ABS Disk Brakes/Bleed/Restore Pressure By grbell1834 (Read 7,339 times)

[grbell1834]

I am having trouble restoring the pressure on both front and rear disk brakes.
I am at my wits end on trying to get the air out of the lines.
I have gone thru numerous bleeds and refills, appears to be clean, free of air brake fluid, and cannot build pressure on the brake pads. I've taken all apart, including the ABS pistons. the little piston element inside the ABS cylinder appears to be working ok. I've taken the caliper off, applied air pressure, and the cylinders that move the pads, work fine, not bound or held. I've replaced the piston element inside the master cylinder. I've watched the video on line and have done all, except I have let the fluid levels go to empty in the master cylinder. I fill, purge out fluid at caliper valve until all air bubbles gone, and just clear fluid in plastic tube, close relief value, and cannot get pressure to build. Have tried two different brake fluids to no avail. What does anybody suggest?

[JR]

I had the exact same thing happen to me on my 150, like to have drove me nuts! I use the Prestone DOT3 synthetic fluid and I bled and bled and bled, finally I left the cover off of the fluid reservoir and just let it sit awhile open with plenty of fluid in it. I worked around the house some and would go back and just slowly pump the handle back and forth a few times very slow and each time I would get onoe or two tiny bubles come out.

After about 6 hours of this again just as I worked through the day the brake started getting hard and pressured up, put the cap on and all is well. Don't know to this day what it was other than the smallest amount of air?

JR

[justbuggin2]

when replacing a master cylinder it is recommended to bench bleed it before putting it on the car . when you let the cylinder go dry it got air inside of the mastercylinder as you try to bleed it out at the caliper you will get so much of the air out there will be some air the stay in the m.cylinder that will not go out through the line to the caliper . as jr said leave the cover off and very slowly work it until you see no more air bubbles in the master cylinder. after that check at the caliper these things dont move very much fluid at a time

[n4zou]

First thing to do is pull the bleed nipple out of the wheel cylinder and wrap a couple of turns of Teflon pipe tape around it. Don't cover up the little hole with tape! Air can sneak back in around the threads and the pipe tape prevents that. It also prevents the threads seizing up in the cylinder threads so the nipple will turn freely the next time you need to bleed the system. You also must have a tube and a bottle connected to the nipple. Put a little brake fluid in the bottle so the end of the tubing is flooded. The bottle must be below the brake cylinder. This acts as a check valve so air is not drawn back into the nipple and cylinder as you bleed it. Fill the master cylinder with brake fluid, put the bellows back in the fluid reservoir, and attach the cap. I don't understand why it's necessary to cap the reservoir but I've never successfully flushed all the air out of these brake systems without doing it. Yes, it's a pain in the ass but if you don't do it you'll never get all the air bled out of the system. On front brakes with the anti-lock device air can hide in the anti-lock device. You can flush it and it feels normal but a few days or even a couple of weeks later the air comes out of hiding in the anti-lock device and you'll need to flush it again to remove that last tiny bit of air. I've made it a policy to bleed the brakes on these little buggers once a year flushing out the old brake fluid. These systems are so small even a little moisture or other contaminates can quickly degrade performance.

[grbell1834]

Thanks for the response on the brakes. I've been gone the last week or so and unable to try these attempts at fixing the problem with the air in the system, but will do so in the next day or two. The problem I had was with the brakes going soft, because I let the old fluid remain too long and it must have attracked moisture and got contaminated. I didn't realize this would be such a problem to replace and re-pressurize. Truly, what a pain in the butt.

[grbell1834]

n4zou
I am assuming with the line off the nipple to a bottle below the caliper, that the tube itself will never completely fill, unless the bottle were to completely fill? Otherwise, I have gone thru the procedure as you have suggested, by taping the nipple, attaching the tube to a collection bottle, flooded the end of the tube in the bottle, etc. I get a few major air bubbles in the beggining, followed by some very tiny tiny small ones, etc. After the evidence of the tiny ones seems to dissapear, I cannot seem to get even the fluid out of the tube at this point, and of course no pressure builds. Still perplexed!!

[grbell1834]

Now I've tried this proceedure at least three times with filling the master cylinder, bleeding all apparent air, squeezing brake lever very very slowly to just brake fluid in bleeder line, with the master cylinder cover/gasket/plunger in place and tight. Close the nipple tight and cannot build pressure on the caliper. I don't get it???

[JR]

I remember when mine doen this I filled the master cylinder, put the cover on and pumped it very fast untill it finally started building pressure. Waited a spell and came back and repeated. Then I pulled the top back off put a tad of fluid in and she finally worked with no issues.

JR

[grbell1834]

I've attempted fast pumps, slow pumps, waiting, etc. Cannot build the pressure. I get nothing but clear fluid in the bleed tube and no evidence of any air. The nipple is at the highest point of the caliper, so the the brake fluid makes it course from the master cylinder, thru the line, thru the ABS device and into the caliper. The fluid must fill the caliper before it would find its way out thru the nipple. It would only make sense at this point, and no evidence of any air in the bleed tube, that the pressure should build in the caliper, push the pistons out and appply pressure to the pads and close on the rotor, however this does not happen. I might have to resort to a bike shop, however I've contacted a few and they refuse to work on Chinese made bikes. Is there anybody in the Tampa area that could make a recommendation for servicing these brakes?

[grbell1834]

Does anyone understand the ABS piston and how it works? I took off and took apart. One removes a cap on the bottom which exposes an allen head bolt which puts pressure internally on a piston and spring. When I cleaned and put back together, I thought I tightened or returned to the original position. Is there anyway to set this? Can this be the reason I cannot build the pressure on the caliper? Probably should not have nuts with this to begin with, but there was some crud and build of old fluid on the internal piston and spring, which I thought might be imparing its function?

[grbell1834]

Just thinking what the concequence might be if I removed the internal piston and spring of the ABS device? If its a working brake vs ABS brakes, that would be OK by me. This ABS claimer is really not ABS like on a car for these bikes. From what I read its a basically a hydraulic limiter to prevent the brakes from locking. Right now, I'd be happy with any kind of braking.

[JR]

I'm thinking your master cyclinder is shot and needs to be replaced?

But here is a breakdown of the ABS system;

[grbell1834]

Two things. Have any idea how that allen head screw, or the adjustment screw is set? This regulates the force on the spring and intern the same force on the piston. There is quite alot of travel and subsequent threads on this adjustment? Got any thoughts as to what be the issues if the spring and piston were removed?
I have already replaced the master cylinder pistons, as I thought the former might have had worn seals. This fix unfortunately didn't help, and as a result probably didn't need to be replaced.
Thanks for all your help.

[JR]

I don't have a clue? Can you hook them direct without the ABS? This would at least tell you if it is the ABS and if not then if you've reworked the master cyclinders then it's got to be the brake calipers?

JR

[grbell1834]

Thanks for the info on the bake caliper. I removed the front brake caliper and forced pressurized air into it, and discovered that the pistons were difficult in moving. You can remove the ABS device and expose that threaded hole, and force air into that if you have a rubber nozzel on the end of the air gun. I had to increase the pressure up to 100psi before I got the pistons to blow out. I don't know for sure if its just been been for sitting sometime, but the internal seals seem rather dry, so I lubed them up a bit with some brake fluid, put back together and made sure they were working freely, and set them so there was just enough clearence in the brake pad opening to slide over the rotor. I re bled the line and the master cylinder, removed any and all air, and wah lah, pressure finaly built on the brake lever, and now have adequate braking to stop this freaking bike. I wanted to try this with the air thing before investing $65.00 in a new caliper. I thought I would elaborate on this some in case some others ever run into this issue. Thanks for you patience and all the help.