bouncing front brake

[byron]

recently fitted a new ScootRS disc brake to a mate's scooter.
replaced the [rather dire] supplied hose with quality Goodridge hose & fittings.
MB uprated fork springs, spent some time getting everything in line, MB links, replaced steering bearings
on the bench all was good.
it seemed to fit better than others I have fitted, there was no movement of the caliper bracket on braking

but on the road, although the front brake does work well, it feels as if it is going on & off, resulting in the front end going up and down, and generally not feeling too confidence inspiring. this on/off/on/off sensation can be felt at the lever.

the fork bearings are fine, taken the hub apart and put it back together, still no joy.
warped disc maybe...?
pistons not behaving as they should... ?
it feels more like the brake itself, than anything to do with the forks or suspension...

it's frustrating, I've fitted a few hydraulic front brakes before and my mate was really looking forward to having something to actually stop his scooter..

any tips or experiences shared appreciated
thanks

[paulmgreen]

check the disc carefully - you may find it is warped...

[martinr]

what type of master cylinder are you useing will the lever pull in all the way if you keep constant pressure on it

[cezeta]

mrs cezetas scootrs vespa brake is the same. its not warped but i suspect that it either has an area which is a bit rougher than the rest or that its thickness is not consistent.

also look for a small crack or burs in the drilling.

once you've found out whats wrong.....let me know what i need to do

[byron]

it's the master cylinder that came with the kit, the lever won't go back to the bar, only goes as far as is acceptable, the brake feels fine on the bench.

after talking with Angry Bloke tonight, who is has been fitting the same to his bike, I am going to check the relationship between the disc and the pad faces, I suspect they may not be in line consistently, and some shimming may be required...
I will also look at the disc, good point about burred holes, roughly checking in situ with a steel rule it seemed ok, certainly no worse than the one on my bike, which works fine, and has done for 000s of miles

[sean brady scooters]

sorry to back track on this ...and sorry for asking maybe a stupid question.....but do you have shockers/dampers fitted..?

[byron]

yeah, there are dampers fitted, standard types, I did wonder if they are not doing what they're supposed to do to, I will check they're damping the right way. but it does seem more brake, than suspension related at this point...

[byron]

I've loosened the caliper on the bracket, spinning the wheel, it always catches and lifts the caliper up at the same point, so as if the disc is in fact not entirely true...

[byron]

check the disc carefully - you may find it is warped...

is the right answer....
whipped the disc off my bike, fitted it to my mates, changing nothing else, it worked as it should have all along...

the kit was bought with cash from a stall at wicksteed, no idea who it was...
so where can he get a new disc from ?? MB ?
preferably one that is up to the job...
it was a bit disconcerting to note that his new disc was about 0.4mm thinner than my disc, that has had over 9000 miles of use, with the inevitable hard braking occurrences.... that's shite really....

[dapper]

If its not too warped, can't you get it sorted out at a machine shop?