Topic: Do I need to replace my caliper piston?

[The other Derek]

I cleaned the front caliper a couple of weeks ago and didn't think the piston looked too bad.  There are a few small pits though.  It looks like the edge is gouged also.  It may have gotten dropped at some point. 

Do you guys think I need a replacement?

[Kickstart]

I don't think that's too bad.  I would hit the gouges with some 1000 grit wet/dry to smooth down any proud edges, otherwise you may mess up your caliper when you try to reassemble it.

There was a recent post with someone asking the same question about pitting:
http://forums.sohc4.net/index.php?topic=111820

Theirs looked worse than yours.  I believe TwoTired said he could get away with filling those holes in with some Dow Silicone vacuum grease... so I suspect you could do the same if you were worried about it.

Personally, I would purchase a replacement stainless steel or a phenolic one... and then you never have to worry about it again.  But, I have definitely seen worse calipers... and road with a worse one for many years when I was younger. I think the pits in yours are small enough that it wont affect braking performance, but over time it will allow brakefluid to get on the outside of the chamber where it will continue to corrode your piston.

If you don't already have some, you should get some of this stuff... even if you don't use it to fill in the pits.  You should use it on the exposed part of the piston, between the piston and back of the brake pad, and between the brake pad metal and caliper housing:
http://www.google.com/search?q=DOW+CORNING+Silicone+-+High+Vacuum+Grease

I believe there's a brake rebuild FAQ on this site.. or just do a search on the forums... there is a lot of good information on the proper way to rebuild these brakes.

[Kickstart]

I was just looking at the picture of your caliper again... are the gouges on the side towards the brake pad or towards the caliper?

And same question for the pitting?  If the pitting is all the way in the caliper house (and not where the o-ring makes contact), then I would definitely say your piston is fine.

[Brantley]

Looks like the top of the photo points toward the pad, yes? Don't sweat the gouge, then. If that's the worst of the pitting I'd run it without worry, especially if you're reusing the old pads. New pads may push the pitting back to the seal area. Either way, I've run way worse than that. Get a new seal, keep a close eye on it, and budget for a new piston when the pads are due for replacing.

Dow Corning High Vacuum Grease is a bit spendy, but even a small bit will last you something resembling forever. It'll definitely help prevent the moisture that causes that pitting. Just mind you don't use it anywhere behind the seal, i.e. where brake fluid is.

[Shane72]

Don't let it slow you down at all.

I've taken a fine file to many worse than this, never a problem.  Seems to be a benefit of the flat and wide seal in the caliper that is very forgiving on slightly corroded pistons.

Just make sure there are no edges that catch a fingernail on the sealing/side surface.

All the best,

Shane

[shinyribs]

I've used worse with no issues at all.I think it's a pretty good looking piston IMO.I'd rock it for sure.

  If the pits really worry you ,you can fill them with epoxy and then smooth them out. Some will say no-no to that,but it works. I have a piston in a '48 Oldsmobile master cylinder that I epoxied yeeeeears ago. Still works fine.

[Teatimetim]

that is not a lot of pitting.  clean it up, as someone else said, 1000 grit to get any rough edges off.  You wont have a problem.

[The other Derek]

Thanks guys.  That's a little money that I can save for another project.