Topic: How do I refill my rebuilt front brake system?

[SWMN-CB500]

Seems like front brake problems are popular this week, so I'll add mine to the list. I just took apart the entire front brake and cleaned out a bunch of greasy stuff that was probably brake fluid at one time, and some rusty water.  I completely took apart the master cylinder and the caliper and everything in between and sprayed them with brake parts cleaner and compressed air, then put fresh brake fluid on all the seals and reassembled it all. Now I filled the reservoir on the master cylinder, but I can't get the fluid to the caliper. Anybody know any tricks or tips on filling a completely empty brake system? It's on a 71 CB500.

[ddrink]

Take your brake line where it would hook up to the caliper and put the end in your master resivor, and pull the brake lever repeatedly, until all the air is out of the line.  Hook the line back up the the caliper, and bleed out the caliper, using a speed bleeder, makes this part very easy.

[Flood]

Getting air out of the brake system is a major PITA on the old Hondas.
Just some ideas:

-use a BIG syringe with a long hose attached and fill the system from bottom to top using the bleeder nipple.

-when it's full, fix the brake lever lever with some elastic cord and let the bike stand on its sidestand overnight to get the last airbubbles out.

-don't work the brake lever too hard, you can blow a seal in the master cylinder (which I learned the hard way )

Cheers, Remi

[MikeDeB]

Not to contradict everybody but I've yet to have a problem bleeding these old systems.  I just did my K2 last week after rebuilding the master cylinder and caliper.  The secret is to prime the system.  One way is to attach a plastic tube to the bleeder screw and run the other end of the tube into some sort of catch tank.  With the resevior full and the bleeder screw cracked open, stroke the lever slowly until fluid appears in the tube.  The way I do it is to attach a Mity-Vac to the bleeder and suck the fluid through.

Once the system is primed close the bleeder.  Now stroke the lever quickly about 8 to 10 times and while holding it against the handlebar crack the bleeder screw.  Continue this until the lever becomes firm then stroke it quickly about 4 times and while holding pressure on the lever crack the bleeder screw.  Continue this until all the air is out of the system.  Also, don't let up on the lever at any time while you have the bleeder screw cracked open (you'll suck air back into the caliper).  With this method you should have the system completely bled in short order.

-don't work the brake lever too hard, you can blow a seal in the master cylinder (which I learned the hard way )

Was it a new seal?  I've never heard of this happening after a proper rebuild.

[Jonesy]

Once the system is primed close the bleeder.  Now stroke the lever quickly about 8 to 10 times and while holding it against the handlebar crack the bleeder screw.  Continue this until the lever becomes firm then stroke it quickly about 4 times and while holding pressure on the lever crack the bleeder screw.  Continue this until all the air is out of the system.  Also, don't let up on the lever at any time while you have the bleeder screw cracked open (you'll suck air back into the caliper).  With this method you should have the system completely bled in short order.

Put the cap back on the Master Cylinder when you do the quick 8-10 strokes on the brake lever, since the MC will sometimes spit brake fluid out through one of the tiny holes in the bottom- and the fluid that it spits out will always find the nicest-looking part of your original-finish gas tank.

[Flood]

-don't work the brake lever too hard, you can blow a seal in the master cylinder (which I learned the hard way )

Was it a new seal?  I've never heard of this happening after a proper rebuild.

No, you're right of course- it was an old MC.

[Bodi]

I'll just throw in my 2 cents worth.
I fill the caliper with brake fluid with the piston inserted just past the seal. This is easy with a syringe (I have an old steel veterinary type that works great) or with it dismounted hold it hoorizontal witha finger over the inlet and fill the cylinder then slip the piston in a bit. Remount it and connect the brake line. With a C-clamp or just your hands press the piston in. There's enough fluid in there to fill the lines and it will spurt out the bypass hole in the reservoir. Fill the reservoir and pump the piston out with the lever - not all the way or until the reservoir is empty!. Repeat the pressing in and pumping out until no more bubbles come out the bypass hole. Let it sit a few hours on the sidestand and repeat. Bleed any trapped bubbles from the caliper and it should be air free. Remount the caliper and pump the brake tight then fill the reservoir. Done.

[Dennis]

I'll just throw in my 2 cents worth.
I fill the caliper with brake fluid with the piston inserted just past the seal. This is easy with a syringe (I have an old steel veterinary type that works great) or with it dismounted hold it hoorizontal witha finger over the inlet and fill the cylinder then slip the piston in a bit. Remount it and connect the brake line. With a C-clamp or just your hands press the piston in. There's enough fluid in there to fill the lines and it will spurt out the bypass hole in the reservoir. Fill the reservoir and pump the piston out with the lever - not all the way or until the reservoir is empty!. Repeat the pressing in and pumping out until no more bubbles come out the bypass hole. Let it sit a few hours on the sidestand and repeat. Bleed any trapped bubbles from the caliper and it should be air free. Remount the caliper and pump the brake tight then fill the reservoir. Done.

Bodi,
That is really clever. I like that a  lot. As a matter of fact, I think that I will try that next time I have to do any brake work. Is this your original procedure of did you learn it somewhere else?

Harry,
How about putting this into the FAQ's?