Topic: Stupid leaking brake caliper.

[Scott S]

 CB500/550 front caliper.

 I salvaged a stuck caliper using the grease gun method. Cleaned everything thoroughly and reassemble.

 Leaked fluid around the piston.

 Replaced seal (from Z1, I think....). Still weeped.

 Bought new piston, even though the old piston had very, very tiny pits in a place that I didn't think mattered.

 Tried a different caliper body, even though I didn't see any obvious defects.

 Rode the bike this morning and there's fluid at the bottom of the caliper and on the fork. Looks like it's leaking when used now, but not when sitting.

 What next? Are there known problems with the seals from Z1? The piston certainly didn't fall in. I had to push it in past the seal.
 Also, sanity check: Does the solid side of the piston face the fluid or the pad?

[Scott S]

 Just ordered a genuine Honda seal from my local dealer....only $12.99

 Is there a measurement on the caliper body or anything? I made sure the groove where the seal goes is clean, lubed it with fluid during assembly, etc. Brakes firmed right up and bled properly, but I just can't get this thing to stop leaking past the seal/piston?

 And again, which way does the piston face?

[Bodi]

The solid side faces the cylinder. The end with the recessed "cap" faces the piston.
Cleaning the seal groove is A) absolutely vital and the most important part of reviving an old caliper B) really really difficult.
The best way I've found is with a dremel and a brass wire wheel. Stainless wire wheel is good as well but can remove a lot of aluminum. Brass/bronze is better. Plain steel is too aggressive and will leave steel inclusions on the alloy that will rust and cause endless trouble.
A dentist mirror is good to see inside the groove. You want no trace of white corrosion crud, clean bare alloy, and sharply defined corners on the groove bottom. Too much abrasion will destroy the groove but leaving any crud will interfere with sealing and the piston retraction on brake release - this is what stops the brake from continuing to drag when you release the lever.

[Scott S]

 Thanks. I'll double check the groove when I get the new seal, but I'm sure it was clean.

 There's a chance that I put the piston in backwards.....can't be 100% sure. If I did, would that cause a leak?

[MCRider]

Thanks. I'll double check the groove when I get the new seal, but I'm sure it was clean.

 There's a chance that I put the piston in backwards.....can't be 100% sure. If I did, would that cause a leak?

As mentioned the solid side goes to the fluid. Can't say if it "causes a leak" but you have to eliminate the variables.

[aperry]

If the piston is installed backwards then the pitting in the piston would be in a different position relative to the seal.  And if there's overlap between the seal and the pitting, then you might expect some fluid to escape.  Hard to say for sure though.

Aaron

[Bob Wessner]

A dentist mirror is good to see inside the groove. You want no trace of white corrosion crud, clean bare alloy, and sharply defined corners on the groove bottom.

I also used a dental pic, gently, to go around both sides of the circumference of the groove to insure the corners were clear and clean.

[Brantley]

A dentist mirror is good to see inside the groove. You want no trace of white corrosion crud, clean bare alloy, and sharply defined corners on the groove bottom.

I also used a dental pic, gently, to go around both sides of the circumference of the groove to insure the corners were clear and clean.

+1 to Drs. Bodi & Wessner. Open up and say "awww crap! Look at all the gunk I missed!"

[Scott S]

 Pulled the caliper AGAIN. Even though I may be doing it in a few days when the Honda seal gets here....

 The groove was clean, but I cleaned it again with a pick and a wire brush. It didn't look like there was much, if any, fluid around the pad or bottom of the caliper. I wonder if what I saw was just leftover from pulling and bleeding the brake yesterday? Maybe the wind blew it around?

 Anyway, the piston was backwards. The original piston was not. I remember think to myself, "Self, I think you're putting the new piston in backwards". And I did.

 That's all fixed, bled again, firm lever and working properly. I'll keep an eye out for leaks. I'm really wanting to debut this bike at a local Euro/Japanese/Cafe bike night tomorrow.