Front brake losing power

Around 2 weeks ago I was parking her with the center stand in a recently concrete paved area of the backyard when the floor cracked and there she went falling on her right side.

Because I had a cover and the givi crash bars nothing happened visually, I put her in a safe place and went on a business trip for one week.

When arrived, in the first ride, I noticed after some time the front brake lever being stiffer and stiffer as brakes were heating and power going drastically down.
At home removed the cap from the oil brake in the handlebar and pumped gently the brake while knocking on the oil hose. Did not see air coming out, went for another quick test ride and it remains the same.

Can it be air in the system?
Is there a simple & efficient way to remove it?

Thanks in advance for the thoughts.

Air in the system will make the lever feel softer and ineffective. What you are describing sounds like the opposite of that. Maybe the lever hit the ground and bent the master cylinder piston, causing it to not retract fully. This would prevent the pressure from evacuating back into the reservoir when the lever is released.

Maybe if the caliper hit the ground hard, it could have bent a bolt or pin, causing the pads to not retract from the rotor when the brake pressure is released.

Normally, you should be able to manually push the caliper off the rotor. Push the caliper against the rotor with your hands. You might not be able to feel anything move, but you can at least get a few thousandths of distance between the rotor and inboard pad. If you can move the caliper as described, it is probably not seized and this might indicate a lever or master cylinder problem. If you cannot move the caliper off of the rotor, maybe the problem is in the caliper or hardware.

Does the lever vibrate or rattle when applied? That might indicate a bent rotor.

Thanks for your thoughts, now I start to be worried...

It works normally until it heats after some moderate braking. and there is no vibration, just the feeling of the rotor sliding through the pads with no bite power and the lever with less and less travel.

There is no sign of anything was hitted when she fell.

Is the disc getting discoloured ( blue) ? If so then there must be some distortion of the caliper.

I ride offroad and falls are part of that scenario from time to time. On occasion after picking the bike up I have found that either brake could be a bit mushy, but it would revert to normal after some vigorous pumping.

I suggest taking off the caliper, cleaning the pistons, and then pushing them fully back into the caliper. If some air got into the system when the bike fell over, that action alone might push it back up into the reservoir. Then put everything back in place and slowly pump the lever until you feel resistance. When you are satisfied that the brake is gripping the disc appropriately then try the bike out at low speeds until you are satisfied with performance. If you are not happy doing any of this then bring it to the dealer.

Thanks, it's a good idea.

I did it already but did not try it yet due to bad weather.

The feeling on the lever is like going full travel when it is cool, and then being stiffer as the ride goes on after some braking.

My thought is that it might be air working as a pillow at low temp, and as it increases temp will expand and increase the pressure in the system maintaining the same pillow effect but much more, preventing the fluid to pressurize the tubing and caliper properly.

Because this never happened to me in the past I am not sure how to deal with it.

When you opened the reservoir cap, what was the brake fluid level? I would expect it to be quite low in your case, which would prove the stuck master cylinder theory.

icing777 said:

When you opened the reservoir cap, what was the brake fluid level? I would expect it to be quite low in your case, which would prove the stuck master cylinder theory.

Click to expand...

I'm trying to understand your reasoning here. Can you elaborate on the low fluid level/stuck cylinder theory?

670cc said:

I'm trying to understand your reasoning here. Can you elaborate on the low fluid level/stuck cylinder theory?

Click to expand...

I was just thinking that if the brake fluid was not returning, then it is still sitting down low, thus lowering the level in the reservoir. Am I wrong?

icing777 said:

I was just thinking that if the brake fluid was not returning, then it is still sitting down low, thus lowering the level in the reservoir. Am I wrong?

Click to expand...

Level in reservoir is ok, took it for a run after taking caliper and manually retreat the pistons, and braking was normal for around 60 miles.

Then, close to home pushed it a little more and did some heavy braking from around 100 mph to 20 mph when exiting highway. On that time lack of power and stiff lever returned.

I am thinking to bleed the system, but will do it only in a couple weeks from now since I will be out for work.

I don't know is it is relevant, and I don't remember how it was before, but when I press the lever cold and stopped, it goes the full travel with little resistance. Does yours do the same?

Soarezito said:

when I press the lever cold and stopped, it goes the full travel with little resistance. Does yours do the same?

Click to expand...

That sounds like the pistons are being pushed back into the caliper. Your first few applications of the lever are being used to re-extend the pistons to meet the rotor. Once they meet the rotor, then the lever will start applying pressure for braking like normal. About the only thing I can think of that would cause this is a bent rotor, which could be caused be the bike falling. I would imagine you would also feel some vibration or pulsation in the lever while applying the brakes, if this was truly the case.

The symptoms are not completely indicative of air in the system, but bleeding the brakes is easy and relatively simple, and it can't hurt anything, so it's certainly worth a shot.

At any rate, this is an odd problem.

icing777 said:

I was just thinking that if the brake fluid was not returning, then it is still sitting down low, thus lowering the level in the reservoir. Am I wrong?

Click to expand...

Oh. Well, it's a closed system. The volume of the cylinder in the caliper is what it is. The only way more fluid would fit there is if the pads wore down more, otherwise no more fluid can be down below. So if it's not down below it has to be in the reservoir. If it's neither place, then it leaked out, which would be a whole 'nother problem.

670cc said:

Oh. Well, it's a closed system. The volume of the cylinder in the caliper is what it is. The only way more fluid would fit there is if the pads wore down more, otherwise no more fluid can be down below. So if it's not down below it has to be in the reservoir. If it's neither place, then it leaked out, which would be a whole 'nother problem.

Click to expand...

I see... Thanks for the clarification!

670cc said:

Oh. Well, it's a closed system. The volume of the cylinder in the caliper is what it is. The only way more fluid would fit there is if the pads wore down more, otherwise no more fluid can be down below. So if it's not down below it has to be in the reservoir. If it's neither place, then it leaked out, which would be a whole 'nother problem.

Click to expand...

Exactly, that is why I am thinking on the air like the most probable cause.

Again, no leaks, no vibration when braking, no sign of mechanical impact when she fall.

Also if there was glazed pads the feeling in the lever (stiffening) would not change I believe.

This is a typical case that sometimes people start from the opposite end of the equation when it comes to problem solving...

Tried lots of things and next step would be to bleed the system, but before that was passing close by the dealer and pulled over to speak with the mechanic.

Explained the symptoms and his comment was "that's odd..." then got to the bike, gave some pumps in the lever and asked me "did you noticed that your reach adjuster knob is touching the accelerator cable protection??" I was really emabarassed and told him. "No I did not, and you solvd my problem"

When she fel, and beacuse it had the cover, no scratching was visible in the lever but it rotated upwards a few milimeters. And because it was touching very little I did not realized it. When system heated, I needed more travel on the lever but it was hitting the cable protection.

Problem solved, I am embarassed but happy

By the way the lever is the puig model (black color with golden reach adjuster knob) and I love it.

Thanks for your thoughts but I was assuming a wrong thing from the begining, there was some mechanical impact after all.