GS850 Rusty piston cavity in front break calliper

[Guest]

Hi folks

My pistons are rusty so I'm replacing them.

But what about the cavity in which the piston sits? It's rusty too. How can this be treated? I've seen the overhaul guides on BikeCliff's site and they say if dirty or corroded then clean, but how?

Sandpaper and elbow grease?
Which sandpaper? More than one?
At which point can I stop sanding? Only once it's perfectly smooth, or is a little roughness ok? Define 'a little roughness' :-|

And how can I tell in advance if they are perhaps too far gone to salvage?

As always, many thanks to all for your responses
Assaf

[hampshirehog]

The corrosion in your caliper should come off with Scotchbrite pad - don't use anying rougher.

Stainless pistons on the rebuild? Problems sorted for ever then.

[Dogma]

Pits and gouges in the bore are fine, as long as there is no material raised about the surface to interfere with motion. There has to be enough of a clean bore to hold the piston too, around 80% cleanup or more. But if it's that bad, odds are the seal groove is also bad. The deepest part of the seal groove has to be smooth, and without pits forming a path for fluid to move through. Everything else is merely mechanical support for the piston.

[bwringer]

The caliper body is made of aluminum. It can't rust, so any rust you see is just left over from the rusted piston.

As noted above, clean it up with a Scotchbrite pad. Clean it up thoroughly afterwards to make sure all the abrasive particles are out.

[chuck hahn]

Replace the seals too and be 100% as sure as you can that the groove they set in is as clean as you can get it. Little wipe of fluid on the seals and pistons as you reassemble them.

[Assaf]

OK
Thanks

[Assaf]

Hi
I'm having trouble locating a US supplier for Stainless Steel pistons.
Any suggestions?
thanks
Assaf

[hampshirehog]

I don't know of any in the US but you could try Wemoto in the UK

http://www.wemoto.com/bikes/suzuki/gs_850_gt_gx/80-81/

or Nick Chambers on Ebay (he sells various sizes)

http://www.ebay.co.uk/itm/Suzuki-gsxr-gs-rear-caliper-pistons-Booted-type-/390450310234?pt=UK_Motorcycle_Parts&hash=item5ae8a6ec5a

If you buy stainless you don't need the boots (though you do have to clean brake dust off them when you fit new pads).