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rear brakes nightmare

  • Thread starter Thread starter SeanMora77
  • Start date Start date
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SeanMora77

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I've dis-assembled the rear caliper, cleaned and rebuilt. Same with the master cylinder and I cannot get any pressure to build. I've tried every method Ive found on here to bleed them and nothing is working. At best I can get the pads to pinch the disc for a millisecond which stops the wheel when hand turning it, but on the road it isn't effective at all. HELP!
 
It sounds like you have an air bubble or two trapped in there.

Tell us about how you tried to bleed them.

When bleeding my rear calipers, I used a combination of suction (via a large medical syringe and length of fuel line) and pumping the brake pedal. Remember that there are two bleeder screws and that it's generally easiest to bleed the one farthest from the MC first.

If you can't get any fluid to move through the system when pressing the brake pedal, you have to "prime" the MC by sucking fluid through from the bleeder screw.
 
I've been bleeding the one closest to the MC, I'll try to bleed the other one first. I removed the caliper and brake line from the frame and elevated them higher than the MC thinking gravity would help remove all bubbles with no luck. Also tried applying suction.
 
Out of curiousity, Sean, what parts did you use in your rebuild?

OEM or aftermarket (e.g. K&L)?
 
Air bubble for sure man...crack the bleeder and let gravity do the work. Wait till the fluid pours out without bubbles then tighten. You may have to reopen the caliper and grease it
 
May help to prime the master cylinder. Drawing vacuum on the bleed nipple usually gets the system primed adequately. The other thing is to make sure all the small passages in the master cylinder are open. If the prime business doesn't get it done, I'd take the master apart again and double check everything.
 
The MC rebuild kit was purchased from Z1. I just tried the bleeder screw closest to the rim and still no results, although I did see a few bubbles break loose. I have taken the MC apart three times now, triple checked the order of assy to be sure. Cleaned the small holes out spotless... the only thing I have not replaced are the crush washers on the banjo bolts. Could this be a part of the problem?
 
If the crush washers are no good she'll be leaking brake fluid at the seal - it's obvious.

Did you remember to replace the little seal that sits in between the two halves of the caliper?
 
No leaks anywhere, and yes I did replace the seal between the two halves of the caliper.
 
SeanMora77 said:
No leaks anywhere, and yes I did replace the seal between the two halves of the caliper.
Click to expand...

Are your calipers and master cylinder working well enough that you could drain the master cylinder a few times when you are bleeding it? Take the top off the master cylinder and keep a bottle of fluid handy, refill the master cylinder before it empties as you are bleeding the brake.

If you're not building enough pressure consistently to drain a couple of bowls of fluid, there's probably something wrong more than just air in the line.

If it is just air in the line, it's a pain, but unbolt the caliper and get it higher than the master cylinder and try bleeding it that way.
 
Do you have any pressure when you depress the brake pedal?
I loosen the bleeder before I depress the brake, once I depress the brake pedal I hold it down and tighten the bleeder (so it can't suck air back in) before I let the pedal come back up and keep repeating this until I get all the air out, all the while keeping the fluid in the master cylinder reservoir at the full mark.
 
sedelen said:
Do you have any pressure when you depress the brake pedal?
Click to expand...

Yes, I think we need to know what the pedal feels like to debug.

How old are the brake lines? They could be constricted and preventing the air from moving to the caliper.

Maybe disconnect the line at the caliper and see if the MC can push the fluid through the lines.

Maybe try reverse bleeding with a a syringe. I have found this a good way to get the air out of MCs.
 
I can get it to the point of slight pressure, but the brake lever still bottoms out. I suspected a faulty brake line so while I had everything apart the other day I blew some compressed air through the line. Brake fluid is getting where it needs to go. I will be replacing the line soon, but I don't think there is anything wrong with the one that's on there. If I unscrew the bleeder before I depress the lever brake fluid spurts out as it should. I'm at a loss here guys, I rebuilt the front brakes and they are spot on, perfect. I'll get back to it later today and post results. Thank you all
 
Is it an OEM rubber brake line? I've read that these can develop weak areas over time that are hard or impossible to see and start to flex when the brake is engaged. (Probably why Suzuki wants to change them out every two years.)

After having used teflon/stainless steel lines, I will probably not own a bike with anything else.

The MC could still be suspect since it's not fully OEM. K&L kits have a reputation of mediocre quality.
 
SeanMora77 said:
If I unscrew the bleeder before I depress the lever brake fluid spurts out as it should. I'm at a loss here guys, I rebuilt the front brakes and they are spot on, perfect. I'll get back to it later today and post results. Thank you all
Click to expand...

You shouldn't have any pressure built up in the line until you depress the brake pedal, sounds like your caliper piston is stuck if it is indeed "spurting" brake fluid when you loosen the bleeder without depressing the pedal.
 
I wrote that wrong. Fluid doesn't spurt out until I depress the brake lever.
 
SeanMora77 said:
I wrote that wrong. Fluid doesn't spurt out until I depress the brake lever.
Click to expand...

OK then, try to bleed them, put a little pressure on the pedal and open the bleeder a little then push the brake all the way to it's stopping point, once there tighten the bleeder and let the pedal come back then do it all again until you get all the air out.

Once you feel confident you got all the air out through both bleeders, press down on the brake and see if the caliper closes.
I had a stuck piston on my front brake once, I squeezed the lever and whacked the caliper with a rubber mallet. Actually that worked.
 
I'll give it a shot. I'm confident that the pistons aren't stuck because I popped them out with compressed air when I rebuilt them, and scoured the gunk out of the caliper. If I remove the dust cover from the top of the caliper I can see the pistons actuate when I move the brake lever.One thing I did not do was replace the piston seals. I removed the old ones and cleaned the groove they sit in and put them back in. Is it possible they are too worn to offer the resistance needed? The only reason I reused them is because they looked fine after I cleaned them and I read that there is really no need to replace them.
 
SeanMora77 said:
I'll give it a shot. I'm confident that the pistons aren't stuck because I popped them out with compressed air when I rebuilt them, and scoured the gunk out of the caliper. If I remove the dust cover from the top of the caliper I can see the pistons actuate when I move the brake lever.One thing I did not do was replace the piston seals. I removed the old ones and cleaned the groove they sit in and put them back in. Is it possible they are too worn to offer the resistance needed? The only reason I reused them is because they looked fine after I cleaned them and I read that there is really no need to replace them.
Click to expand...

I would think if they were bad you'd be leaking fluid.
 
Somehow we got to isolate the function of the master cylinder and the caliper.
If you can get a steady flow of fluid from the bleeder and you pump the brake it would seem to me the master cylinder is pumping, and when you tighten down that bleeder screw you should have some pressure there.
So if you have the bleeder screws closed and pump down and hold it and loosen the screw it should be under some pressure when you loosen it.
If you're confident it's working then you need to look at the caliper, the pistons, the pad installation, could be binding mechanically.
Perhaps something in the links below will help sort things out.

http://members.dslextreme.com/users/bikecliff/images/bleedbrakes.pdf

http://members.dslextreme.com/users/cbsaunders/gs/79-Brake_overhaul.pdf

http://members.dslextreme.com/users/storagecliff1/images/brake_caliper_overhaul.pdf
 
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