Topic: 78 CB550 front brake problem

[tg305]

I recently disassembled the front caliper to my 78 CB550K because the front brake was dragging.  The piston was gummed up and the internals were nasty from sitting unmaintained for years from the previous owner.  The brake caliper was freed up and the bike rolls freely now. 


My problem is after bleeding the system with a bleeder pump, the front brake is very mushy and I don't have a good solid feel when I clamp down on the front brake.  Is this common for the older Hondas  or should I be looking at a master cylinder rebuild?  The pads are good with plenty of meat left on them.  It has a funky arm type setup on the back half of the caliper that may play in here but I for the life of me can't adjust it to make a significant difference....... 

tim

[SteveD CB500F]

Mushy feel is caused by air in the system. You need to keep bleeding. If they weren't mushy before, then this is the only reasonable cause.

Did you clean out the brake caliper (especially the square-section groove) and replace the square-section o-ring?

[Bob Wessner]

If it sat unmaintained for a number of years and you found the caliper in need of work, it would probably be a good idea to disassemble the master cylinder as well, clean it up and install a rebuild kit at that end as well. I agree, the feeling should not be spongy if bled correctly.

[tg305]

I'll give the bleeding another go.  I'm a bit confused about the square groove oring.  I'll disassemble and have a look.  I bled the darn thing till I passed almost a bottle of brake fluid through it.  But you're right it feels as if there is still air somewhere in there.  Don't know why.

[SteveD CB500F]

When you take the piston out of the brake cylinder, you will see the seal, seated in a groove within the cylinder.  This seal allows the piston to be drawn back into the cylinder when you let go of the lever, thus releasing the brake.  If it is dirty, old, hard (or all three), the piston will not withdraw and the brakes will bind.

[tg305]

that was the problem i was having before.  It operates pretty smoothly now.  the piston wouldn't retract after I applied pressure.  The brakes were mushy back then too.  Gotta be air in the line still. 

[SteveD CB500F]

OK - if they were mushy before, I'd recommend a Master Cylinder rebuild as well as checking your brake lines. The old black rubber ones "go soft" with age and can expand when you squeeze the lever, giving a mushy feel.  If you upgrade to braided lines, you will notice the difference - I went back to (new) rubber lines as I found the braided gave no "feel" at all - rock solid!

It's worth spending time and money on your brakes until you are completely satisfied - you've only got one life ...

[SCJIM]

here is what i posted on the old greenspun site...

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i speak from experience here so here goes... I've had to rebuild my front breaks completly. first: remove the calipers and pull out the pistons keep track of what parts came from what side. better yet do one side at a time. in the caliper theres a single rubber seal try to remove without dammaging it. or if it is already go get a caliper rebuild kit. you will need a cylinder hone to smooth off the inner walls of the caliper.
second: youll need to get some 1000/2000 grit emory cloth. lay emory cloth on a table and with a fiew drops of oil on it, rub the piston on the emory cloth until the surface is smooth all the way around. ""DO NOT JUST RUB IN ONE SPOT OF THE PISTON!"" keep rotating the piston to keep the sanding equal.

third: replace the inner seal into the caliper "new or old" and coat the piston and inside of the caliper with a little break fluid. press in the piston 3/4 of the way back into the caliper. next replace the boot cover to the piston and attach to caliper. now compress the caliper all the way

fourth: reassemble the calipers on the forks

fifth: ""BLEEDING"" attach a clear tube about 19 inches long to the bleeder nut on top of the 10mm wrench that you will need to open n close the nut with. "box end my pref." drop the other end of the tube into a jar or cup of break fluid. make sure the end is submerged in the fluid.

now fill the master cylinder and begin...

open nut, squeeze break, close nut, release break.

you will see the bubbles move slowly, but be patient.

repeat untill ALL you can see moving in the tube is fluid.

now do the other side the same way.

have fun.

Jim in South Carolina

[Kixx007]

I am a noob around here, and found this thread while searching for info about where to get a caliper rebuild kit.  Does anyone know of anyplace online to purchase this kit?! Its for a 78 550k.  My local dealer wasnt much help.

[SteveD CB500F]

Go to the General FAQ page for a longgggg list of online parts stores.

If you find any others, let me know and I'll update the list.

Steve

[Bob Wessner]

Kixx007,

What, within the caliper, are you looking to replace? Generally, there are the brake pads/pucks, piston and a piston seal. The piston seal can probably be had from a Honda dealer. There are sources for the pads and piston other than your dealer though.

[DBreaux]

I wouldn't recommend putting any kind of petroleum product, such as oil, into or onto internal brake parts.  The rubber used in many brake system will become soft and swell when they come in contact with any kind of petroleum products.  The brakes will start to feel spongy at first and finally just fail.  Use the proper brake fluid, i. e.  DOT 3, to soak, clean or lubricate internals in any brake system.  I speak from personal experience. 

Dwayne

[Kixx007]

Bob, All I need is the seal.  I think I found a place that can get me one.