2016 CBR1000RR with a serious brake problem. Help diagnose?

[mudduc]

I just road a 2016 CBR1000RR with a serious front brake issue.

Parked, you can pump up the brakes and get a good feeling grip and solid lever. Start moving just a few feet and try to brake again and the lever goes to the bar without any resistance at all. Pump a few times and the brakes are back with a solid feel. Roll another few feet and they are gone again but come back with a few pumps.

Brakes were bleed well. No air in lines anywhere.

I'm guessing master cylinder has a problem and would recommend to the owner to swap it out but I don't know enough about the inner workings to know what would cause the problem. Is there an internal one-way valve that is busted?

Anyone else have this issue and know the cause and resolution?

Thanks,
Kent

 

[Whooshka]

Probably the piston and bore in the master cylinder are kaput. They have rebuild kits for the mechanically inclined buts it easier just to swap out the whole unit and rebleed.

 

[mudduc]

Thanks Whooshka!
I just talked to an engineer friend who has rebuilt a lot of Spanish (trials bikes) master cylinders after having a similar problem. He says the cross-bore hole from the reservoir can eat up the piston seals and give the symptoms observed. With you that's two votes for problems with the master.

I'll see if the owner feels like doing a rebuild or just a master swap.

Later,
Kent

 

[Igofar]

Psssssst....hey buddy, have him buy a rebuild kit, get a pair of snap ring pliers, and replace the piston if your just throwing solutions at a problem, instead of finding the cause of the problem.
You say it was bled properly? how do you know? did a shop do it? If so, they probably used a vacuum pump, sounds like a few things could be wrong.
To save your buddy some $$$, try these things first:
Open up the master cylinder and see if someone inverted the deflector spoon (put it back in upside down) this will prevent fluid from returning and lock things up.
Pick up a childrens asperator (ear bulb) and suck/flush both the primary hole (under the spoon) and the return hole (next to the primary one) and see if either of these are clogged up.
Either one of these can cause your symptoms....
And lastly, because this will cost money (I do free/easy stuff first) replace the piston with a rebuild kit for about $20 bucks.
Your friend is right, the rubber seals flatten out and fail when not flushed often enough.
Hope this helps.
Let us know what you find.

 

[mello dude]

I just road a 2016 CBR1000RR with a serious front brake issue.

Parked, you can pump up the brakes and get a good feeling grip and solid lever. Start moving just a few feet and try to brake again and the lever goes to the bar without any resistance at all. Pump a few times and the brakes are back with a solid feel. Roll another few feet and they are gone again but come back with a few pumps.

Brakes were bleed well. No air in lines anywhere.

I'm guessing master cylinder has a problem and would recommend to the owner to swap it out but I don't know enough about the inner workings to know what would cause the problem. Is there an internal one-way valve that is busted?

Anyone else have this issue and know the cause and resolution?

Thanks,
Kent

I'm with the gang here, do a master cylinder rebuild, also add speedbleeders to the calipers. You'll get a better bleed job. - If you can do a reverse bleed also try that too.

 

[Whooshka]

Psssssst....hey buddy, have him buy a rebuild kit, get a pair of snap ring pliers, and replace the piston if your just throwing solutions at a problem, instead of finding the cause of the problem.
You say it was bled properly? how do you know? did a shop do it? If so, they probably used a vacuum pump, sounds like a few things could be wrong.
To save your buddy some $$$, try these things first:
Open up the master cylinder and see if someone inverted the deflector spoon (put it back in upside down) this will prevent fluid from returning and lock things up.
Pick up a childrens asperator (ear bulb) and suck/flush both the primary hole (under the spoon) and the return hole (next to the primary one) and see if either of these are clogged up.
Either one of these can cause your symptoms....
And lastly, because this will cost money (I do free/easy stuff first) replace the piston with a rebuild kit for about $20 bucks.
Your friend is right, the rubber seals flatten out and fail when not flushed often enough.
Hope this helps.
Let us know what you find.

While I agree with going the cheaper route first 2 things tell me to go the easier route in this case. #1 the owner doesn’t have enough knowledge to even diagnose the problem which leads to #2... the OP admits to not knowing about the internals of a MC so I wouldn’t trust doing the rebuild kit right. Not on a safety item like brakes. Swapping out the MC is basically 2 bolts on that bike.

 

[mudduc]

Man, I feel like such a noob. Of course it's a warped rotor!

I've never had the problem in the past and didn't jump on the rotor as an issue since I didn't feel any pulse when braking but once it was brought up here, it sparked as the obvious problem.
Went back to my friend's with a front-end stand and the rotor problem was easily obviously apparent.

Thanks for the help. I'll shuffle off in shame.

Later,
Kent Larson in Minnesota