Rear brake gets harder sometimes when riding

[Alcove]

When you pump it does it firm up? If so it's most likely air in the line

 

[urastus]

Hi! I got something by applying all tutorials at the same time xD

I tried another caliper and had the same results so:

I disconnected lever and caliper, cleaned everything, pushed pistons all the way in, reconnected, new pads, bleed, 8 hours of zip tie, bleed again... and some other things like bleeding while the caliper was out of the bike and at the bottom of the bike and bleeding with two sryinges

I have only made a 15 minutes ride but the brake was consistent all the time.

if the problem appears again I will start from scratch by replacing the cable, which I prefer not to do because I have to remove the battery lock mechanism, the motor cover, ...

Thanks all!

8hrs of zip ties then bleeding with syringes? The zip tie thing is for avoiding a proper bleed ie syringes. Zip tie then a top up burp as per the video should rule air out and give you hard levers. What were the levers like after the 8hr zip tie? You might have a leak where fluid is coming out, and air is getting in? How do you store the bike? eg vertically? Although if it was front wheel up that would work in favor for the rear brake...

 

[KuRi]

I mean that I was in a trial error process. I did one thing then tried and moved to the next one.

the bite point is moving, that is the problem I am having. I bleed the brake and then I have very tight and nice feeling and braking power. Then I start riding and the lever gets harder than original... I leave the bike for 3 hours and then it becomes softer than original. Eventually it returns to the nice point again.

I do not think I have a leak because I checked the cable and all the connections and never found any liquid... It looks more like the water in the circuit theory or just over bleeding the system.

Anyway I have noticed that the front brake lever also changes its bite point a little, but it is not barely noticeable. And the rear brake after all the bleedings and cleaning is moving just a +-10% and I think I can live with it as long as it is braking nice and firm which it does.

sometime in the future I will change the whole braking system and will let you know how it goes.

I need the bike and cant spend more time on this. After summer I will try replacing the hose.

thanks for your help.

 

[Rotwilder]

I’m no expert but had a similar problem with my front brake. It turned out to be one piston sticking slightly due to a contaminated O ring. It eventually stuck on so the wheel wouldn‘t turn! I had to remove the caliper and pads to get home. Then I used proper brake cleaner spray and levered the pistons backward and forward and kept cleaning the whole area. Now the pistons work perfectly. After braking they both retract slightly which wasn’t happening before. The original problem was hard inefficient braking at the front, which seemed to get better (softer)the more I used the brake. Hope this helps.

 

[HORSPWR]

I mean that I was in a trial error process. I did one thing then tried and moved to the next one.

the bite point is moving, that is the problem I am having. I bleed the brake and then I have very tight and nice feeling and braking power. Then I start riding and the lever gets harder than original... I leave the bike for 3 hours and then it becomes softer than original. Eventually it returns to the nice point again.

I do not think I have a leak because I checked the cable and all the connections and never found any liquid... It looks more like the water in the circuit theory or just over bleeding the system.

Anyway I have noticed that the front brake lever also changes its bite point a little, but it is not barely noticeable. And the rear brake after all the bleedings and cleaning is moving just a +-10% and I think I can live with it as long as it is braking nice and firm which it does.

sometime in the future I will change the whole braking system and will let you know how it goes.

I need the bike and cant spend more time on this. After summer I will try replacing the hose.

thanks for your help.

Have you used the correct fluid, mineral oil?

 

[KuRi]

Yes, the original pink shimano mineral oil

 

[KuRi]

Ok... so... what was the problem? The MINERAL OIL... After trying everything I ended with new lever, new inserts and olives and new caliper... problem still persisted...

I bought a new shimano mineral oil and problem solved. I think the oil was degraded because high temperatures because this is the first time I see this problem and it has been reall really hot here (>45ºC), and I store the oil in my garage, not ventilated and exposed directly to sun.

Thanks all!