Help with brake bleeding!

today i replaced my front brake line on my yz125 with a braided line and rebuilt my MC. I tried to back bleed the line, but as of now i have no pressure at all. I can hear fluid moving in the caliper but i cant get the pistons to move at all...

Is there a special technique required when filling a MC/line/caliper that was 100 percent dry?

It's a very long process but just keep pumping that brake lever and crack the bleed nipple letting a little bit of fluid out at a time and tighten back up. Will take forever and go through a lot of brake fluid but eventually you will start pushing air out of the system.

Try back bleeding , air is trapped in the line .

I just rebuilt my calipers yesterday.  First make sure the pistons are pushed all the way back, which I am guessing you did.  Then leave the banjo bolt screwed very loosely in the caliper with a bucket under it.  Then fill your MC with brake fluid.  If you squeeze the brake quickly a few times then let it sit, the fluid will start draining from the MC.  You can then top it off and pump some more fluid through.  This will fill the line and the MC plunger, and fluid will be coming out of the loose banjo bolt.  Top off again, snug up the banjo bolt and open the bleeder valve with a hose on it.  I loop the hose up and over the cable holder on the fork protector and down into a bucket.  Just keep that MC full and let some fluid work through the system.  Close the bleeder and you should start getting pressure when you pump the brake.  Again, keep the MC full.  Then the bleeding process begins, which you know how to do.  After the initial bleed, seal the MC cover, zip tie your brake lever to the handle bar and walk away for a while.  Over night is the best.  Then go back out, cut the zip ties and you will feel a lot of pressure, but take the time to remove the MC cap and bleed again.  You will be surprised how many micro bubbles come out of the bleeder valve.  It's a longer process, but when you are done, your brakes will be solid.  Just make sure your front wheel spins normally when you are done, and don't overfill the MC.  There is a fill line, and that is as high as you should go before sealing the MC cap for the last time.  Whatever method you use, let us know how it goes.  

Disclaimer: I am a lame mechanic. But I bought a $9 Tusk brake bleeder and I have had to use it 3 times on 3 different bikes. Worked perfectly each time- I would look into it. Hook it up, open the valve, pump the brakes keeping fluid in the master cylinder. When you stop seeing bubbles pass through the 1-way valve, you are done.

rent or buy a brake kit from your autoparts store...the problem is the piston in the MC is very small and pushes a very small amount of fluid, making it very difficult to get those bubbles out, also you need to push the fluid From the brake up into the MC.

 

You can TRY pushing a bubble DOWN and out and eventually after about 6 hours of pulling on the brake you MIGHT be successful.

 

there was a guy that used a turkey needle and just pushed a giant amount of fluid up and out.

 

Also someone tapping on the components and line as you push the fluid helps to remove trapped air bubbles.

 

personally i would do the turkey needle

I once installed one of the seals backwords in the m/cyl.and it was impossible to get it to bleed. Just something to consider. Pushing the fluid up the line is necessary on some bike. A big syringe with some small clear hose works. Steal moms or your wifes turkey injector!

got all kinds of gadgets and still just use a hose and a jar,

I once installed one of the seals backwords in the m/cyl.and it was impossible to get it to bleed. Just something to consider. Pushing the fluid up the line is necessary on some bike. A big syringe with some small clear hose works. Steal moms or your wifes turkey injector!

 

Don't the open end of the seals point out like this?     ]    [  while on the MC push rod?

Beside the fact that brake bleeding is a PITA I am worried I might have put one of the seals in wrong. 

Just looked at my honda manual and they go ]] with lever on the right. Check your model on an exploded diagram like bike bandit.

Just looked at my honda manual and they go ]] with lever on the right. Check your model on an exploded diagram like bike bandit.

been having a hard time finding a clear diagram of the parts. Its a 2001 yz 

lean the bike over on its left side, and bleed. When bleeding, pull the lever in, and let it SNAP back. That will help release any air trapped in the master, and at the banjo bolt. Every once in a while, give the caliper a couple knocks with a mallet, and wiggle the lines around to help release any trapped air

Back bleed: remove the caliper, with the pads in, use compress air to extend the pistons. Top off the fluid in the caliper.  Reconnect to the brake hose, then pry the pads apart forcing the fluid back up the hose to the MC.  Install the caliper and operate the lever to extend the caliper pistons until the pads contact the rotor.

I use a big 60 ml syringe and a short piece of clear plastic tubing and pump the fluid in from the caliper.  Bang on the caliper while doing it.  Also I use a vibrating tool, like an orbital sander with no paper, on the lines.  You need to break loose the bubbles.  Wrap the bleeder valve with teflon tape so it doesn't leak.  

I see you live in Idaho, they must have Murdoch's there.  They sell big syringes in with the horse stuff.   

parts should show up tomorrow and then i will try and back bleed again. 

I had the same issue when I replaced my front brake line... Never could get it to firm up... Only thing that worked with me holding the brake lever in and  a buddy tapping on the line starting at the caliper and working up to the MC... I could see the trapped bubbles coming out.... After we did that a couple of times I was able to bleed like normal...

Man I use a empty water bottle, poke a hole in it with a fuel line sticking out of it and put it on the nipple. I press the brake as hard as i can and release the pressure tighten back up and repeat. Brakes become solid as a rock no air. Oh and make sure u fill resivior every time u tighten that nipple, or all u will be doing is putting air back in the system. 

Back bleeding can also be done with a syringe. Force the fluid in thru the bleeder, watch the reservoir as it will overfill.

Also regarding conventional bleeding. For years I was taught to pump the brakes or clutch, hold pressure on the system and then release the bleeder quickly and retighten before letting pressure off of the lever/pedal. I have since been told to release the bleeder and gently squeeze then retighten. I have tried it both ways and believe better results are obtained quicker using the second technique (not pressurizing the system prior to opening the bleeder)

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now