Rear Brake Master Cylinder parts

[txm123]

Hello, I’m trying to bleed the system and I can’t make it...It seams that one of the rubber seals that go in the internal piston rod is defective, really I don’t understand how does it work? I made a picture to show how does it look like. It’s very common in all the china motorcycles, especially in dirt bikes, I think maybe someone can tell me if I can buy new rubber seals or a new pump if this is the problem. I tried to pump 100 times and no pressure; I cleaned and disassembled the entire cylinder but no results. Thanks.

[txm123]

Well it seems that nobody has been through this kind of issue yet....
today I tested the master cylynder and taking out the hose if I put a screw in the slot of the hose,the pressure of the pump starts to increase and it keeps there.So I must suppose that the pump is fine now.But when I attach the hose its really impossible to bleed the system.I guess I should try to change the hose and try to see what happens.

[david3921]

What happens to the fluid when you try to bleed? Is there any fluid that squirts or leaks out?

[txm123]

No,I mean thres no sound ,or bubbles coming out of the hose or caliper,I can see a very little movement at the pistons in the caliper,and its a strange movement because it moves 2mm lets say forward and after y realese the pedal it goes to the original position!!!

Maybe all the system is right and I´m not bleeding it correctly...

what do you think¿?

P.S.: one strange thing is that I can´t get any pressure,I mean could it be so much air in the caliper and hose so that after 100 pumps I can´t get pressure?

[CrazyCarl]

The caliper is supposed to return to a resting position after you squeeze... if not, then your wheel would always be locked!

Air can compress very much so if you have air in the line/system, you can pump 1,000,000 times and it will still not build pressure.

Are you using the bleed nipple on the caliper to bleed the brakes? If not, then you will never get the air out. You must use the bleed nipple on the caliper.

Bleed nipple will look like this:



You need to attach a clear hose to the top of the nipple and something to catch the fluid that comes out. Then:

1) PUMP the lever to build pressure and HOLD the lever close to the bar to keep pressure. (Do NOT pull the lever all the way to the bar)

2) LOOSEN the bleed nipple for only a couple seconds. DO NOT remove the nipple... only loosen it a little (maybe 1/4 turn) until some fluid comes out. When fluid comes out, you will feel pressure release on the brake lever.

3) CLOSE the bleed nipple.

4) RELEASE the brake lever and pump again until you build pressure. This will put more fluid in the line.

5) REPEAT steps 1-4 until it's firm and you see no air bubbles coming out of the bleed nipple.

Other notes...

1) Do not pump and bleed so much that you loose all the fluid in your tank! If you do, you will only pump air into the line! Be sure the fluid is filled to a good level before you pump again to build pressure!

2) Sometimes air can get stuck in the joint between the hand pump (master cylinder) and the brake line. To get this out, pump to build pressure and SLOWLY loosen the brake line bolt. Be careful because fluid may squirt out very fast! If there air in this joint, you will probably hear a very little bubble and squirt sound when it comes out.


CC

[txm123]

I tried the steps you mention ,but the problem is that in step 1 I can´t get pressure to start bleeding .
i heard about using a syringe and a vacumm cleaner to take out the air inside the line,what do you think? In youtube I saw a few DIY videos ,but I think maybe its worst the remedy than the pain