Front Brakes Question

[JordansCycles]

The front brakes are double disc on my bike. When I go out to ride they lock up.. I let a little fluid out and let it suck in a little air and it was better for about 5 minutes then they locked up again. Not sure what to do, is a new master cylinder in order? If I need to rebuild the master cylinder or replace it I plan on buying a brand new whole master cylinder set up for a honda cbr because they are selling for $50.

[hampshirehog]

Sounds like the system needs stripping down and cleaning very thorougly ie complete strip and complete clean. Could be crud in your lines blocking the tiny hole in the MC or too much gunge down on the pistons. If you haven't already done so I'd advise replacing the lines with braided.

[Steve]

It sounds like you only need to clean the master cylinder. There is a very small hole that is a return port that clogs easily if the fluid is not changed regularly. When that port closes, pressure builds up due to the heat generated by the pads dragging on the disk. The fluid is normally allowed to vent back into the reservoir, but the clogged port forces it to squeeze on the pads, applying the brakes.

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[JordansCycles]

If I was to clear that port do you think just flushing all the fluid would suffice? as supposed to a complete tear down

It sounds like you only need to clean the master cylinder. There is a very small hole that is a return port that clogs easily if the fluid is not changed regularly. When that port closes, pressure builds up due to the heat generated by the pads dragging on the disk. The fluid is normally allowed to vent back into the reservoir, but the clogged port forces it to squeeze on the pads, applying the brakes.

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[SqDancerLynn1]

Flushing would be better than nothing, You should remove the MC and clean the return port first

[Steve]

If I was to clear that port do you think just flushing all the fluid would suffice? as supposed to a complete tear down

It is necessary to take the master cylinder off the bike and take it apart to gain access to that port.
In the process, you will end up changing all the fluid, anyway.

Simply changing the fluid will NOT clear the port.

You will need to remove the piston so you can examine the bore and you will need to remove the inlet fitting (the one on the side that receives the fluid from the reservoir) to see the tiny little hole. When you remove that inlet fitting you will see two holes. The smaller one that is closer to the top is the one that is clogged. Use a single strand of copper wire from a 16 buage or 18 gauge wire to poke through the hole, then spray some brake cleaner through there to make sure. When you have the wire strand through the hole, you should be able to see it through the end of the cylinder.

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[JordansCycles]

thanks for the replies I will do this likely tomorrow and report the results!!

[Nessism]

There was a member here a while back that crashed out because the front brake locked up on his bike. Brakes are nothing to mess around with. I suggest a full system tear down, clean out, and replacing the old sacked out rubber brake line if your bike still has them. Pumping clean fluid though doesn't get all the crud out of the system; it's like rinsing your dirty/oily hands with water but not using any soap.

[TooManyToys]

+1 .

[JordansCycles]

i cant seem to find the return port.. I opened the master cylinder and in the bore I just see three holes on the side coming down from the resoviour. am I supposed to take the resoviour off? I blew 90 lbs of compressed air through each hole then cleared the bore with it and I blew the same threw the calipers after opening each end of them...

Update: I reassembled the whole system and tried it out, it bled for 3 pumps then completely stopped bleeding or doing anything. The lever is dead. The master cylinder is leaking from the main seal and the resoviour. The pistons on the calipers were stuck in too far which caused the pads to be shoved against the rotors so I pushed them back.. hopefully that'll be enough. The plan now is to buy a working cheap master cylinder I don't want the new one it's some junk aftermarket brand.