Rear brake pedal problem.

[fzar]

I changed the pads on the rear yesterday, bled the brakes and now the pedal is going all the way to bottoming out with no resistance on the rotor. I cleaned, lubed what was needed, re-bled the brakes 3 times and it 's still the same. Maybe M/C problem? I think its a caliper dust seal problem! but I don't know. Just putting it out there. I had no problems riding 10 days ago, I'm getting fluid coming through when I bleed the line, but nothing on the rotor. resistance- wise. It's literally  bottoming out even if I pump it to get pressure.

Any help appreciated.

[stickshift]

Sounds like air still in the system. I'm not near my bike at the mo, but the master cylinder might be the highest point trapped air will rise) - try bleeding that in the normal way and cracking open the bolt (use a rag to collect the fluid).

[mossrider]

What Stick said, use the front banjo bolt to bleed it. 

If that doesn't work, take the rear caliper off and put something hard and the approx. thickness of the rotor between the pads. Elevate the caliper and try bleeding it again. 

If that doesn't work use a mighty vac to bleed it. (works every time)

If that doesn't work ur effed.  Seriously, be patient, check your work, keep the resivoir full and it'll be fine.

[shinyribs]

1 hour ago, fzar said:

I changed the pads on the rear yesterday, bled the brakes and now the pedal is going all the way to bottoming out with no resistance on the rotor. I cleaned, lubed what was needed, re-bled the brakes 3 times and it 's still the same. Maybe M/C problem? I think its a caliper dust seal problem! but I don't know. Just putting it out there. I had no problems riding 10 days ago, I'm getting fluid coming through when I bleed the line, but nothing on the rotor. resistance- wise. It's literally  bottoming out even if I pump it to get pressure.

Any help appreciated.

How many miles/ age is on the bike? This sounds like something I've run in to before, but never on a bike this new. So I'm not gonna prattle on unless it seem relevant. 

 

edit: May as well prattle...

Three time now ( once this past week) I've had a brake that wouldn't produce pressure for seemingly no reason. Either bleeding a system that was currently working, but suddenly stopped making pressure after flushing it ( sounds like yours ), or a master cylinder that I rebuilt that wouldn't make pressure with new seals installed. 

I think what happens is when you go to bleed a brake you end up moving the piston much further in it's bore vs what you normally do when riding, so the seals on the piston travel past an area they normally don't see. If there's any corrosion/pitting in that new area it can damage the seal. But I really hope our master cylinders wouldn't be prone to that much corrosion so soon! I ended up with your exact symptoms (different bike). The brake was working fine but suddenly won't produce pressure after a simple bleed job. You can pump straight brake fluid out of the bleeder with NO air bubbles present, but still no pressure. 

Twice I've rebuilt a master cylinder and had the same no pressure issue. Ended up having to hone to bore of the master in order for the the new seals to seal up and produce pressure. A buddy of mine gave me the advice to hone after I had a brake that just would not make pressure. Sounded crazy to me, but I trust his experience. Gave it a shot and it worked great.

This is what I use for a hone. A #2 pencil with a slit cut in it. I use 600 grit wet/dry paper lubricated with brake fluid. First time I did this the bore looked perfect to me before honing. After a quick pass with the hone it revealed TONS of low spots. Honed those spots out, refilled the system and it bled out instantly. 

Seems much more severe than it really is. It's an easy job. I'd hate to think your bike is acting up like this, though. Seems way too soon. 

 

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Edited January 26, 2020 by shinyribs

[fzar]

2015. 26,700 miles. I bled the brakes F/R  before this no problems. I installed SS brake lines and bled them again. No problems. Installed front EBC HH pads 2 weeks ago, no issue. went to installing the rear and ..... I noticed the caliper piston isn’t hitting the back of the pad flush. Thanks for the prattle addition  btw. 

[sorkyah]

Sounds like a piston sticking in the bore if it isn't hitting evenly

Might need to hone/scrape the Piston bore and reinsert it

[DewMan]

If the pedal is bottoming out the fluid has be either leaking out ( or past a seal back into the resevoir) or there's air in the line that is being compressed, as long as the break lines are not bulging. I don't see how his stated issue can be a piston issue if it's not leaking.

[cornerslider]

Maybe remove the pads again, and compress the piston back into the caliper all the way (with a c-clamp) . Try to feel if it goes back in smoothly, or if it's binding up? It sounds like a caliper problem rather than a master cylinder problem. I would think you would be able to pick-up a used caliper pretty cheap? Good luck-

[i28]

so when you hit the rear brake, does the caliper tilt sideways a little bit?

that was the issue I once had and it was because of the threads on the caliper. I replaced the caliper from ebay

[sorkyah]

21 hours ago, fzar said:

I noticed the caliper piston isn’t hitting the back of the pad flush. Thanks for the prattle addition  btw. 

 

7 hours ago, DewMan said:

If the pedal is bottoming out the fluid has be either leaking out ( or past a seal back into the resevoir) or there's air in the line that is being compressed, as long as the break lines are not bulging. I don't see how his stated issue can be a piston issue if it's not leaking.

If the Piston is hanging up it could have trapped air on one side causing the pedal to bottom without the piston moving

[fzar]

On 1/26/2020 at 2:42 PM, sorkyah said:

Sounds like a piston sticking in the bore if it isn't hitting evenly

Might need to hone/scrape the Piston bore and reinsert it

Done. Same issue.Bottoming out no feeling at the pedal.

[fzar]

Here’s a few pics. No resolution as of yet. I’m going to rebuild or replace the MC as the cups seem to be the problem from what I researched. Rebuilt caliper already. Below is a lighting issue I think, I’ll pull it tomorrow again and check.

[peteinpa]

Before you pushed the pistons in to make room for the new pads did you clean them?  They get road dirt and even corrosion on them that needs cleaned off so it is not shoved passed the seals.

I've owned many bikes, some with 80-100k miles and never rebuilt a caliper or MC.

This is VERY unusual for such low mileage and age.

 

Edited January 29, 2020 by peteinpa

[sorkyah]

if you hooked up the line and put fluid through the system with the piston out have fluid flow through the ports on the caliper? maybe theres a blockage causing air to be trapped inside the caliper itself?

or perhaps not a complete blockage

 

[fzar]

All Done. Back in working order.

17 hours ago, fzar said:

I’ll pull it tomorrow again and check.

Like I said ^^^ I tried one more time. Pushed the piston out halfway with the pedal,popped the reservoir cap and diaphragm, pushed it back flush and got some bubbles up through the reservoir. Re-bled the line and it worked. What a PITA, no idea precisely what shoved the needle in my favor this time, but I'll take it. 

[YZEtc]

Very good, and I appreciate you coming back to post what you did to make it right.

[fzar]

Here’s another picture from last night that may have helped!! It sure as hell didn't hurt anything. After my first attempt on Saturday I did this too as I do when I bleed the brakes F/R (No I don't hang 10 LBs from the front lever) Constant back and forth flushing/bleeding at the Master Cylinder and bleed valve along with the caliper rebuild and about a 1/4 gallon of brake fluid (totally over done it) worked. Yeah I don't feel terrible smart on this one as I've done this before with no problems. I had to call @mossrider and a friend whos a MC mechanic in NY to get the lowdown on the easiest plan of attack as I wanted to ride Sunday @50F+.( Both had some great tips and advice BTW) But I held back and just didn't want to chance riding without the rear brake, either way it still had to be done,and the possibility of you'll need it right when you don't have it over rode my sense of carving up some roads. That and I find it hard to walk away knowing it beat me. Thank You, to all that responded. Definitely got the brain working.

[fzar]

12 hours ago, peteinpa said:

Before you pushed the pistons in to make room for the new pads did you clean them?  They get road dirt and even corrosion on them that needs cleaned off so it is not shoved passed the seals.

Initially No. It went back in by hand, new pads on and that's where the trouble started. I rode up the rode and had no feel and I could hear rubbing. Pulled the new pads and I could see the piston was cocked ever so slightly.  I checked rear wheel alignment and it was spot on. Tried pushing the piston back in with a clamp and I wasn't comfortable with the amount of force I had to apply as it was a quick grip 1 hander clamp, so if it doesn't want to go this way! How about the other way? So I pushed the piston out via brake pedal (brake fluid mess) I cleaned everything and ran some sandpaper over the piston and caliper interior, shots for everyone (brake cleaner). I got the piston lined up and slightly inserted and gave a little rub of grease and it slid back all the way flush by hand.

[peteinpa]

Oh now I see, didn't get that from your previous posts. You shot a piston out and lost all fluid.

That changes everything. It's VERY hard to fill a new system and get pressure and all the bubbles out.

Bleeding fluid without ever getting air in is comparatively easy.