Yamaha R6 Forum: YZF-R6 Forums banner
1 - 12 of 12 Posts

·
Registered
Joined
·
28 Posts
Discussion Starter · #1 ·
Hello,

I rebuild front brake master cylinder and also both calipers with new seals.

When Im trying to fill oil back and bleed the system, air is getting out and I can see little bit of oil going out in rubber tube but pistons doesn't even try to move to squeeze brake pad. No pressure

I spend pumping over 2h both and I have no pressure to pistons but oil does go through.

There is no leaks.
 

·
Registered
Joined
·
3,779 Posts
As long as there is any significant amount of fluid escaping, it won't be able to build stable pressure. If you can't easily move those pistons then they are seized. Double check to make sure that you're doing the fill and bleed procedure properly.
 

·
Registered
Joined
·
28 Posts
Discussion Starter · #3 ·
I got it fixed, air in master cylinder. After rebuilding master cylinder and calipers. Anyway I have another question.

This is my first bike so I have no comparison other than below.

Brakes in Yamaha r6 2003 compared to Kawasaki 636 2005 are twice less powerful (only bike I compared to).

I have rebuilded front brake calipers but still they are not very powerful.

Maybe R6 2003 they are made like this and can't be stronger ?

I never changed pads in this bike since I owned because they not worn out (they seem old tho).

I also believe that my lines are braided.

Please see pictures.
Automotive tire Bumper Wood Gas Glove

Automotive lighting Bumper Gas Automotive wheel system Fashion accessory

Fluid Finger Material property Drink Nail
 

·
YZFR6... ooodles of HP
Joined
·
1,522 Posts
Pad material and rotor surface condition effect on the bite of the brakes are only 2nd to a new properly flushed/bled system. Sounds like you have could have brake drag ie excessive heat or the pads need examination. Assuming you have no leaks. Did you pump numerous times then zip tie the lever tight and return a few hours later to examine every threaded point in the system for leaks if the lever dropped? EBC HH copper increase bite and reduced the buildup on the rotor for me.
 

·
Registered
Joined
·
3,779 Posts
I chirped the front tire braking so hard last week. I've never been dumb enough to do it but I'm sure I could easily lock it up if I really grabbed it. Try OEM semi-metallic pads and rotors.
 

·
YZFR6... ooodles of HP
Joined
·
1,522 Posts
Drum brakes from the 80s do nothing when you clamp them above 50mph.. then at 35-40mph they will lock her up. Any dual rotor front non abs clearly hasenough mustard to lock. Now with HH pads and a new pilot road 5 at 65mph my r6 on very hot clean asphalt can handle an amazing amount of braking before the abs will even pulse. And that is probably half of what the brakes can put out. In the rain obviously I barely get my index on the lever and trip the abs.
 

·
Registered
Joined
·
28 Posts
Discussion Starter · #7 ·
If I push fully on front brake I can't lock them up. I never tried applying zip tie to the fully squeezed lever to see if it dropped after few hours but I didint notice any leaks.

I'll try that before buying new expensive rotors. I never cleaned them too.

These pads I have there are made from organic but would that be that big difference of braking compared to ebc hh sintered pads ?

I rebuilded caliper all pistons are moving don't know where to start next.

I just been recently on MOT test (UK certificate for 1 year).

How on earth these brakes passed, they can't lock even during slow ride.
 

·
Registered
Joined
·
3,779 Posts
Use Velcro instead of zip-tie. Don't want to hold an extreme amount of pressure to it for hours for fear of the silicon seals developing a "memory" of that stretched state. You just want pressure is all.

Organic pads are decent for dry weather but bad for cold and/or wet weather. Avoid kevlar pads... they should be outright illegal on a motorcycle.
 

·
YZFR6... ooodles of HP
Joined
·
1,522 Posts
Well to clarify you pump the lever a bunch of times. Apply finger pressure until it stops. Zip tie so it holds. The piston seals and master cup seals are designed to hold the pressure. If it can't hold a seal for an hour or two, you will be able to squeeze the lever tighter then the zip tie is holding. Then you have a leak or cup failure. It is rather common place to use line lock valves for racing/stunt cars and for an aftermarket parking brake on rear disc brake vehicle conversions with no mechanical e brake caliper or gm style drum in rotor systems. They work by applying brake line pressure then closing the valve to hold static the operating pressure (500-900 psi typically). The caliper and master cylinder seals are designed so brake pressure increases the contact with their bore enhancing the seal. Hence why the cup shape goes a specific direction in the master. Fluid expands the hollow cup lip.
 

·
Registered
Joined
·
28 Posts
Discussion Starter · #10 ·
Hi guys,

I still have a problem with the front brake. I replaced the master cylinder, rebuild both calipers, and brake lines are braided. The system is fully bleed from the master cylinder down to each caliper. Can't see any air bubbles at all anywhere in the system.

The brake still feels spongy and braking power is very low. Running out of ideas. Only thing I haven't done is brake pad change but they have plenty material on it.
 

·
Registered
Joined
·
3,779 Posts
I chirped the front tire braking so hard last week. I've never been dumb enough to do it but I'm sure I could easily lock it up if I really grabbed it. Try OEM semi-metallic pads and rotors.
I agree with that guy ^. (as well as the others) 😏

Keep in mind that it can take a couple of tanks of fuel to embed the brake pads meaning, your braking friction will be reduced.

On my car, went from OEM to aftermarket organic and the drastic difference with initial bite gave me the impression of "sponginess". I am fine with it since I'd rather replace pads over rotors. The harder pads merely wear out your rotors (way) faster.
 

·
Registered
Joined
·
28 Posts
Discussion Starter · #12 · (Edited)
I agree with that guy ^. (as well as the others) 😏

Keep in mind that it can take a couple of tanks of fuel to embed the brake pads meaning, your braking friction will be reduced.

On my car, went from OEM to aftermarket organic and the drastic difference with initial bite gave me the impression of "sponginess". I am fine with it since I'd rather replace pads over rotors. The harder pads merely wear out your rotors (way) faster.
Hello mate,

I bled the system once again today and still spongy lever and low braking power. After bleeding every banjo bolt and both calipers I disconnected calipers to see what is happening during lever squeeze.

Pistons are moving back and forth slowly till both are fully extended. Very strange. I don't have experience but it doesn't seem right. I made a video.

I also performed a zip tie test on the brake lever and the pressure was holding the same as I left it overnight,
The second thing is my brake fluid color. I rebuilt the master cylinder with a full brake fluid change and after 1-2 months brake fluid color seems much darker than the new one but maybe that's normal?

Please see the video here: Yamaha R6 - Google Drive

Before I change rotors or pads I need to make sure that pistons pushing full power but I think that's due spongy lever not creating enough pressure that's why braking power is low.
 
1 - 12 of 12 Posts
Top