Topic: BRAKE BLEEDING PROBLEM

[CBXJOHN]

Hi guys, need some help.......I'm working on '76 CB 550, I keep getting a spongy brake handle. I've rebuilt the original master cylinder, re-bled the system, no difference. I picked up a clean used MC, rebuilt it, same thing. Is it possible there is air in stop light switch, or perhaps the switch is bad? I've done brakes on many stubborn to bleed bikes (like an '86 Magna) but this "simple" setup is giving me grief. Any advice or tips? Thanks, John

[Deltarider]

What I used to do was: remove the battery (or close the vent opening), remove the tank and lie down the bike on it's left side. After a couple of hours bring it back upright. Problem solved, because trapped air has made it to the reservoir.

[haill]

what I've had luck with is cracking the bolt at the brake lever/master cylinder after pumping the brake handle keep the brake handle pulled in to the bars and crack the bolt. wrap a rag around the bolt area to catch the brake fluid.
this gets the air trapped at the master out and seems to make a big improvement.

[Shoeboxjoe]

I'd have to ask how you're "bleeding" the brakes. I have a friend who's definition of "bleeding brakes" is to open the bleeder valve and pump the brake peddle/lever a bunch of times, then closes the valve! He also has spongy feeling brakes every time he "bleeds" his 

[flybox1]

got old or soft brake lines?
if one is bad, it wont mater how well you bleed them.

[CBXJOHN]

I'd have to ask how you're "bleeding" the brakes. I have a friend who's definition of "bleeding brakes" is to open the bleeder valve and pump the brake peddle/lever a bunch of times, then closes the valve! He also has spongy feeling brakes every time he "bleeds" his 

Good point, the bottom of the system, (the lines and caliper) have fluid. I install the MC, fill with fluid, and lightly cycle the handle until all the air rises into the reservoir. I hold pressure and crack the banjo at the MC to release any air in the fitting, then use the fitting on the caliper and bleed the lower part of the system. I also remove the caliper from the handlebar and tip it fitting down while cycling it to force any air in the banjo upwards. I also removed the caliper, pressure the pads out, and then force them in, reversing the flow of fluid up to the master. I'm up for ANY, AND ALL SUGGESTIONS, keep them coming! I'm just curious if air gets trapped in the stop light switch assembly. It's been decades since I've worked on one of these bikes, I'm sure I'm missing some trick.

Thanks, John

[CBXJOHN]

got old or soft brake lines?
if one is bad, it wont mater how well you bleed them.

That's a good point, but my '75 has original lines, and it's handle is tight.

John

[flybox1]

John,
in your first post, you had a"spongy" brake handle.
now you stated the handle is "tight".
relieve my confusion! please! 

got a side stand?
put your 550 on the side stand and crank your bars to the left.  this puts the MC up high.
tap on all sections of the brake lines and connections. and even hit the stoplight switch with a little heat(hairdryer/heatgun)  leave it overnight and see what comes up out of the MC in the AM.
if it is just a bubble, this might dislodge it. microbubbles cling, and dont like to go anywhere, but if heated and expanded, they might want to leave 

if still spongy, i'm at the end of my know-how.  new ss lines would certainly be a worthy upgrade.

[CBXJOHN]

John,
in your first post, you had a"spongy" brake handle.
now you stated the handle is "tight".
relieve my confusion! please! 

got a side stand?
put your 550 on the side stand and crank your bars to the left.  this puts the MC up high.
tap on all sections of the brake lines and connections. and even hit the stoplight switch with a little heat(hairdryer/heatgun)  leave it overnight and see what comes up out of the MC in the AM.
if it is just a bubble, this might dislodge it. microbubbles cling, and dont like to go anywhere, but if heated and expanded, they might want to leave 

if still spongy, i'm at the end of my know-how.  new ss lines would certainly be a worthy upgrade.

        Let me clarify this, first, the CB 550 is a customer bike that sat in a barn unused for 19 years. The brake fluid was a JELLY in the reservoir. I disassembled and installed new seals in the MC and caliper. The bore was good in the MC. The brake handle after bleeding feels mushy and sinks to the hand grip. My '75 CB 750 in comparison has original lines, and is "tight" by comparison. Meaning, even with original rubber lines, the brake lever will stop about a 1/2" to 3/4" away from the grip. I should be able to get the same action from the 550, so I'm sure I have air somewhere, but WHERE, is the question. I like the idea of the hair dryer, I will try that. That stop light switch, could it be bad? If it had a lot of movement inside it could create a feeling of excess air in the system. I may remove it this evening and swap it over with another, and I also have a spare set of lines.

John

[flybox1]

i think your switch is fine.
throw on your other set of (hopefully new) lines.
i'm guessing the original ones have gone soft on ya.