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Discussion Starter #1 (Edited)
Is this a lost cause?
In my effort to replace the pads on my single piston brake caliper, I decided to rebuild the master cylinder as well.

After purchasing the rebuild kits, draining the brake fluid, and disassembling the parts, I'm left with what appears to be very worn parts.
This is my first time doing brake work on a motorcycle. Is the caliper walls and piston too pitted to keep? Should I replace the whole master cylinder unit? Is there any way to clean these properly before the rebuild?

I've read some threads regarding online purchases. I think rebuilding the two will help my skills but if they're only going to fail after reassembly, I'd rather just buy new parts.
I don't feel like spending the money on new parts right now though. At least I have a second bike while this one is on reserve.
 

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I am no break expert, but judging from those pics it looks like a good clean (honing the cylinders) should clean that up nicely. I doubt that the micromilimeters worth of shavings the honing will create will effect the reliability of the piston - the power is in the hydrolics / pressure and not so much on how snug the piston sits in the cylinder.

IF you are going to go and buy new parts - keep an eye out for a better unit all together. Something off of a CB900 will boly on and is a much better break.
 

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Your parts look salvageable to me. Starting with the brake caliper, you can use a brake cylinder honing tool (available at any auto parts store for around $10) that chucks up in a drill. It's easy to use even if you've never done it before. You can also save $10 and simply sand out the caliper bore by hand using fine emery cloth. Clean out the seal groove as best you can and replace the seal. Do not reuse that 30+ year old seal! Clean your piston on a wire wheel or by hand with emery cloth. Wipe parts with a clean rag and then get ready to assemble.

It's often fussy getting the brake piston back into the caliper bore but be persistent. Lube bore and seal with brake fluid and bottom and sides of piston with brake fluid beforehand. A big c-clamp helps but only use it to get started. Once piston is started past the rubber seal, wipe off any excess brake fluid completely. You want only brake fluid on the inside and none on the outside. Put a very light coating of silicone grease on the exposed piston outside of the bore.

Fixing up the master cylinder is a similar principle; clean clean clean.
 

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Discussion Starter #4
I've read that one can accidentally sets the piston in too far. Is this correct? How far is too far?
 

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Discussion Starter #5
Update: Everything went together well. Flushed the brake line, scrubbed the rotor, and the rebuild looks like it's good to go.
I still need to break in the pads, but that won't be done until the remainder of my maintenance is complete.
 
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