I have a 2001 F4I which I bought roughly a year ago. The bike was in pretty rough shape, it was wrecked by the previous owner. Its only the second bike I've ever owned, and I'm still figuring out troubleshooting/maintenance. I have it pretty much restored, with the exception of the front brakes.

So when I bought it, the front brakes were extremely spongy. It had stopping power, but definitely didn't feel right. So I put new brake fluid in and bled the system, which did not fix the issue. The only thing that changed is that now, the front brakes stick and hold the rotor tight after being engaged. When riding, they'll slow the bike to a complete stop without me pulling in the lever at all.

To try and solve it, I also rebuilt the caliper which was sticking, on the left side. In addition, I replaced the master cylinder. The lever feels pretty good, but the brakes still stick.

The strange thing is that if I push the brake lever out (forward, away from me), it releases the pads and the bike will roll freely. The last thing I can think to do is replace the lines, which I can't see being the issue.

Like I said I'm still pretty new so it could be something extremely obvious that I'm missing. It would seem that the issue is in the master cylinder?

Any and all help would be greatly appreciated!

 

The "push the lever forward" sounds all wrong.
If it was mine I would start the whole process of refurbishing the brakes again. Ignore what you presume as already done by you or your going to go round in circles . Spongyness can be caused by a few things and including as you doubt, brake lines, as they swell under pressure when they deteriorate so as you suggested, replace it. It's another tick in the box on sorting the issue .Seals and fluids are relatively cheap compared to what a poor brake could cause.
Check the pins ( sliders ) that hold your pads in position. These allow the pads to not only bind the disc squarely but return as you release pressure. Clean caliper pistons and even take a look at your brake lever, check it all. It's a fairly straight forward circuit and with the exception of a faulty caliper you'll be able to sort this
Finally a good bleed and your done.

 

Wild guess...you, yourself, mentioned that the bike was in an accident and that the brake lever needs to be pushed forward so could stiction / binding be a factor because the brake lever took a hit?
If the brake lever doesn't retract freely, that could definitely cause the binding.

Wild guess..somewhat.

 

Thank you for the reply,
I think the lines are the next thing I'll be replacing. I did in fact replace the pins. In addition, when I replaced all the seals in the caliper I did clean the pistons themselves.
Could deteriorating brake lines cause pressure to be held on the pads? I'm trying to determine if the spongyness and sticking are two separate issues or not?

 

Hello, thank you for the reply,
Not too wild of a guess I don't think. I'm really not sure where the problem originates from, so I'll throw another lever on the bike to see if that makes any difference at all.

 

Yes. When they collapse, the can act like a one way valve.

Braided lines are the way to go, at least for the front.

 

+1 for braided lines. Once you've had them, you'll always want them.
An opportunity arose for me to test my new braided brakes on the motorway a few years back and still remember it.
I had bedded in a set of sintered pads a while back and flew into a large gap with nothing in front or behind me and the thought just came to me.....how quickly can I stop this thing at these speeds....the noise was awesome as the pads gripped hard and long, no fade, and nice and consistent with a serious reduction in mph . Yeah, good . Well worth going to braided if changing out.

 

f4i_guy, when you rebuilt the caliper/calipers, did you polish the pistons and the piston bore? Did you do both or just the one? Maybe the other one is the problem. My F2 brakes were dragging so I removed them from the bike, left lines connected, washed and scrubbed them with hot soapy water and a toothbrush. Rinsed and dried. One at a time of course, I put different sized spacer inbetween the pads and squeezed the lever until the pistons were exposed, then lubed the pistons with 1 drop of brake fluid. If you go to far the pistons will come out completely making a mess, thats why you do one at a time. Leave the other on mounted on the bike in the normal fashion. When done with the first one, do the other one. The F2 has solid mounted rotors and floating calipers, where as the f4i is the opposite I believe, So I had to also make sure my calipers were floating on the pins like they supposed to. Maybe your floating rotors arent floating as much as they supposed to. You should be able to pinch the "buttons" between your index finger and thumb and turn them, if they dont there is probably brake dust build up in there keeping them from doing that. There is utube video that shows how to clean and lube those buttons. I did it to my 08 CBR 1000RR just as a preventive thingy.

 

Thank you all for the advice. Upon closer inspection, I realized that the brake lever which the previous owner installed was not correct. As a result, the "button" on the master cylinder was always pressed in a bit, which held pressure on the pistons. With an OEM lever in place, the problem is resolved.
I still think I may move to braided lines just for better performance, especially with all of the recommendations I've heard.