Bleeding Front Brake

swooshdave · Mar 21, 2015

I can not get my front brake to respond at all.

Short version, I had a short hose with the clippers on it and last fall took it off. Went to regular bars and put the original rubber hose on. It didn't work very well so I didn't ride it. Got a new bake line I'm trying to bleed it.

I've read all the posts on bleeding. I've tried a MityVac to pull from the bleeder. I've used a syringe and push the fluid up to the master cylinder. At no point can I get the master cylinder to respond at all. The lever is completely flaccid.

Fluid is definitely moving freely through the system.

The one thing I changed was to move the brake light switch to the inboard port. Does it make any difference which port the brake line is in?

kerinorton · Mar 21, 2015

Try pushing both pistons back. That should dump the air back into the master cylinder. Keep doing that till you have all the air out. Keep the master cylinder bleed hole as high as it can go, Ie turn the bars to the left.
Dereck

swooshdave · Mar 21, 2015

I was hoping not to have to pull the caliper off but I guess I'm going to have to. I just don't get why I get almost no pressure at the lever.

ashman · Mar 21, 2015

This happened to me once and what I did was to crack open the nut on the top line which comes out of the M/C and bleed that first. see if this makes your lever work, if it does then the fluid should go down to the calipar, also check to see if your rubber hose is not blocked, the rubber swells up and fluid won't get throught.
Ashley

swooshdave · Mar 21, 2015

ashman said:
This happened to me once and what I did was to crack open the nut on the top line which comes out of the M/C and bleed that first. see if this makes your lever work, if it does then the fluid should go down to the calipar, also check to see if your rubber hose is not blocked, the rubber swells up and fluid won't get throught.
Ashley

How do you bleed the top nut? Just loosen it and let fluid out?

It's a brand new ss line, no swelling.

gtsun · Mar 22, 2015

Have you tried pulling the lever closed & leaving it that way overnight? That's the only way I got my stock (sleeved) MC to bleed. I used a zipp tie.

kerinorton · Mar 22, 2015

gtsun said:
Have you tried pulling the lever closed & leaving it that way overnight? That's the only way I got my stock (sleeved) MC to bleed. I used a zipp tie.

Theoretically that shouldn't work, because you block off the relief port.

kerinorton · Mar 22, 2015

Presuming you can open the bleed nipple. With the m/cy full and at its highest position, gravity should allow the brake fluid to pass through to the caliper. Put a plastic hose on the bleeder and hold it up by the bars. Go have a beer and come back every so often to check it out.
All this should work provided the relief port in the m/cyl isn't blocked, You should be able to detect brake fluid moving in and out of this port when you agitate the brake lever. If not, maybe the lever is holding the piston in too far and blocking the port. It should not be that hard to bleed using the above techniques I have mentioned..
Dereck

Diver3284 · Mar 22, 2015

I had the same problem after fitting Madass's Tokiko caliper/disc upgrade. After a lot of mucking around I did this: 6 -8 pulls on the lever, wait 30 seconds, open bleed nipple. Repeat. And repeat. After about 6 reps I got resistance/feel, and after about another 4 I had a good brake. Don't ask me why/how (I'm a Lawyer

) but it worked for me.

toppy · Mar 22, 2015

kerinorton said:
gtsun said:

Have you tried pulling the lever closed & leaving it that way overnight? That's the only way I got my stock (sleeved) MC to bleed. I used a zipp tie.

Click to expand...

Theoretically that shouldn't work, because you block off the relief port.

If you look closely at the pistons when releasing the lever you may see that they retract into the caliper noticeably instead of just remaining in position but releasing the clamping force applied to the pad. This gives the spongy feel and long lever travel as the fluid pushed out of the master cylinder must first move the pistons to the pad an then you have normally run out of lever travel before enough clamping load can be applied.

Holding the lever on overnight helps the rubber seals to settle with the piston against the pad as it should be. As it is drag between the piston and its seal (instead of the piston being able to move in the seal) that means the seal is gripping the piston and being compressed as piston moves out then as pressure is released the seal returns to its normal point taking the piston back with it.

Mr.Sparks · Mar 22, 2015

I had the same problem and spent two days on it. Stripped and rebuilt the MC, no change, stripped and rebuilt the caliper, no change, eventually sorted when I got the pistons and pads hard against the disc (manually) then injected the fluid with a syringe from the bleed nipple. Was able to bleed it in 5 minutes after that.

swooshdave · Mar 22, 2015

Mr.Sparks said:
I had the same problem and spent two days on it. Stripped and rebuilt the MC, no change, stripped and rebuilt the caliper, no change, eventually sorted when I got the pistons and pads hard against the disc (manually) then injected the fluid with a syringe from the bleed nipple. Was able to bleed it in 5 minutes after that.

Trying that next.

ashman · Mar 22, 2015

swooshdave said:
ashman said:

This happened to me once and what I did was to crack open the nut on the top line which comes out of the M/C and bleed that first. see if this makes your lever work, if it does then the fluid should go down to the calipar, also check to see if your rubber hose is not blocked, the rubber swells up and fluid won't get throught.
Ashley

Click to expand...

How do you bleed the top nut? Just loosen it and let fluid out?

It's a brand new ss line, no swelling.

If you open the nut a little and move the lever it will show sign of any air bubbles there and if its straight fluid it should work, but for some reason after doing that to my M/C it started to work and push the fluid down to the caliper, then it bleed the nomal way after doing that.

Ashley

BrianK · Mar 22, 2015

kerinorton said:
gtsun said:

Have you tried pulling the lever closed & leaving it that way overnight? That's the only way I got my stock (sleeved) MC to bleed. I used a zipp tie.

Click to expand...

Theoretically that shouldn't work, because you block off the relief port.

But it does. Dave's issue sounds more profound though.

Tried moving the switch back, just for grins, Dave? From memory, only one of those ports actually opens/closes with the lever.

swooshdave · Mar 22, 2015

Fluid is clearly moving through the port.

BrianK · Mar 22, 2015

Port opening correctly? If you reverse bleed from the caliper, does fluid fill up the MC?

swooshdave · Mar 22, 2015

BrianK said:
Port opening correctly? If you reverse bleed from the caliper, does fluid fill up the MC?

Yes.

BrianK · Mar 22, 2015

Fluid leaks?

I couldn't see any last time I went through this but ended up having Fred at Old Britts build me a new standpipe for the caliper. This problem came out of nowhere; never had any problem til the MC clogged and locked the caliper. Then it was a shitshow. Best of luck Dave.

worntorn · Mar 22, 2015

Dave, you might have air sucking back into the system somewhere when bleeding. I recently had this problem after fitting a new hose on my MK3 rear brake. I tried to reuse the copper sealing washer and that did not work. On bleeding, a continuous supply of air bubbles came through even after refilling the MC many times. The leaky washer allowed air to suck back in on the return stroke of the MC piston, but it did not leak brake fluid at any time. After changing to a new copper washer, the brake bled as normal, pedal firmed right up.

Are you using a clear plastic tube on the bleeder so that you can see if air bubbles are flowing through?
If you only get mush on the lever, then there is likelihood of either an air leak or trapped air.

Glen

swooshdave · Mar 22, 2015

worntorn said:
Dave, you might have air sucking back into the system somewhere when bleeding. I recently had this problem after fitting a new hose on my MK3 rear brake. I tried to reuse the copper sealing washer and that did not work. On bleeding, a continuous supply of air bubbles came through even after refilling the MC many times. The leaky washer allowed air to suck back in on the return stroke of the MC piston, but it did not leak brake fluid at any time. After changing to a new copper washer, the brake bled as normal, pedal firmed right up.

Are you using a clear plastic tube on the bleeder so that you can see if air bubbles are flowing through?
If you only get mush on the lever, then there is likelihood of either an air leak or trapped air.

Glen

I don't trust the washers on the hose at the master cylinder. If I was smart I'd change them out with new ones. :mrgreen:

Logic would say that if you have a leak in a hydraulic system that you would have fluid escaping. But sometime we have to set aside logic for practical expirence.

Bleeding Front Brake

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