Brake bleed - how hard can it be?

[sixinoz]

Took apart my front brakes for refurbishment. All back together, and having read all the threads here, what could go wrong?
I don't have a Mity Vac so filled up reservoir, attached pipe to bleeder screw and pulled lever. Bubbles appear in the container and before releasing the lever I closed off the bleeder screw. when I release the lever the fluid does not go down. Seems master cylinder will pump air but not fluid. Tried loosening top banjo bolt and pump the lever to prime it - all I get is air pressure. I have left the bike with bleeder screws open with the lever in different positions but no go. Both master cylinder holes are open so no problem there.
The bike is a 79 model but are seals and seal rods the same for all the Honda 5/8 inch master cylinders for that period? The new ones I put in are visually identical to the ones replaced.
Any help greatly appreciated as I thought this would be a routine job.

[Rick Pope]

Secure brake lever about 1/2 way back. A rubber band, electrical tape, zip tie, anything will work. Turn handlebars all the way to the left. Walk away for while. When you come back, gently "tickle" the lever. Did a rush of bubbles appear in the reservoir? Repeat as necessary.

[daves79x]

I think you need to 'bench bleed' your master cylinder first. Take the fitting off at the m/c. Fill the reservoir, then hold your thumb tightly over the port. Pump the lever a couple of times, then while holding pressure on the lever, slowly uncover a bit of the hole your thumb is on. Air/fluid should shoot out. Repeat until all the air is out and you just get fluid. Reattach your line, then try to bleed conventionally. If you can't get pressure in the bare m/c, then you have something assembled wrong with the piston, or the wrong rebuild parts. Honda 5/8 m/c kits are NOT all the same.

If you get this far, then do yourself a favor and follow my instructions you no doubt read about if you searched the forum. You do need a Mity-Vac to do it that way easily, but conventional bleeding will work. You may be a few days getting all the air out any other way. The CBX front brakes are the hardest to bleed in the universe.

Dave

[Larry Zimmer]

Just a thought --- Are you doing this with the cover assembled to the reservoir? If so, try it without the cover attached. Relative to what Rick described -- do it with the top lid removed from the reservoir. Once you have solid brakes, you can flush the possibly 'contaminated' fluid.

[hondaman160mph]

I agree with Dave, You do need a Mity-Vac to do it that way easily.
Cost of a Mity Vac $33.00
Efficiency of bleeding, not getting brake fluid anywhere, 10 minutes to bleed the brakes - Priceless

[Rick Pope]

I agree with Dave and Hondaman. My way works fine when you're messing around in the winter have plenty of time.

[sixinoz]

Thanks for all the tips and guidance. I tried everything so decided to strip the master cylinder again. Seals all fine and correctly installed. Thought I would just check the very small return port at the bottom of the reservoir. A very thin wire went through no problem. A slightly larger wire was no go. As I have another identical spare M/C I thought I would check the hole in that. Larger wire went through easily. So I went back to original M/C and reamed out the hole so that the larger wire went through.(I don't have a tiny .015? drill bit). Put it all back together and - Voila! - bubbles come up and I have pressure in no time.
Bottom line seems to be that the diameter of the hole is critical to getting bubbles of air through - too small and they won't go through under gravity or by working the lever. I think that a Mity Vac would overcome this problem as you are using pressure to draw the fluid through. Anyway all the tips for getting the final bits of air out worked a treat - thanks to all who replied.

[Larry Zimmer]

Good on ya, mate. Likely brake operation would not have been proper without that hole being proper size. So, all's well and better.