Motorcycle Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
I have an 81 CB750C that I got as part of a trade deal. The bike had been sitting for a few years. All original. 7K miles. When I got it, the calipers were stuck, and you couldnt move the front tire. Got it home, pulled the calipers, cleaned them, didnt change anything. The rubber and pistons looked good. Threw them back on the bike, and before I attached the lines, I put the lines in a bottle and pulled the brake to verify that fluid is getting to the calipers. All looks good. I reattached the brake lines to the caliper and bled the brakes. The bike is on a bike stand, and I spun the tire and pulled the brake. It kept spinning. I pumped the brakes a few times, and then it stopped. I bled them again, and same thing....you have to pump the brakes before they actually kick in. I changed the master cylinder, bled the brakes, and same deal. I pump them 2 or 3 times before they work. :confused::confused::confused:

since doing brakes is all new to me...what am I missing??
 

·
Member Map
Joined
·
23,911 Posts
There is still air in the system most likely. Motorcycle hydraulic systems are notorious for keeping a pocket of air up near the banjo bolt, even after a good amount of fluid is pumped through the system.

One way to bleed this out is to keep the banjo as low as possible while bleeding. Many times this is difficult because the reservoir is hard to keep level.

If that doesn't work, a power bleeder might do the trick. You don't need a lot of pressure, just a flow steady enough to force fluid past the trapped air.
 

·
Pale Rider
Joined
·
528 Posts
You could try a new, oil can, pump type. Fill it with brake fluid, attach it to the bleeder on the caliper, with a clean hose, pumping it full of fluid before you attach it to the wheel, to remove air. Pull the brake lever, on the handlebars about half way (secure it with a zip-tie to hold it in position), open the bleeder valve, and pump the 'oil can', to push fresh brake fluid up the line, into the reservoir. Monitor the reservoir, as it will fill up -- remove excess brake fluid before it overflows...

This method pushes fresh fluid up the line, which is the direction air bubbles want to naturally flow -- it helps push them up, and out of the system. Once you get the bubble out (watch for it to appear in the reservoir -- it helps to have an assistant), close the bleeder valve, top off the fluid in the reservoir, release the brake lever, and install the cover on the reservoir. Check the system properly, before riding, to ensure the brake works every time. I did not invent this method, I'm just re-posting it here. Cheers!
:coffee:
 

·
Premium Member
Joined
·
5,274 Posts
The trick I use is to tilt the MC so it is near 30-45 degrees, and just fill the reservoir enough to cover the tiny holes at the bottom; with some, less tilt is needed. Then, very slowly pull in the lever, say over about 5-10 seconds. When it is finally tight, let it pop back; the sudden return of fluid will pull some of the air out of the banjo and into the MC. Gently working the lever will expel this air out through those tiny holes. Then repeat the whole sequence, until you see no bubbles. Of course, brake fluid is a weak paint stripper, so cover everything. This works much faster with hydraulic clutches, because more fluid moves, but it will still, eventually, clear the banjo, without cracking the fitting and making a real mess.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #6
I agree there is air..but not sure how to use an oil can to force fluid up the system. It makes perfect sense but not sure how to do it. I try to keep the wheel to the left, because it makes the MC balanced as best as it could. I will try the snap back. (the whole bike is covered up to the forks). Thanks for the tip
 

·
Pale Rider
Joined
·
528 Posts
This is the type of oil can I am referring to: link. By pulling the brake lever half-way, and securing it with a zip-tie, forming a loop, the valve will be held open, allowing fluid to be pumped up the line.

With regards to using a hose, visit a pet center selling aquarium fish. Ask for the air hose, a clear plastic tubing. Take your oil can along, to ensure that the hose fits snugly over the can's tip. Buy around two feet of the hose. Push the hose on both the bleeder valve (open), and the oil can. You should be able to pump fresh brake fluid up the line, into the brake system, and the reservoir, atop the handlebars. Cheers!
:coffee:
 

·
Registered
Joined
·
5 Posts
Discussion Starter #8
Thanks for the link. I checked with the local home depot, but they said its an online only item..so I ordered one. Do I need to pump it into both bleeders or either one will work? I already have clear hoses of different sizes. Also, Heres a question..since i changed the MC, and rebuilding the caliper..why not new lines as well? Im looking at Galfer Steel Braided Lines. Any thoughts on this upgrade? **keep in mind, doing brakes are all new too me.
 

·
Member Map
Joined
·
23,911 Posts
Braided lines will often strengthen the braking power, since quality ones won't expand as much as stock rubber lines.
 

·
Pale Rider
Joined
·
528 Posts
Never seen two bleeders on one caliper, but I'm just a hack. Either one should work, but I would go with the furthest one from the reservoir, to try to maximize the flow path.

Steel braided lines will reduce, or eliminate, the hoses expanding when you apply the brakes. The OEM rubber hoses will expand, slightly, which decreases your braking pressure, slightly. Folks swear they can tell the improvement in braking, but I'm a bit skeptical -- it sounds too much like the laser-calibrated, butt dyno, to me. In a nutshell, steel-braided lines will increase the pressure on the calipers, when you pull the brake lever, increasing stopping power. If you have the cash, sure, go ahead, as the OEM lines are old, anyway. Cheers!
:coffee:
 

·
Member Map
Joined
·
23,911 Posts
Dual calipers will have two bleeders. Work from the one furthest away from the master. After the air is gone, squirt a little fluid through the closer bleeder to make sure no air worked it's way in.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #12
Yes, by 2 bleeders ..I meant one on each side. I dont have the oiler yet, but should have it by Friday. I played with the bike for a little while yesterday, but nothing I seem to do is working. I tried pullint the brake and snapping it back...and that "seemed" to work because the 2 or 3 times I did that, bubbles came into the MC. By the 4th time I did that, no more bubbles. I bled the system again, but same deal. It just wont get tight. If I pump the brake 2 or 3 times, it will stop the tire..but on open road, that wont cut it. When I got the bike, the calipers were frozen. I had to use a greese gun and pop the pistons out. The only thing I did was clean everything as best as I could..lightly sanded the pistons, and put it back together. I would assume that they are working because they do kick in after pumping the brake.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #13
My last option is too start over. Take the whole system apart. I already have a new MC. Im getting rid if the old rubber lines, replace it with steel braided lines, and complete rebuild of the calipers with new piston and caliper seals, and new bleeders. Brakes arent something to gamble on..so might as well do it right. As you stated, the OEM lines are old anyway, and it would take longer going through each line one by one to see if I have a bad line, then it would to just get all new lines. I have a spare set of calipers that I can start with. As long as I cover all the holes..can I paint the calipers? Its the least of my problems..but thought id ask
 
1 - 14 of 14 Posts
Top