CB550F brakes will not bleed

[NickMcDonald]

Hi all. Im having a nightmare bleeding the front brakes on my 1977 Honda CB550. I fit new sintered pads, a new cast iron rotor, and I rebuilt the master cylinder. Now the brakes won't bleed. I tried the traditional bleed method with no success. I have tried pumping the fluid into the caliper bleed nipple in an attempt to reverse bleed up and out the master cylinder reservoir. I have tried wiring the brake lever shut and letting the reservoir bleed itself out over night.....and I'm still not having any luck. I have got a bit of pressure....squeezing the brake lever into the twist throttle stops the bike when going about 20kmh.....but that won't suffice at open road speeds...or even 50kmh. Someone suggested clamping the brake lines with a vice grip, and then pumping the brake lever. If the brake lever goes hard, which it did, its supposed to suggest the problem is with the caliper end and not the master cylinder end. Either way, the brake lever is still spongey! Any suggestions would be much appreciated. Failing that, does anyone know of a brake guru based in Auckland? Cheers.

[ellipsis]

...had this nightmare...it ended up being the sleeve the piston in the m/c ran in , was pitted and not holding pressure...worth a look...cost less than 30 bucks to get it resleeved...

[skippa1]

Not sure if I would be clamping brake lines with vice grips.....

[Tazz]

...had this nightmare...it ended up being the sleeve the piston in the m/c ran in , was pitted and not holding pressure...worth a look...cost less than 30 bucks to get it resleeved...

Same can happen to the caliper piston. You've already overhauled the m/c and thrown a new disc on, might as well grab a caliper kit and go to town on that too.

[NickMcDonald]

Haha yeah, made sure I only did it just enough to give them a gentle squeeze. And ellipsis, was it quite visibly pitted? I had a look and it didn't appear to be marked at all, so I left it alone. The frustrating thing is, I had perfect brake pressure before. The reason behind me changing to the sintered pads and cast iron rotor was that the factory gear squeals horrendously.

[NickMcDonald]

Worth doing the caliper to? Didn't look pitted, but yeah I may just got ahead and do the whole lot anyhow. Cheers.

[Tazz]

At the very least just pull it apart and do some MkI eyeball analysis then throw new seals in and hammer it back together depending what you find.

You'll need to look closely (as in more than a glance). Air doesn't need much of a gap...

[ellipsis]

...it felt pitted more than was visible...but it was obvious that the surface was compromised...

[imdying]

Don't worry about pitting in regards to bleeding; it will either leak, or it will not.

If clamping the line gives you a lever, then the master is fine, the system is just not bled.

Don't clamp the lines with vice grips, it can damage the hose. Use a brake line clamp, they're freely available and cheap.

Short stroke the master rapidly to ensure the pistons are all the way out. You only require a small build up of pressure to accomplish this, and from your description you have sufficient.

Worst case, consider hanging the calipers above the master when bleeding it.

Make sure the calipers have their bleeders at the highest point. I have seen setups where people have transposed the left and right caliper, putting the bleeder at the lowest point.

Don't worry about vac/pressure bleeding, I've yet to find anything that won't bleed with the end of the hose submerged in fluid.

[HenryDorsetCase]

Welcome to the wonderful world of SOHC Honda front brakes. Guess what? Even when they work they are shit compared to modern brakes. Yours will be the swinging caliper with the fixed rear pad I take it? same as my CB400F. 550F's still only have one disc too IIRC.

The fact that you can clamp the hose suggests it might be original? If so remove it and throw it as hard as you can away from you. My recollection of those is that there is a fixed metal part that is clamped to a fabric covered rubber hose. Awful thing. I ended up with a steel braided line from caliper to M/C in one piece.

You need to take it all apart and start again. You have rebuilt the MC: great. does the fluid return hole work? all the seals present and correct? then check the piston as Mr Ellipsis said.

those calipers only go together one way and the bleeder is at the top. once you have sorted out a hose from mc to caliper then its time to check the caliper piston and seal and such. you might find that it wont bleed because the caliper won't swing. or the piston is locked in the bore.

or something. I would offer to copy the relevant pages of the Hanes manual but dont have access to it at present. Have fun.

edit. If you want to sell the bike, I'd be interested.

[NickMcDonald]

Ahh some good info here guys, thanks! I'll get back into the garage and have another go. And Henry, I have considered selling it, among other things including burning it, pushing it off a cliff etc....but I'm determined to sort this brake issue and get back to riding it! I'll let you know how it goes and what the issue was. Cheers.

[Devil]

Worst case, consider hanging the calipers above the master when bleeding it.

Make sure the calipers have their bleeders at the highest point. I have seen setups where people have transposed the left and right caliper, putting the bleeder at the lowest point.
Along these lines, before taking the whole lot off, just take the caliper off, and turn it to get the nipple up, then bleed. Then turn it over further, then bleed again.

The rear brake caliper on my aprilia is a bit of a dick like this and has to be 'burped' in a couple of different positions otherwise it just will not bleed.