Front Master Cylinder Bleeding

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swooshdave

swooshdave

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This was pulled from the build thread.
combat-proddy-build-t4186-240.html?hilit=brake#p74605

swooshdave said:
Coco said:
swooshdave said:
Next problem is that we can't get the brake to work right. Everything is new with a sleeved master cylinder. Lever goes back to the grip. Pistons are moving. Fed fluid from the bottom, then tried regular bleeding. Hasn't changed. Not firm. Sigh.

Seat is finished. I'll update the other thread.
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You may still have air in there caught up somewhere. Have you tried a cheap brake fluid vacuum pump? I use large syringes from the vet supply store since I'm too cheap to buy a vacuum pump. I was in your situation and almost got the pump but just bled a few more times and that did it.
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I do have a vacuum pump, but I can't find it. I need to pull the Bultacos out of the way and look some more. How do you use the vacuum pump on the Norton?
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I found the vacuum pump and bled the crap out of the brake. It's also been bled from the bottom using a syringe that comes with the master cylinder. I then talked to Al Miles who did the master cylinder sleeving. He said there is air trapped in the caliper, especially since I was going from a dry system (as you know I had rebuilt or replaced every part on the brake). He said one guy sat there and pumped the lever for half an hour or something. If I wasn't dicking around with the ignition I probably would have. He also said to make sure the pads were against the disk by applying air pressure to the caliper (then sealing it up and bleeding). Did that. I've even took off the master cylinder and propped it up so it was the highest point. And also tried the "tying the lever back overnight" trick.

No matter what I've tried has improved the feel. So now I have to ask, is this the proper range for a sleeved cylinder? It does lock the brake so at least it functions.

[video]http://www.youtube.com/watch?v=9Z_M9sX6Zrc[/video]
 
My master cylinder is not sleaved, but that movement looks excessive to me. Not sure on the syringe comment above, but what I did when I rebuilt my caliper, was to remove both the rigid line and the bleeder from the caliper. Then I took a plastic syringe and modified the tip to accept the red straw out of my WD-40. I used the staw to reach as far as possible inside the bore and squirted brake fluid in there until it was running out. I then had no problem bleeding the rest of the air thru the master cylinder. It was a little squishy at first, but soon firmed up well. My idea was to let the fluid rise from the bottom of the caliper to push the air out, rather than trap a bubble in there.

Russ
 
rvich said:
My master cylinder is not sleaved, but that movement looks excessive to me. Not sure on the syringe comment above, but what I did when I rebuilt my caliper, was to remove both the rigid line and the bleeder from the caliper. Then I took a plastic syringe and modified the tip to accept the red straw out of my WD-40. I used the staw to reach as far as possible inside the bore and squirted brake fluid in there until it was running out. I then had no problem bleeding the rest of the air thru the master cylinder. It was a little squishy at first, but soon firmed up well. My idea was to let the fluid rise from the bottom of the caliper to push the air out, rather than trap a bubble in there.

Russ
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I might try that.
 
Using all the strength in my hand, I can pull the lever of my MkIII's 13mm sleeved master cylinder about half way back to the grip.
 
Dave, fwiw I have a stock master cylinder and my brake lever doesn't pull even half that distance, brake contact is almost immediate. I just bled mine this spring and had the caliper off and kept turning it at odd angles while bleeding and it ended up solid on pull.
 
britbike220 said:
Dave, fwiw I have a stock master cylinder and my brake lever doesn't pull even half that distance, brake contact is almost immediate. I just bled mine this spring and had the caliper off and kept turning it at odd angles while bleeding and it ended up solid on pull.
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That is another option I need to look at.
 
I lightly tapped each part of the brake system starting from the lowest point and going to the highest, caliper, brake lines, master cyl. helping any air that was clinging to brake free. Then left overnight with lever held open. Lever now has very little movment.
 
Dave
I had exactly the same problem when I rebuilt the caliper and had the master cylinder sleeved. I tried everything anyone suggested and still had air in the system. Finally someone suggested that I turn the handlebar all the way to the left, elevating the master cylinder to the highest point, then just leave it alone for a few days and work on something else. The air bubble would slowly work its way to the highest point and out of the system. It worked. After several days the brake lever acted normally and the brake action is way better than before. If you've tried everything else, give this a try. Good luck!
Tim
 
Left the handlebar to the left for several days (at least 5) with no luck. The bad news is that it's still not right, the good news is that others have had this exact same issue and it worked out for them. I'll keep at it.
 
hi dave
you say you have put the brake pads onto the disc. how about pushing the pads right back into the caliper, there would be less air to get out. then put sort of packing to keep the pads right in while you bleed it.
 
Lever is way too much motion as already mentioned. Also something more wrong that just air as squeezing lever that far and fast w/o cap on should jet brake fluid all over the place and paint. Once you figure out what there is no jet, like not grinding the right amount off lever peg that pushes on piston or oil ring missplaced, I put zip tie on level held back with bar turned to put m/c highest then leave over night to let the tiny train of bubbles adhering to hose and surfaces to crawl up and out.
BTW if this intermediate peg in not cut down far enough when summer heat or heavy use swells brake fluid it can cause brake lock up. On the road can take off level and grind down peg on cement till it releases lock up in high heat then ride on.
 
Dave, I go along with britbike220. Take the caliper off and hold/swing in all sorts of positions while bleeding. Amazing what air still comes out. Have plenty of brake liquid at hand though. Did all this at the rear caliper (Mk3) recently, have to step on the pedal with care now to avoid skidding the rear wheel. Good luck.
 
KEV-C said:
hi dave
you say you have put the brake pads onto the disc. how about pushing the pads right back into the caliper, there would be less air to get out. then put sort of packing to keep the pads right in while you bleed it.
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This is what Al told me to do. His master cylinder kit, I'll go with what he says first.
 
hobot said:
Lever is way too much motion as already mentioned. Also something more wrong that just air as squeezing lever that far and fast w/o cap on should jet brake fluid all over the place and paint. Once you figure out what there is no jet, like not grinding the right amount off lever peg that pushes on piston or oil ring missplaced, I put zip tie on level held back with bar turned to put m/c highest then leave over night to let the tiny train of bubbles adhering to hose and surfaces to crawl up and out.
BTW if this intermediate peg in not cut down far enough when summer heat or heavy use swells brake fluid it can cause brake lock up. On the road can take off level and grind down peg on cement till it releases lock up in high heat then ride on.
Click to expand...

This is not a stock master cylinder so it may not get the squirts.
 
I just checked on my sleeved front master cylinder, there is a build-up of a squirt when pulling the lever. Had a better look on your video, the surface of the oil is dead still. Might pay to check how much oil the cylinder actually pumps towards the brake (with a clear hose on the air vent), and than if holes in sleeve line up with holes in cylinder. But maybe you have been through all that already.
 
slimslowslider said:
I just checked on my sleeved front master cylinder, there is a build-up of a squirt when pulling the lever. Had a better look on your video, the surface of the oil is dead still. Might pay to check how much oil the cylinder actually pumps towards the brake (with a clear hose on the air vent), and than if holes in sleeve line up with holes in cylinder. But maybe you have been through all that already.
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My guess is the sleevings can be different. Al said there like four or more seals in his setup. That might prevent the blowback.

Since the brake functions, just is soft and fluid moves through the system I assume there is no hole alighnment issue.
 
swoosh,sleeving gives the brake more"feel" the lever comes back much further than a std setup,try sqeezing a piece of 2x2 wood to see how the std setup feels,after all you,ve done you still think theres air in the system try this,leave it alone for an hour,first pull will come back to the bars second not quite and so on,
 
My sleeved Lockheed m/c jets fluid. Might help if you check with vendor what is expected from your custom m/c. Old swollen hose can feel soft but assume that is not the instant case. I zip tie my lever to grip with bars turned to rise m/c and leave in over night to let the adhering bubbles slowly crawl out and disperse. So far seems to give me full solid connection of effort to effect. Even filling from bottom up can't eliminate these tiny bubbles that still can add up to enough volume to annoy.
Vibration can help shake them loose but they still take their sweet slow time to rise and disperse. Hope that's all you issue is.
 
chris plant said:
swoosh,sleeving gives the brake more"feel" the lever comes back much further than a std setup,try sqeezing a piece of 2x2 wood to see how the std setup feels,after all you,ve done you still think theres air in the system try this,leave it alone for an hour,first pull will come back to the bars second not quite and so on,
Click to expand...
That's what it does!
 
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