Topic: '76 CB550F front brake bleeding question

[jorwesflow]

I have already looked through countless threads on the matter, but I'm still having an issue (I think). I finally got this bike (my first one!) on the road yesterday. this being my first time on the road with a bike, I was having an out of body experience the whole time; it was surreal. except for a front brake issue... the caliper was not retracting properly and dragging almost the whole time. I know the risk of overheating the brake, but it wasn't too bad of a drag. just enough to squeak a bit and give just a little resistance, but not so much I couldn't walk the bike around if I wanted to.

I took the caliper apart, inspected the piston (it's fine, no pitting) and replaced the seal ring. one thing I did notice was the plastic ring between the piston and pad was not seated correctly in there, and got kinda mangled from the piston pressure (see pic). I had another one (what does it do by the way??)  so I replaced that, put it all back together, made sure the other side of the caliper had the proper clearance from the disc, and proceeded to bleed (re-bleed; I had already tried it a few times this week).

now that I'm bleeding the brake line again, I can't seem to stop getting small air bubbles to come out of both ends: at the bleed screw through the tubing attached to it which runs to a clear glass of brake fluid, and in the master cylinder reservoir through that tiny hole closer to the center of the bike. and I just kept pumping fluid through for an hour. (open bleed half turn + pull brake lever + close bleed screw + release lever + repeat + repeat + etc + lose mind + etc + refill reservoir)

is this normal to have small air bubbles coming out seemingly endlessly, and should I thus continue the bleeding process? or is there somewhere letting air in? is this a sign of a bad master cylinder? I haven't rebuilt it yet, because it seems to operate properly, although I have no idea what's going on inside of that thing. I don't see any leaks of brake fluid anywhere, but could air still be creeping in somewhere? am
I opening the bleed screw up too much? could air creep in through the
threads if I open it a half turn? trying to think of everything...

[burnoutking1971]

Hello
I have had the same issue with my CB 550 after I rebuilt the caliper with a stainless position and new seal. I replaced the bleeder screw with a new one and I replaced the hard steel line with a new one too. I found it was not seating perfectly. I had to  have my buddy help me with the process, you can do it yourself but it's easy to have a friend help you. I found that if I opened the bleeder and had my buddy press the brake lever hard it worked great. Also check the copper crush washers too. Sometimes they don't seal. Also I would recommend the stainless braided brake lines too to replace the rubber ones. They look cool and the front brake feels more firm too.

Also with a little riding the air should work its way out too. and the lever will feel better. I'm not an expert but just thought to share my experience.

[jorwesflow]

burnoutking, thanks for that info. I have heard the braided brake lines mentioned before. anyone have a link to where they're sold? what exactly are the copper crush washers?

anyone with additional ideas on my situation?

[mjstone]

http://forums.sohc4.net/index.php?topic=54790.0

Pampadori makes braided stainless brake lines.  If you use the code in his first post on his site, you get a discount.  Sometimes his site is down.  He does this when he is away, just keep checking back.  His lines are awesome, highly recommended.

MJ

[armour]

The master cylinder has 2 holes at the bottom. Your hole closest to the ignition switch may be clogged.
I JUST went through this . The fix ? An .84 cent #10 steel guitar string popped through the gunk , and
suddenly my disc released every time the brake lever was released !! This hole is tiny , a pin won't go
through it . 

[Bankerdanny]

I have to confess that I cleared mine (my res had nothing but some brake fluid jelly on one side when I got my bike) blowing compressed air through the cyclinder right at the bar. Cover your paint and wear eye protection if you do this.

[mjstone]

I forgot to say that pampadori sells the banjo bolts and copper crush washers as well.  The washers are what seals the joint between the banjo bolt and the fitting on the end of the line.  You should have 2 washers at each joint, one on top of the fitting and one on the bottom.  If you decide to replace the lines with braided stainless lines and keep the same setup as stock, it will be two lines, one from the master cylinder to the junction block and one from the junction block to the caliper, you would need 6 crush washers.  When I did mine it was part of a dual disk conversion so I needed one additional washer and a double banjo bolt.  Pampadori has all these parts and even makes single lines so you can eliminate the junction, but you loose front brake light switch.  He also sells a special banjo bolt that includes a brake light switch to solve this problem.

MJ

[jorwesflow]

thanks for the help!

this might be a stupid question: I understand what causes the piston to retract back into caliper, but what sticks to the pad itself to keep it attached to the caliper to draw it back? ie; what keeps the pad from separating from the piston when it retracts?

[jorwesflow]

ok seriously y'all please help
me figure this out. I have pumped over a quart of brake fluid through the line. and I'm still getting tiny bubbles at both ends. there's no brake fluid leaking anywhere, but can air leak into the line somewhere where fluid can't leak out? the two
holes in the reservoir are working fine. I am stumped!

I don't know if you can see the tiny air bubbles at the bleed valve, but they're there. :/

[Bankerdanny]

Those could just be leaking in from the tube itself, they aren't necessarily coming from the bleeder.

How is your lever pressure? Don't obsess over the bubbles you are seeing. Ride your bike for a while, do you have to pump the lever to get decent braking force? If you pull and hold does it start to go down?

[Toxic]

Those could just be leaking in from the tube itself, they aren't necessarily coming from the bleeder.

How is your lever pressure? Don't obsess over the bubbles you are seeing. Ride your bike for a while, do you have to pump the lever to get decent braking force? If you pull and hold does it start to go down?

This happened to me, I didn't realize the little bubbles I kept seeing were not coming from the bleeder but from around the clear hose.  As mentioned above how does the lever feel?  If you pull on it and it continues to go down, that ain't good.   What helped mine was I zip tied the lever tight to the handle bar and left it overnight.  The little air bubbles that were left in there made their way to the top.  The difference in brake feel was huge

[jorwesflow]

ok, thanks fellas. I won't obsess, but I'll keep my eye on it. I actually already did zip tie the lever down for 24 hours, came back, started bleeding the line again, and I couldnt believe the amount of bubbles I was seeing come out of the bleeder screw. for that 24 hours, I left the bleed screw open (half a turn) with the lever zip tied. should I have kept it shut? also, can anyone answer what I asked earlier? -->

this might be a stupid question: I understand what causes the piston to retract back into caliper, but what sticks to the pad itself to keep it attached to the caliper to draw it back? ie; what keeps the pad from separating from the piston when it retracts?

[armour]

Does the brake grab still ?
Did you try the guitar string ?
Lean the bar left so the master cyl is highest ( overnight ).
Did you rebuild the master / caliper ?
Did you replace that bent/warped plastic ring ?
I also bought a mity vac , which when pumped to suck the fluid thru the bleeder , finally worked best .
It took me days to figure all this out, along with reading a ton of threads . The manual sucks for true instructions.
I rebuilt everything and started out with a dry , NO FLUID scenario .
Please post what eventually worked for you and why . We like real , actual solutions !

[jorwesflow]

Does the brake grab still ?

yes, but it's not letting go. brake drags like crazy. I can push the caliper against the disc with moderate force to get the piston to retract back into the caliper.

Did you try the guitar string ?

no I haven't. the little tiny hole in the reservoir seems to be working. fluid squirts up when I first squeeze the lever.

Lean the bar left so the master cyl is highest ( overnight ).

I did that...

Did you rebuild the master / caliper ?

not the master cylinder yet, because I was fairly certain it was operating well. now I'm having my doubts. I did partially rebuild the caliper. new seal ring for the piston, piston was in good
shape with no pits. maybe I need a new bleed screw?

Did you replace that bent/warped plastic ring ?

yes I put one from another caliper in there. not new, but definitely structurally in tact.

I also bought a mity vac , which when pumped to suck the fluid thru the bleeder , finally worked best.

i might pick one up...

[armour]

There are 2 (TWO) holes in the bottom of the master cylinder reservoir .
The one that needs cleaned or unclogged won't be the one that squirts . That's the bigger of the two.
You will just remove cap, get that steel guitar string end, and gently push it through the tiny hole. You keep the fluid in and topped up the whole time you bleed , yes ?
Sounds like you may need to fully rebuild your master cylinder if the above doesn't work ! 

[jorwesflow]

There are 2 (TWO) holes in the bottom of the master cylinder reservoir .
The one that needs cleaned or unclogged won't be the one that squirts .

well in my MC res, it's the tiny hole that squirts up fluid, not the larger one. maybe that's a bad sign?

You keep the fluid in and topped up the whole time you bleed , yes ?

absolutely yes.

Sounds like you may need to fully rebuild your master cylinder if the above doesn't work ! 

yeah I'm about to order a kit. what special tools do I need to do
it? I watched the video in the trick/tips section, and he said something about a piston pulling pliers or something. I don't think
I have that. is that a special
order kind of thing? Any other tools I need to rebuild the MC?

once thats done, I'll move towards the braided lines if things aren't working right still.

[jorwesflow]

can anyone answer what I asked earlier? (see below)

this might be a stupid question: I understand what causes the piston to retract back into caliper, but what sticks to the pad itself to keep it attached to the caliper to draw it back? ie; what keeps the pad from separating from the piston when it retracts?

[vrenlos]

can anyone answer what I asked earlier? (see below)

this might be a stupid question: I understand what causes the piston to retract back into caliper, but what sticks to the pad itself to keep it attached to the caliper to draw it back? ie; what keeps the pad from separating from the piston when it retracts?

When the caliper is assembled back onto the bike, there is no possible way for the pad to fall out - it basically just sits in there.  As for retracting, the rubber seal inside the caliper body pulls back the piston and allows the pad to pull back, albeit only a few thousandths of an inch.  This is enough (with a rotor in decent shape).

My two cents - rebuild and/or replace the MC.  I thought mine was ok, and I could bleed the system to operating pretty well but it would allow air in and every few days I'd be stuck with a smushy brake and pulling at next to nothing on the lever.  I actually retro'd a harley 7/16" front MC (14.2mm vs our stock 14mm) and it seems to be working well.  I also have Pampadoori's braided lines, and they are pretty great, though I had to drill out one of the fittings to take the harley banjo.

[Jon]

I wouldn't put a kit in the master cylinder yet.

When bleeding try;
Bleed nipple closed
Pump brakes 4-5 times quickly & hold
Crack bleed nipple to release fluid then refurbish bleed nipple
Repeat


Leave it overnight with the brake lever in and bleed nipple closed.

Brakes will always drag some when bleeding & spinning wheel by hand, have you set the stopper adjustment on the caliper hinge?

[jorwesflow]

As for retracting, the rubber seal inside the caliper body pulls back the piston and allows the pad to pull back, albeit only a few thousandths of an inch.

I get that, I mean I pulled the caliper apart and rebuilt so I pretty much understand it. but when the piston retracts, I just don't get what keeps the pad and piston from separating enough to where that nylon ring in there could drop down from where it's supposed to be seated. that's what seemed to happened to me already which messed up the first nylon ring I had. it dropped
down a bit and the piston was crushing it off-center, which warped it. I'm just trying to understand how this stuff works.

[jorwesflow]

Leave it overnight with the brake lever in and bleed nipple closed.

ok, I left it for 24 hours with brake lever in and bleed open a half turn, which maybe let air in through the threads.

Have you set the stopper adjustment on the caliper hinge?

yes I set that as close to spec as possible (.1" or something I don't remember)

[Bankerdanny]

The ring itself creates the small vacuum seal that allows the piston to pull the pad back slightly as it retracts. If your old ring had hardened or been damaged, or if the piston face or back of the pad was corroded and it couldn't seal, that could account for the failure to retract.

[TwoTired]

I guess you haven't read the Brake FAQ.  There is a caliper rebuild walk through there.

In it, it explains the use of dow corning vacuum grease to coat all metal parts behind the friction pad.
Water can still get in but the silicone grease just sheds it, preventing corrosion damage to caliper piston, friction pad backing.

The grease is rather sticky and holds the nylon ring in place easily.

The brake arm spring retracts the fixed pad .006 inch.  The square section seal in the caliper pulls the piston back.  Grease adhesion keeps the pad in contact with ring and piston.  And, any contact with the rotor would just knock the pad back into the caliper bore.  You should have dry assembled the piston and pad into the caliper without the seal to ensure both can move freely in the caliper bore.
Also, the seal groove should be cleaned thoroughly while using an inspection mirror.  Distorting the seal shape with crusty bits or piston corrosion pits, hinder the seal retraction capability.

The stock brake system can be bled without ever cracking the caliper bleeder.  In stock form, the master cylinder bleed hole is the high point of the fluid system and all the air will seek the highest point.  The low bar/clubman type master cylinder mounting often prevents the master cylinder relief hole from being the high point, and makes bleeding the system problematic.  The stock system/arrangement will bleed itself overnight.

Rubber lines fatigue with flexure and it also loses its shape memory over time.
Ever stretched a brand new rubber band?  The first stretch was the hardest, right?   Subsequent stretching was easier.  Same thing happens to rubber lines, even though they have braided fibers embedded.  Even if the brake lines expand just a little, it consumes more volume from master to fill it, and higher pressures just stretch it more.  This pressure is therefore diverted from the friction pad to rotor pressure.

Being the first production disk brakes on a motorcycle, the lever function was designed to mimic a drum brake, and NOT allow the front tire to be locked.  Newer bikes with far more tire contact can have a stronger braking system, and people have been trained to use it without locking up the front tire.  Trust me, you don't want to lock up the front tire.

The stock system components with SS lines will allow you to squall the front tire, if you use your whole hand to apply pressure to the lever.

Cheers,

[armour]

The only special tool needed would be the circlip pliers , 45 degree long nose .
I used the straight kind but I had to grind the halves to fit - don't do this. Also , use factory parts to rebuild the master.

You may be right on the squirting ''tiny'' pressure relief , mine was clogged and never squirted.
I am sold on the stainless, braided hoses after reading the elastic band comparison though .

I also bought the stainless piston for 35 bucks off ebay . Perfect fit , made in Germany and half the price of factory !
I'm also using DOT 3+4 fluid ( one bottle ). I haven't replace the bleeder yet, and I've noticed slight seeping .

I think the mity vac ( 38 bucks on sale at Lordco here ) really worked for me , and it will for you too.

[bryanj]

Have you de-seized the pivot pin on the caliper bracket?