Front brake - not quite right

Howdy

My front brake over the last few weeks has began to fell different. From high speed slowing down all works fine. At slower speeds 20-30 when slowing there is a distinct one and feel.

My thoughts are could the disc be warped? how would i check this?

new fluid perhaps? had some put in 3000 miles ago with new pads



Any thoughts would be appreciated.



Thanks

May possibly be a warped disc, either that or the piston seals are on their way out and need replacing. Check that the sliding pins are moving freely; if these have never been serviced the sliders may well be seized.

On mine I had a combination of the two; the piston got stuck and that in turn warped the disc; I had to take the caliper off and tie it up so I could ride home!

I had a similar problem with low speed braking feeling 'lumpy' especially just coming to a stop in the wet. High speed braking seemed fine.
I checked the disc by holding a pencil against the fork leg with the tip just touching the disc and span the wheel when clear of the ground. I noticed a minute gap about the width of a fag packet between the pencil and the disc around part of the circumference so I replaced it. It seemed to solve the problem.


Also I agree with teamster about greasing the sliders. Easily neglected and easily fixed.

UPDATE

Not been using the 500 much recently with the good weather so have started to look at the odd bits that need tinkering with. Update on the front brake problem. Removed caliper from disc to take a look. With the pads removed and the brake lever pulled in the top piston hardly moves at all. Put a block of wood in front of lower piston and squeeze hard the top piston does move. This I'm guessing could be the reason for my problem. From speed, plenty of front brake feels fine. Slower speeds less front brake equals only one piston doing the work therefore bike feeling on/off - lumpy.

Any thoughts?

With no resistance its quite possible for one piston to appear to move much more freely than the other. If you can push both pistons back in to the caliper with your fingers then they aren't sticking.


Your problem sounds exactly the same as mine before I replaced the disc. Hard braking is fine but as you roll up to a junction slowly it pulses. It seems to be very sensitive to a warped disc. Ensure your pins are well greased to avoid warping in future!

Hi,

good advice so far. Might be worth changing the pad pin as these can get worn and affect the movement of the sliders. Also, get some PJ1 brake cleaner and douse the caliper on the inside, clean up the crud on the pistons (move them in and out a little with the lever and a g clamp). When putting it all back together put copper grease on the back of the pads and on the pad pin/slider. It'll be smooth after this but if it still plays up, look at the disc itself as said. Btw you can put pj1 on the disc to get it clean too.

m1