Topic: Front Brake Caliper Question - '78 CB550K

[bcollings]

When I got my '78 CB550k, the brake lever had no pressure and I could pull it back to the grips.  A quick brake bleed and I had more pressure, but then realized the piston was stuck and the brakes were locked on the rotor.  I just finished removing the piston from the caliper, where I found a tone of buildup and gunk, but I was wondering if it's necessary to replace the piston O-ring?  The bike only has 12k miles on it, and the O-ring looks like it's in decent shape with a little buildup around the edges. It's also worth noting that I've cleaned it all out with brake cleaner, so I'm not sure if that deteriorates the rubber enough to warrant a new O-ring.

Also, I was able to pump out the piston using the brake lever, so I think my master cylinder is in decent shape, but I think there's some buildup/residue in there.  Is it possible to just disassemble and clean the MC, then reassemble with the original parts? Or do I have to replace any gaskets or O-rings?

[Scott S]

 For less than $20, I would replace the O-ring in the caliper while you're already in there. How does the piston look? Any pitting?
 
 On the master, just make sure the tiny return hole is clear and not plugged first. These things and fresh fluid will make a world of difference.

[bcollings]

I examined the piston pretty closely, and it's in really good shape.  I'm going to try and get my hands on a new O-ring though.  I'll move forward with simply cleaning the MC, and hopefully be able to put it all back together without finding anything too battered.

[TwoTired]

I've reused the caliper seal many times.  Maybe as much as I've replaced them.  They worked fine for me.

Do make sure the groove in the caliper is spotless and smooth.  The deposits there aren't always dissolved by brake cleaner.  Piston retraction is performed by that seal (multifunction part).  So, it needs to have its original shape to do it's job and not be distorted by cystalized brake fluid lumps.

There is a caliper rebuild write up in the FAQ. FYI

[KennyRedman]

There is a caliper rebuild write up in the FAQ. FYI

Looked it up for myself too:

http://forums.sohc4.net/index.php?topic=259.msg207521#msg207521