FREAKING CALIPERS!!!

[raygreenwood]

The hone marks will not be a huge issue on performance of the part per-se...but they will be a wear issue on the piston. Again, that is not a problem with braking. But, many of these pistons are plated. The faster you wear marks in the plating...the faster they pit. What this really causes on the calipers...is friction. Its no big deal on teh pressure strok...but can be a big deal on how smoothly it retracts. The best way to polish caliper walls...and master cylinder walls for that matter is with a stick or dowel...with a slot in the end. Slip in several assymmetrical strips of 800 grit first...and roll it around the stick to the diameter of the bore...then turn opposite the wrapping. You are essentially making a fine grit hand flap wheel. Use some brake fluid. use no ower tools...and no compounds. You want to remove as little metal as possible....since you will not be getting oversized pistons. Then move on to 1000-1500 grit. Finish with 2000. You could just use 1000 and 2000. They will polish to almost a mirror smooth surface. Use a wrap of this on the piston...and finish with the finest steel wool.
I use the finest grit 3 puck hone I can find to de-rust. Very slow....no up and down...or not very much. Just trying to get the rust if any out.
These bores do not wear crooked...so just a slight surfacing. Then polish.
Remenber...that all of the force is applied against the piston. It has no rings....so an excess gap causes potential blow-by. Now...that being said....the seal acts much like a stdard piston ring. The fluid that bypasses the piston gets under the bottom land of the seal...and compresses it. That forces it outward...and inward at the same time, sealing the ring bore and against thpiston. The farther distance/area this seal has to expand...the more prone to leakage.
Also,.....it is the distortion of this seal...that primarily helps to return the pistons to its bore. Unlike the rer brake shoes...there are no springs.
Unless its downright oversized..it rarely leaks....but what it causes is that semi-sticky caliper piston that always seems to be just barely in contact with the rotor. Quite annoying.

Its no big deal if you have honed them already. Just split them again...and lap them smooth. If careful...you can probably get three rebuildings or more. Ray

[DeathBus]

Aaaaaaagh....do not tooth up the caliper walls. They must be smooth as a babys a*s. These do not have piston rings to break in. Although it won't hurt anything, the ttooth burnishes the piston. The piston rubs on the seals. Also, rough sides collect micro water bubbles. These should be polished unil smooth with like 1000 grit or better. Same goes.....especially...for a brake or clutch master cylinder. The hone marks on the walls....must be lapped out as they wear away at the seals. Ray

Yes they were smoother when I was done with the emery cloth.