How do you bleed these rear brakes?

[RangaBlitzFanga]

I can do it on a bike with a seperate master cylinder no problem. But these chinese ones have me stumped

I replaced the entire rear brake assembly with a new one that came pre-filled with fluid. It worked fine but the cable is a bit too long and goes off the master cylinder to the right, creating a nice little loop to catch any sticks and crap in the way. I loosened the nut on the master cylinder and turned it around to the left so that the loop is between the swingarm and master cylinder, won't catch anything that way. I likely let some air in doing that as the brake still worked but it was quite weak

So I decided to bleed them today, and the end result is no rear brake
Here's the processes I tried
Method 1:
- Took the master cylinder off the bike and held it down low (since air rises to the top, i figure its more inclined to go towards the caliper and out the bleeder)
- Attached a 80cm hose to the bleeder and into a bottle
- Made sure the master cylinder was as full as possible, then pushed it down by hand into the ground (about 1/3-1/2 way)
- Slightly loosen bleeder until fluid stops flowing
- Tighter bleeder then release master cylinder
- Repeat above 3 steps until fluid colour changed completely

It took about 10-15 pumps to get new fluid colour start coming through. The first pump had 3-4 very small bubbles. After about 15 pumps there were big bubbles. Brake worked but even weaker than before. Argh... time to try method 2

Method 2:
- Raise master cylinder up high so the brake line always travels up
- Attach hose and syringe full of fluid to bleeder
- Open bleeder
- Start pushing some fluid through (didn't get far)
- Close bleeder
- Pump brake a few times
- Open bleeder again
- Now can push fluid through uninterrupted, kept pushing fluid through
- When full, empty master cylinder of fluid
- Repeat above 2 steps several times
- Close everything back up and remount brake

Now... NOTHING, no resistance at all. I've used both methods with great success in the past. But this hasn't worked and i'm stumped. I'm sure air is getting in somewhere but surely the brake should still work!? i've only loosened it from the master cylinder end, havn't touched the caliper

Help? Please

 

[rotn50]

The china rears are like no other mate, i disconnect the hose from the master cylinder and the caliper, fill the MC up and bleed it and also check for good pressure, then install the hose on the MC and then bleed the hose by holding the hose and letting air out as you pump the MC, once good pressure it coming thru the hose and the fluid is dropping on the MC then fill the caliper up with fluid and quickly install the banjo and whack it on the caliper. without pushing the brake lever crack the caliper nipple and if the fluid bleeds then it good to let bleed for any little bubbles, if it sucks back in then do again. I have not come across a more of a ******* system to bleed then these chinas.

 

[RangaBlitzFanga]

I think I understand the caliper
So with the hose out of the equation, pouring fluid into the caliper would push air out the top where the hose connects? theoretically it should have no air bubbles in it (this done with it on the bike?)

But I don't get the master cylinder part. How can I possibly check for air in it? just fill it up and pump till it goes out the hose end?

Ok so connect cable to master cylinder, hold the caliper end of the cable up in the air? (there would be a loop though, as the cable comes off the master cylinder facing down)
more pumps until fluid comes out the top? I suppose then if I have the master cylinder full and cap off the filler, it has no way of letting fluid out/air in (like holding a straw full of fluid and putting your finger on 1 end, it stays in there) and so shouldn't leak out when I face it towards the ground again. Though a couple drips WILL come out creating a small air bubble when re-attached to the caliper

How do I get that last little air pocket out? bleed with method 1 or just leave it mounted to the bike and pump it through a bleeder a few times?

 

[zorro]

Do it like a hydraulic clutch on a car;

- Empty the master cylinder, open the bleed nipple and pour clean fluid in until it runs out the nipple clean.
- tighten nipple and fill MC with fluid
- pump 10 times and hold down whilst cracking the nipple, close nipple.
- top up fluid
- repeat until all air is out of line and you will have a good pedal.

Keep it simple, and fwiw works on any atomik and no name china I've had the joy to work on

 

[DHZ_XR8cing]

I found the best way to do it is to take the brake system off the bike.
Mount the master cylinder up high.
Have the caliper straight bellow.
Use a big syringe with some hose fitted to it.
Attach it to the open bleed nipple.
Pump the fluid up until the master is full.
close nipple.
remove hose.
use a screw driver to pump the master. Dont crack open the nipple unless you have the master depressed which forces the fluid out and dont let the air in.

The biggest problem with doing it on the bike is air dont like to go downwards to bleed out the nipple and the hose near the master where it coils slightly seems to hold the air.

 

[RangaBlitzFanga]

i'm curious as to whether there's any pockets that air can hide in. I mean i've already done the master cylinder up high with a continous uphill on the line as I push fluid through. That so far has been the worst, with no resistance in the brake at all.

Is it possible i've busted something? I don't see how, as i've put less pressure on the MC than the lever provides normally, and going the opposite way it's only a 60cc syringe, I can't pump it THAT hard

 

[rotn50]

To check the MC, remove both caps and fill them up, put your finger over the banjo hole tight and start pumping, if you cant stop the pressure squirting out the MC is good and operative, the rears can be very hard to bleed mate and sounds like all us giving advice do it different haha. Take ya pick and i hope you get it.

 

[needapitty]

ive had big problems trying to bleed my china rear's

but ill give a few of these ways a go and see if i can get them to work again...

 

[RangaBlitzFanga]

i'll give it a go tomorrow. I know one thing for sure, once this thing is bled, it's never getting done again

 

[DHZ_XR8cing]

Once you work out the art of it you will be more confident next time. The first time I did it took me hours. Each time I have done it Its getting quicker.

The air can get trapped in the line and just move back and forth. Thats why its important to try to bleed them one way.
Pumping the fluid up from the caliper is the best way. When bleeding while holding the pressure on the master crack and tighten both ends of the line.

 

[RangaBlitzFanga]

I'll give your method a go first as it seems the most logical to ensure there's no air in the line whatsoever.

I'll start by pumping all the fluid out the bleed nipple leaving an empty line. So just to make sure
Master cylinder held up high and keep it straight? i.e. filler cap points upwards
Caliper.... keep it straight (as it were on the bike) OR dangling so the line becomes the highest point of the caliper?
No pumping at all, just fill it up through the bleed nipple with a syringe, when MC full, close it off.
Refit to bike and pump the lever and fingers crossed feeling will return and brake operates properly

Not sure how you mean pump it with a screwdriver, hows that work? i'd normally just grab the master cylinder with both hands and squeeze it, though not enough leverage to fully compress it

 

[RangaBlitzFanga]

problem solved. There was nothing wrong with my method, there was however something wrong with the bleed screw

I reconnected the syringe and noticed if I pushed nothing but air into the bleed nipple when its closed, I could hear a slight bubbling of fluid. The actual bleed screw itself was not seating properly, even when tightened right down. Air and fluid could get through the thread
So I smeared the thread with gasket sealant, screwed it in and let it set. Tried opening and closing it several times, no air leak!

I don't know what method worked best but I did them all to ensure no air in. Even pumped fluid back n forth with the syringe to dislodge any bubbles. Seems to be free of air now, hopefully no more leaks!

 

[headsmess]

heh heh heh, the old mechanical failure strikes again!

pays to strip china brakes, wash with metho or brake fluid only. check for burrs and gremlins...

same goes for just about every part on almost every bike in reality. shame that everything mechanical even...jeesus. my life consists of constant teardowns!

 

[RangaBlitzFanga]

i've never once had to fix a bleed nipple on any other machine. I've never even fully removed one so wasn't sure if there was supposed to be a rubber gasket or some such behind it (I would have thought so, who'd think metal on metal is a good seal?)