 2009 Posts: 34

Thanks for all the replies, I think I am going to order a new steel cable from mikes and go from there. Ill post after I do this to let you all know how it went.

Thanks again

Dallas

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

Thing to remember is..........If you have no leaks, then air is not getting in....... a new hose wont fix it

Retiredgentleman

Dallas;
I would put a re-build kit into the master cylinder.

Dallas · Full Member Joined: Apr 22, 2009 Posts: 34

So Im not sure where to start still. I can find any definite leaks, but it seems like air is the culprit. As for a rebuild kit, I cant seem to find one for the rear, only for the master cylinder on the bars. Im kinda stuck on what to do.

Dallas

Dallas · Full Member Joined: Apr 22, 2009 Posts: 34

I think I might try the technique that 650skull recommended. The only thing that makes me think its a leak is that I will bleed the brake, have brakes for a while, then slowly they will go away and Im left with no back break. Is there a way this could happen without a leak?

Dallas

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

Dallas, go to MikesXS............. Chassis/Brakes..................OEM-Type rear brake parts 70-84.....Scroll down to part #08-0217

Dallas · Full Member Joined: Apr 22, 2009 Posts: 34

Lol, guess Im blind, thanks.

Dallas

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