Author Topic: Brake fluid won't start to flow. (Read 14576 times)

mycb750k6 · « **on:** September 17, 2009, 11:58:03 AM »

I'm not a patient person so we can start there. I've rebuilt the master cylinder, brake caliper, new braided steel lines, new banjo washers new brake pucks. I think that's about it but I can't get the fluid to start to flow. The master cylinder stays full. All the component parts have been either cleaned thoroughly or replaced. Is this normal? I'm starting to become annoyed.

mgbgt89 · « **Reply #1 on:** September 17, 2009, 12:03:22 PM »

Check the tiny hole in your master cylinder. 90% guarantee it's plugged. Use a small pin, or guitar string to unplug it.

BVCB650 · « **Reply #2 on:** September 17, 2009, 12:05:28 PM »

You probably have an air bubble in the line. Trying to work it down will take time.

Gordon · « **Reply #3 on:** September 17, 2009, 12:07:46 PM »

You may need to prime the master cylinder. Bryanj gave a good, quick write-up on one way to do this here:

http://forums.sohc4.net/index.php?topic=46891.msg492278#msg492278

BVCB650 · « **Reply #4 on:** September 17, 2009, 12:28:55 PM »

It's usually called bench bleeding. I didn't do mine after the rebuild. Took about 10 minutes to get the embolism worked down.

flybox1 · « **Reply #5 on:** September 17, 2009, 01:42:33 PM »

yes, check the tiny hole in the bottom of the MC for blockage.
also try this:
Turn your handlebars all the way to the left. get a 4' section of surgical tubing and connect one end to your right handlebar and the other to your bleeder screw. open your bleeder screw, squeeze your front brake lever and rubberband it to your handle. start (lightly) tapping all the connections/elbows/banjos between your MC and calipersto free up the bubbles. start at the caliper. Have a beer, or 2. come back in an hour, tap again and repeat, have another beer, come back to refill your MC as the fluid flows into your lines.
once the surgical tubing fills up to your MC height, turn off your bleeder valve and clamp off the tube right above it.
remove the tubing from your bike, pour the excess back into the bottle or dispose of if its dirty.
clean up spillage (simple green) as it will remove paint. top off your MC, and you should be good to go.

if your brakes are still spongy, turn your bars to the left and open your MC, CAREFULLY squeeze your brake, or you'll have fluid on your ceiling

and secure it in place. tap connections as stated above to release any small bubbles, drink the rest of your beers, and check it in the morning. repeat (not the beer part) until no longer spongy.

FB1

mycb750k6 · « **Reply #6 on:** September 17, 2009, 04:06:09 PM »

OK so here's the deal. If I hold my MC in my hand with no hoses or brake lines attached and put fluid in it, shouldn't I be able to squirt fluid all over the garage when I squeeze the handle? Because I can't. It just makes squishing sounds. I stuck a wire in the hole at the bottom with the handle completely pulled and was able to poke a wire in there but that had no effect. It's like a little pump but it doesn't want to prime and start pumping.

scondon · « **Reply #7 on:** September 17, 2009, 04:44:05 PM »

Quote from: mycb750k6 on September 17, 2009, 04:06:09 PM

OK so here's the deal. If I hold my MC in my hand with no hoses or brake lines attached and put fluid in it, shouldn't I be able to squirt fluid all over the garage when I squeeze the handle?

Have you primed it according to the instructions in Gordon's link? If not, then it won't pump fluid.

BVCB650 · « **Reply #8 on:** September 17, 2009, 04:58:07 PM »

The cup on the piston may have turned inside out.

mycb750k6 · « **Reply #9 on:** September 17, 2009, 05:31:42 PM »

Yes I read it....
First WEAR GLOVES and cover everything
Remover banjo bolt and pipe from master a put gloved finger over outlet
pull in lever and whilst holding in lift finger from outlet and replace
let go lever and pull in and hold again lift and replace gloved finger
keep repeating until master cylinder builds pressure and fluid squirts out under finger (thats why you cover everything!!!)
whilst holding in lever reconnect pipe with banjo bolt and now bleed via bleed nipple

In doing this I eventually feel pressure under my thumb and air rushes out when I remove my thumb but I wouldn't say fluid squirts out under my finger as he describes. There is some that comes out but I was expecting a squirt of fluid. Why do I have to go through this? I don't see anything in the manuals about holding in the handle while reconnecting the banjos. I don't get it.

And how in the heck would the rubber get inside out in there.?

750goes · « **Reply #10 on:** September 17, 2009, 05:37:39 PM »

You are pushing fluid, so it stands to reason when you release the lever it will SUCK any pushed fluid back in.....
The rubber cup can also be worn to the extent that it rolls back and forwards and won't push fluid under pressure.

How was the m/c before doing all this - soft or spongy - does it leak from behind the lever - on top of the piston ?

Only trying to assist......

Spanner 1 · « **Reply #11 on:** September 17, 2009, 05:49:22 PM »

The tiny fluid return hole is still blocked....it's the hole nearest the banjo fitting. It appears like it's the same size as the other hole but it is cone shaped and narrows down to a tiny opening into the front of the cylinder just a fraction in front of the piston seal...so do not pull the brake lever when working a very small sewing needle into it to clear it...brake cannot 'prime' until clear.....when clear and fluid in the system, on releasing the brake lever a 'spurt' of fluid will be visible up from this hole when you let go the brake.....

mycb750k6 · « **Reply #12 on:** September 17, 2009, 06:02:32 PM »

OK I'm going after that front hole next. I just rebuilt the MC and put the parts in in the correct order and orientation but they did seem to want to flip around and not stay in the correct orientation as they were going in. Who knows. So when I do the pin thing in the front hole, how far should it go, 1/2 inch?

Spanner 1 · « **Reply #13 on:** September 17, 2009, 08:39:04 PM »

It will just drop into the taper but the last 1/32" ( guess!) will be the blockage...the taper on the sewing needle ( #1, the smallest one ) will stop it ( needle ) from going too far as you don't want to enlarge the hole any.....in other words, I wouldn't use a shirt pin.

tlbranth · « **Reply #14 on:** September 17, 2009, 08:51:47 PM »

I had the same problem. The holes weren't blocked. One of the members here (an Aussie as I recall) posted a fix which worked like a charm. Hook a clean hose to the bleeder. Open the bleeder. Suck like mad on the hose and close the bleeder while there's still vacuum in the system. Wait a while and the mc will be primed. Tried for a week with no luck 'til this little gem came along. Good luck mate.

drumgod · « **Reply #15 on:** September 17, 2009, 09:07:41 PM »

Quote from: mycb750k6 on September 17, 2009, 06:02:32 PM

...I just rebuilt the MC and put the parts in in the correct order and orientation but they did seem to want to flip around and not stay in the correct orientation as they were going in. ...

I'm not sure if this is your problem but maybe you should double check your assembly against this info in this thread?

http://forums.sohc4.net/index.php?topic=53812.0

I know I was a bit confused about the "secondary cup" placement... It needs to slide onto the piston. Not in front of the piston like it is pictured in some manuals.

I just rebuilt the master cylinder and caliper on my CB550K and it primed, pumped and bled in about 20 minutes. All I did was put fluid in the reservoir and slowly pump it through the system. (with a long piece of tube on the bleeder)

Spanner 1 · « **Reply #16 on:** September 17, 2009, 09:44:29 PM »

tlbranth, with respect, ya wouldn't have been able to suck any fluid into the tube if the tiny fluid hole was blocked...it's the only passage for fluid to enter the system from the reservoir, so yes, in your case the hole was not blocked !!

Steve_K · « **Reply #17 on:** September 18, 2009, 05:24:47 AM »

My 550 would not pump either. No fluid moved when pumping. I removed the brake lever. I opened the bleeder on the caliper and put my bleeding hose on it. With the lever off, I used a screwdriver to push the piston to the end of it's stroke. Fluid flowed up in to the MC cup and I closed the caliper bleeder screw and put the lever back on.
That said I have used the other methods mentioned. I would have moved the caliper closer to the handle bar end in order to get more travel at the lever, but my set up would not allow that.
Brake bleeding is the biggest pain for when working on these bikes.
Steve

BVCB650 · « **Reply #18 on:** September 18, 2009, 05:33:56 AM »

Quote from: mycb750k6 on September 17, 2009, 05:31:42 PM

Yes I read it....
First WEAR GLOVES and cover everything
Remover banjo bolt and pipe from master a put gloved finger over outlet
pull in lever and whilst holding in lift finger from outlet and replace
let go lever and pull in and hold again lift and replace gloved finger
keep repeating until master cylinder builds pressure and fluid squirts out under finger (thats why you cover everything!!!)
whilst holding in lever reconnect pipe with banjo bolt and now bleed via bleed nipple

In doing this I eventually feel pressure under my thumb and air rushes out when I remove my thumb but I wouldn't say fluid squirts out under my finger as he describes. There is some that comes out but I was expecting a squirt of fluid. Why do I have to go through this? I don't see anything in the manuals about holding in the handle while reconnecting the banjos. I don't get it.

And how in the heck would the rubber get inside out in there.?

The part of the cup that goes on the piston has that thin edge that can roll as you are putting the guts back in the MC. That's why you lube the cylinder with brake fluid before assembly.

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Author Topic: Brake fluid won't start to flow. (Read 14576 times)