Hi guys,

Today I changed the brake pads on the F4i, and ran into a problem. The rear brake now has very poor stopping power... and feels very spungy.

I didn't do anything with the brake fluid... I just took off the old pads, cleaned the surrounding area, pushed the cylinder back in... and installed the new pads.

I've tried pumping the brake lever over and over.. but it still doesn't have the power it should. Any idea's on what caused this, and how I can fix it before my track day on Wednesday? Any help is greatly appreciated!

 

Check the fluid level, most likely you need a flush and fresh brake fluid.. common practice to change brake fluid along with installing new pads.

 

Give the new pads a chance to mate with the old rotors. Once the two surfaces form to each other, the entire pad will touch the rotor surface and work better.

 

Or maybe you got some air in the brake line, i also think that you have to change the fluid and try...

 

Thanks for the quick responses everyone. I'm going to try bleeding the rear brake right now, and I'll post the result. Hopefully a good one result!

 

Did you pump the brake multiple times before riding it? If not, the pads needed time to shift back to their normal position after being pushed outwards.

Did you bed the pads at all? Going out and doing a few good hard brakes at various speeds after installing new brake pads is recommended practice for any vehicle (car or bike).

 

when i put EBC pads on the back, my whole rotor was flexing...bought a used rear caliper and everything with it to try it on that one and it did the same thing, so i am running OEM pads from the part i bought.

 

Yea you need to bed the pads if they are new, anywhere from 50-600 miles for rear if I'm not mistaken. Bleeding the brakes is never a bad thing either. Good luck and have fun at the track!

 

Sorry I didn't reply to the thread after I bled the brakes... I wasn't in a very good mood the last few days. Needless to say, bleeding the brakes didn't fix the problem. After I did it, the brake felt exactly the same... mushy. And yes, I tried riding the bike and breaking hard to try to wear the pads in, but it didn't help.

So I gave in and took the bike to my local shop for a diagnosis. They called me back today, and said they also tried bleeding the brakes and reinstalling the pads... and it didn't fix the problem. They said after further testing they found that the problem is the master cylinder. The parts and labor is fix it is only like $150, so it's not that big of a deal. I'm just curious how the master cylinder got messed up... because it worked fine before I changed the pads.

And because of all this, I missed my track day, and they don't give refunds! Note to self - don't fix things the night before a track day!

 

My guess is that when you pushed the pistons back into the rear caliper, there was some sediment or debris in the system, which got pushed back into the rear master cylinder and damaged the seals.

Keeping fresh fluid in the system will minimize the chances of that happening, But sometimes the system has to be completely disassembled, flushed, and the master cylinder and calipers need to be rebuilt.