Rear Brake Won't Pump!

[mluk1]

I just took everything apart on my 1977 CB750F and am putting it all back together. I assembled the rear brakes just how they were when I took them off. I had new brake lines made and that was it. I'm trying to get the brake fluid to go through the system but it doesn't seem to want to flow into the lines. I am completely lost. I've bled brakes before, but is there a special procedure to filling the system back with brake fluid? Am I missing something? I unscrewed the nipple and started to push down on the pedal, with the reservoir filled with fluid and all I could feel was air coming out of the bleed hole. It doesn't seem to want to take the fluid. HELP!!!!

[TOOLS1]

It seems like you are just pumping with the bleeder unscrewed? If so it will never bleed. You must pump it up. Then while holding the pedal down. Loosen the bleeder. then re tighten it before releasing the pedal. You will need to do this several times. Another thing to do is tap on the lines, and fittings with a wrench. this will jar the air bubbles along.
If that does not do it. Another trick is to use an oil can that has a pump, and some small line. You fill the can with break fluid then connect the line from the can to the bleeder. this way you can pump the fluid in backwards. It's really a good method, because you are forcing the fluid, and air up.
Another way is to use a vacuum break bleeder.
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[mluk1]

I think I understanding it a little more now, I have to build up pressure right? So basically I have to do the same process as bleeding my brakes? Because nothing will happen if I just pump it because there is no pressure in the system. I might go out and buy a vacuum break bleeder, I got so frustrated last night trying to do this. I hope it's just the rear that is this difficult, I haven't even dealt with the front breaks yet!

[TOOLS1]

Those small master cylinders do not move much fluid. This makes them a lot of fun to bleed.
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[mluk1]

I would say that if that's the case then the $50 Vacuum pump will do, will it make it faster and easier? If so I would spend the money to keep my sanity!

[LukeM]

The basic bleeding procedure goes like this:

Assure you have enough fluid in the reservoir.
Attach a clear plastic hose to the bleed valve nipple, and put the other end in a can with some clean brake fluid in it.  This will assure that no air sneaks back in when you operate the bleed valve.
Open the bleed valve on the caliper about 1/4 to 1/2 turn.  1/4 worked well enough for me.
Press the pedal/lever about halfway, and observe what comes out of the tube. You should see some fluid, and maybe some air bubbles.  Clean fluid will eventually get there, and air bubbles need to go (leads to a spongy feeling brake).
HOLD THE PEDAL/LEVER STEADY, and then close the bleed valve.
Release the pedal/lever.
Check the fluid in the reservoir again.  Wait about 10 seconds or so.
Repeat until there are no more air bubbles coming out of the hose, then tighten the bleed valve.
Road test carefully, and repeat the process if needed.  If not, you're good to go.  

This may take a few tries before you get the hang of it.  You might also look around for a Youtube video on how to do this.

Good luck, and reply if you need more help.  I'm sure someone will chime in.
Luke M

[mluk1]

I have bled brakes before, numerous times. I guess my real question is: Is there a different method of refilling a break system then bleeding a brake system? I tried pumping the the fluid with the nipple tightened but it didn't seem to take anything at all. So I was a little lost.

[TOOLS1]

I have always used the oil can method I mentioned on new/rebuilt master cylinders. It is hard to get them going when they are dry.
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