my bike is a daily ride. 07 FLHTC. after 80k with no brake problems other than pads i went out to get on it for the ride home from work and no rear brakes. pedal went all the way down. now i run an automotive repair shop so this aint rocket science to . caliper, hose and master right?? pads are ok. no leaks at any of the three pieces. appears to be the master bypassing. so i replace the master, bleed it off. bleed the system and all is right again.

Until 5 days later. same thing. go to go home and no rear brakes. neither time was there a warning sign. no pedal fade. nothing. im going to re bleed but i have no confidence that ive solved the problem. any input anyone??

 

Had same issue with front a while back. Turns out the pistons had a bunch of built up dust and wouldnt "push" out. Pulled caliper cleaned pistons, made sure they moved in and out of the housing and walla all is good.

 

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I would rebuild the caliper... nothing like a freshened up caliper...seals are probly shot.

 

Did you have the original fluid in it when the problem started or have you been replacing it as per manual?

 

I haven't had this problem yet, but nice to know of the possible solutions, as I'm sure I'll have this problem in the future. Had a problem with my front brakes awhile back, and did almosot everything to fix the problem only to find that during the previous front tire change, the shop bent one of my rotors. After doing all of the fixes stated here, and not having any change; a shop discovered the problem, changed one front rotor and problem fixed. I now always remove my rotor when I take a wheel in for a tire change.

 

It sounds like the problem is in the caliper...since you replaced the master cylinder, and can't see any external leaking. Presume you evacuated all fluid, and replaced it with the mc replacement...so unlikely to be related to the fluid. One other possibility is...the replacement mc you used is faulty. Not likely, but stranger stuff has happened.

Alan

 

You are right to be scratching your head, it is a weird one...

No external leaks - presume you have triple checked that the fluid level is still as you left it after replacing MC?

Pistons jamming in the caliper would still have you building up pressure so the pedal wouldn't go down and it would "feel" like you had brakes apart from the fact that pads would not get to the disk and therefore no brakes.

What if....

Pistons are not retracting correctly but pedal does as it is sprung loaded. Something needs to fill the void so you will start to suck air. It may take some time, but after each cycle of the brakes you would get a bit of air until ultimately you experience the failure you did???

Possibly exarcebated by the option of you parking te bike up with the fluid relatively hot then cooling down....changing the air pressure in the lines.

Total speculation - just working from first principles of brakes and hydraulics.

Like you said though, really peculiar.

Why not try bleeding them again and see if you get a whole lot of air out again?

 

yeah think i will try and bleed again. what puzzles me is how they work normal and then bang they r just not there. that and the fact that the failure occurs after the bike has been parked and not while its in motion. master was a new MOCO replacement so im sure its ok.

whats the subscribe comment about?

 

I had the same thing happen on a car i owned.The master cylinder went bad.I replaced it and bled the brake system. 2 days later the brake pedal went to the floor. I would pump the pedal really fast and get about 1/4 pedal.No leaks where found so I took the car to my mechanic.Turns out there was air trapped in the abs system and there was a special way it had to be bled.I'm not sure what my mechanic did because he was busy and didn't have time to show me. I'm still wondering if the master cylinder was actually bad or if it was just air in the system.