4 replies to this topic

[coxy_gg]

hi all

i have a gas gas 300 racing 2010 model. the problem is that last week i had took the back wheel out of the bike to clean the dog bones, put the wheel back in and had no brake at all$! but the weekend before when i had been riding the brake worked perfect all day. i looked around the seals, banjo bolts etc etc to see if their was any leaks and also checked and their had been no fluid lost and have found none so thought it could of been the seals in the master cylinder that had gone. well ive replaced the seals with a new ajp cylinder repair kit and have rebled the back brake up. for about 4 or 5 pumps of the pedal i had a nice solid back brake although there was alot of travel (thought this could of been due to it been at the minimum adjustment level), after the 4 to 5 pumps the back brake suddenly dissapeared and stopped working again just like it had done before.

Does anybody know or have any idea on what could be causing this or a solution to my problem?

Many thanks
Coxy

[JSE]

coxy_gg, on 10 February 2011 - 08:00 PM, said:

hi all

i have a gas gas 300 racing 2010 model. the problem is that last week i had took the back wheel out of the bike to clean the dog bones, put the wheel back in and had no brake at all$! but the weekend before when i had been riding the brake worked perfect all day. i looked around the seals, banjo bolts etc etc to see if their was any leaks and also checked and their had been no fluid lost and have found none so thought it could of been the seals in the master cylinder that had gone. well ive replaced the seals with a new ajp cylinder repair kit and have rebled the back brake up. for about 4 or 5 pumps of the pedal i had a nice solid back brake although there was alot of travel (thought this could of been due to it been at the minimum adjustment level), after the 4 to 5 pumps the back brake suddenly dissapeared and stopped working again just like it had done before.

Does anybody know or have any idea on what could be causing this or a solution to my problem?

Many thanks
Coxy

Coxy,
If you disconnect the lever and use a Phillips screwdriver to pump the M/C, do you get any pressure?

Jon

[coxy_gg]

hi jon

when i use the brake lever there is no pressure what so ever and i have also tried your method with the screwdriver and there is no pressure at all. if i bled the brake up again we would get a decent brake for the first four or five presses of the pedal and then it just suddenly disappears and there is nothing again.

any help would be greatly appreciated.

Cheers!

[JSE]

coxy_gg, on 11 February 2011 - 09:20 PM, said:

hi jon

when i use the brake lever there is no pressure what so ever and i have also tried your method with the screwdriver and there is no pressure at all. if i bled the brake up again we would get a decent brake for the first four or five presses of the pedal and then it just suddenly disappears and there is nothing again.

any help would be greatly appreciated.
Cheers!

Provided you got all the air out of the line (and that usually is a bear of a job, but you say you get pressure at first) I'm wondering if maybe there's something in the master cylinder bore, perhaps a manufacturing defect, that is affecting the seal of the piston. I'd inspect the bore for any problems next to eliminate that as a possible cause.

Jon

Edited by JSE, 12 February 2011 - 01:00 AM.

[coxy_gg]

hi jon

thanks for your help, we have bled the brake again exactly the same as the time before and upto now it has all been fine, will find out for sure tomorrow when i ride it. im guessing i must of had some air in the system which when the brake pedal has been pumped has moved to a position where it can be squashed or something as all i did was re bleed the brake and its came good and stayed good for atleast a day now.

cheers