Topic: Zero brake pressure on my '75 CB550.

[B. Alec]

Hey all, this is my first post;  I've searched the internet for an answer for awhile without much luck. 

I got a free 550 and there's absolutely no brake pressure on the front brake when I squeeze the lever. 

There is fluid in the line and the master cylinder, and when I removed the bleed screw completely and pumped the brake, fluid came out. 

I've tried to bleed the line per the manual(i.e., open the screw 1/2 turn, pull brake lever, close the screw, release brake lever) but no fluid comes up the bleeder hose I attached nor does the level in the cylinder change.  This is still the case after repeating the previous around 30 times.  Most of what I've read has made it seem like fluid starts to go into the hose right off, so I'm confused by this.

The lines themselves are a little bit cracked but there are no leaks anywhere, and I assume since with the bleed screw out pumping the brake did push some fluid out that the lines aren't the problem.

Is it just a matter of repeating this 100 times because there's that much air in the line or am I missing something?  I just don't want to be in the garage pumping away for an hour if it's not doing me any good. 

Reading the posts on this board has been soooo helpful for everything else I've done on the bike, so I'll take this opportunity to say thanks to everyone for that. 

Thanks,
Ben

[mgilvary]

You should have fluid coming out as soon as you start the bleeding procedure. The fact that you don't, but that you do get fluid movement if you remove the bleeder nipple, seems to indicate a clogged bleeder.

The fact that you get no pressure on the brakes at all suggests that the caliper piston is seized (probably due to the same gunk that's clogging the bleeder).

I'd suggest draining, dismantling and cleaning the entire brake system, then rebuild both the caliper and the master cylinder. I would also suggest new hoses. Sounds like yours are in bad shape.

There is a lot of info on this site about this procedure, and about how to remove a seized piston.

[Robert]

Don't look a gift horse in the mouth, look in the caliper.

[B. Alec]

Awesome, thanks guys.  While that's bad news, at least it's news.  I didn't want to go through everything if I didn't have to, but I guess It'll be good to learn the whole brake procedure top to bottom. I'll see what I can get done with this information and report back.  I'm waiting on throttle cables anyway. 

Thanks again,
Ben

[Bob Wessner]

When you get around to rebuilding the M/C, one of the seals has to be mounted ON the piston before you insert it. Guess how I know??

[B. Alec]

Yeah, I saw that!  No fun.  Now I'm having a helluva time getting the piston out, of course.  Actually, I'm having a helluva time just getting th brake line off the caliper.  That screw is welded on!  WD-40 is overmatched, as is my crescent wrench.

[TwoTired]

I got a free 550 and there's absolutely no brake pressure on the front brake when I squeeze the lever. 

Do you mean you get pressure on the lever but not at the brake disk?

Or, do you mean the lever bottoms out without achieving any resistance?

The former is a caliper issue.

The latter is either a bleed issue or a master cylinder issue.

Cheers,

[B. Alec]

The lever depresses fully without any resistance.  So a bleed issue it may be.  But, In taking apart the caliper to the point I can, it looks as if the piston might be a problem anyway; the pad on the piston is all corroded.   

If it's a bleed issue, are you suggesting that if I clean the bleed screw I might get fluid through the tube and be able to bleed the lines?   I can try that while I wait for the penetrating oil to get into the brake line connection on the caliper. 

Thanks!

Ben

[TwoTired]

Have you read?

http://sohc4.us/node/50

It is quite possible to bleed the brakes without using the bleed nipple at the caliper.  But, if the master cylinder is hosed...well...

[B. Alec]

Ah, how to know if the master cylinder is "hosed..." 

So I cleaned out the nipple(totally clogged, you were right), and tried to repeat the bleeding excercise.  I got some, but not much(maybe 6 inches or so), fluid in the hose, which quickly moved to the end of the hose that's in a brake-fluid-filled jar, leaving a big 6-8 inch space of air between the bleed nipple and the overflow jar. 

Thing is, the reservoir still doesn't change, leading me to believe that at least the hole from the cylinder to the reservoir is clogged. 

1. Is this possible while still having some pressure at the caliper end of the line? 

2. Is the next step to keep bleeding or to dissassemble the master cylinder? 

I did read that brake article, but it assumes the reservoir level changes. 

Still appreciating the great responses,
Ben

[Chris Liston]

To remove the piston it's best to have an air compressor,  put a folded towel on a work bench and the caliper piston facing down and insert an air hose from the compressor into the bleeder whole, blast away.  The piston should pop right out.

[TwoTired]

There are two holes at the bottom of the reservoir, If I remember correctly.  When bleeding, the tiny tiny hole makes most of the bubbles.  If that is blocked it won't let the air out of the system. Try sticking a wire strand from a lamp cord thru that tiny hole to clear it.

The master is hosed when it leaks or won't pump.   

I really don't like the air compressor method for caliper piston removal.  Too, many friends have been injured or have damaged something with the projectile from the caliper.  You have to have a master cylinder that works anyway.  Just use it to pump out the caliper piston.  It's non-explosive that way.  And, it flushes the lines while doing so.  And, there is a big difference in energy from 40 PSI to 175 PSI.  Yes, I know, it CAN be done safely.

When bleeding into a jar keep the open end under the fluid level of the jar, so the siphon isn't broken.

[hymodyne]

I screwed a grease gun into the first three or four lines of thread on my caliper and pushed the caliper out. took about 5 minutes to do and clean up.

hym

[Bob Wessner]

When bleeding into a jar keep the open end under the fluid level of the jar, so the siphon isn't broken.

Read a little trick in a cycle maintanence book once, use an empty squeezable ketchup bottle for the bleeding fluid. You feed the tubing through the little hole so it doesn't float/move around on you so much and when you are done, just snap the cap closed for the next time.

[78 k550]

use an empty squeezable ketchup bottle for the bleeding fluid. You feed the tubing through the little hole so it doesn't float/move around on you so much and when you are done, just snap the cap closed for the next time.

This is what I like about this site. All the little trick's.

[Robert]

>>>I really don't like the air compressor method for caliper piston removal

I use a manually driven air bycycle tire inflator to shoot the piston out of the caliper into a pillow.

An acquaintance once cooked the caliper. He filled the caliper with water, sealed the hole of the break hose with a screw and cooked it in the kitchen in a pot. The water vapor will build up an enormous pressure and shoot the piston thru pretty much everything. I actually DONT recommend to that. The moments when tinkering gets a lot more dangerous than riding

tinker safely 
Robert.