KDXRIDER.NET

Team,
I was changing my front brake line yesterday and scratched the surface of the master cylinder where the brake line connects. It is a very tiny scratch but its enough to allow air into the brake / allow brake fluid out of the brake line. What are my options for repair?

See image below of similar master cylinder and an arrow showing where it is scratched.

Check the for sale part of the forum, I see a KDX being parted out...

I would try to sand it out. Maybe a drop of Bondo or JB Weld on a toothpick to try and fill and then sand. If you happen to have a Dremel maybe try one of the cone shaped polishing stones if its in a tight area. Easy for me to say sitting here on a laptop.

Take my master cylinder repair advice with a grain of salt, my repair might go something like this. Sand it down, reinstall it, still leaks, sand some more, still leaks, order a used one, rebuild it, won't pressurize, green 3M the bore, mess with it some more, and two weekends later it would be perfect.

Large flat file or replace the whole thing.

I think it needs a spotface tool on a milling machine to be plunged into that surface deep enough to remove the recess. I'd be too nervous to try to fix it with a hand tool. That face needs to be perpendicular to the threaded hole in order for the crush washers to seal tightly to the master cylinder and banjo bolt. If you took it to a machine shop and asked them to do it for you, it may end up costing more than buying a used master cylinder. But then again, we haven't seen said scratch, it may not even be that bad...a file may work if its minimal.

John_S wrote:I would try to sand it out. Maybe a drop of Bondo or JB Weld on a toothpick to try and fill and then sand....

Exactly how I repaired a rear master cylinder on one of my GSXRs. JB Weld fill, straight edge to scrape excess, let it cure and lightly sand. Hasn't had an issue in several years.

Make sure the area is very clean...place a small blob of jb weld over the scratch & refit new banjo bolt washers ...tighten down & leave overnight to dry.... Next top up with fluid & bleed....

You should be good to go.

I sanded the surface until the scratch was gone and annealed the old washers, filled with brake fluid and pumped the air out. The front brake works great now. It's had pressure for 12hrs and no leaks.

Don't reuse your old crush washers. First rule of brake banjo bolt removal. Repeat.

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Nice! Glad to hear ya got it sorted out. The scratch must have been smaller than I was thinking lol

ScruffyDroid wrote:Don't reuse your old crush washers. First rule of brake banjo bolt removal. Repeat.

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I annealed then reused them and they work fine. They have held pressure for 18 hours now. Should I be worried in the long run?

Tyl3r wrote:Nice! Glad to hear ya got it sorted out. The scratch must have been smaller than I was thinking lol

It was a tiny nick, just enough to catch a nail and let brake fluid out.

nice! and I'd probably take it for a ride down a long slope or something and stay on the brake before I called it good with the crush washers. I've reused them before...its worked sometimes, and other times they didn't.