Damaged brake pistons

Hello,

I decided to open the brakes of my KZ1000ST to clean them. It's a bike I bought some months ago, which I'm rebuilding.

Here's what the pistons looked like when I removed them:




And here is what I discovered after cleaning them:




I only drove 30km with that bike after buying it, and the brake did work. However, I think that kind of damage on the pistons could result in a leak, when the damaged part passes near the seals.

What's your opinion ? Would you replace the pistons ?

If a pit travels from one side of the seal to the other, it will carry a small amount of brake fluid. Otherwise it won't be a problem. I've often wondered if these pits could be filled with epoxy. Will have to give it a try one day.
-Duck

I agree with Duck. The seal is wide enough that it probably woudn't be a problem.

a friend did fill his with J B weld and sanded it smooth, it worked, I didnt think it would, far as I know hes still running it

I'll second the JB Weld. Maybe do what I call a scrape test with some brake fliud first. Smear some JB Weld onto a small piece of aluminum or something and let it cure. Then soak it in some brake fluid for a week or so, then pull it out and scrape it with a knife to see if the surface of the JB weld had gotten softer than the core.
Or, just smear some on, sand smooth, install and keep an eye on them. If they leak, you'll see it, but it's not like your brakes will just suddenly fail because of those pits.

I was thinking about this and forgot to say change it over to dot 5 , I have done it in mine and would never go back to dot 3.
yes its expensive, but, it dosent attract water, it will not eat the paint, has a higher boiling point

Apparently, I'm not the only one to have problem with the KZ brake pistons...



@BSKZ650: Are you sure you mean Dot5, and not Dot5.1? Dot5 can't be used in regular brakes. It eats the seals...

its the synthetic (sp) blue in color seems like it said dot 5 on the can, and is compatable with the rubber parts, you just have to make sure and clean out all the dot 3 stuff

I've had DOT5 in my brakes for over 20 years, 10 of them in storage. They were rebuilt at the time, with braided lines. After ten years of storeage, they worked well still. I did bleed with new DOT5 when I got her back on the road.
I just rebuilt my rear caliper and switched to DOT4 as I'm using an '04 GSXR master cylinder and resevoir. My piston looked very good for having been sitting in the DOT5 for over 20 years.

Post edited by: rstnick, at: 2007/05/15 14:30