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Discussion Starter #1
Guys...

What was a quick flexi hose swap has turned into a full front brake overhaul? New braided flexi lines, disks and callapers etc... My question is should I replace the rear oil seals on the hub? They seem ok in place? Am I creating more work for no reason? I do have new spares?

Also advice on the piston please? Clean or replace?

Any advice?
 

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This is a "While you are there" task. I do not like doing things twice so while in there I would do full repair and replace all seals, bearings etc. Parts are cheap. Then you do not have to go back in and do it over cause of a leaky seal.

Remove the dust cover, clean it, use an abrasive cup paint remover in your drill and then paint and re-install.

You'll be glad you did.
 

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That slightly cruddy piston at the top can be polished nicely. You only need the cylinder surface to be smooth. The cruddy part is at the brake shoes - a little rust preventer wouldn't hurt if you keep it off the seal surface.

Nice job!

Robert
 

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Discussion Starter #12
Thanks.. The others are similar so I guess worth saving?

That slightly cruddy piston at the top can be polished nicely. You only need the cylinder surface to be smooth. The cruddy part is at the brake shoes - a little rust preventer wouldn't hurt if you keep it off the seal surface.

Nice job!

Robert
 

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That slightly cruddy piston at the top can be polished nicely. You only need the cylinder surface to be smooth.
Robert: That's true for drum brake cylinders, where the seal is on the od of the piston and contacts along the id of the cylinder. But disk brake calipers are the reverse: the seal is on the id of the cylinder and contacts along the od of the piston.

Therefore, the finish of a disk brake cylinder (aka "caliper") is irrelevant, as long as the groove for the seal is OK. The finish of the piston is what is critical.

Having said all that, the one piston shown in rooony's photo in post #2 doesn't look too bad. Assuming the other three aren't any worse, some light polishing should be sufficient. As you noted, the bad rust on the piston in his photo is on the area that the seals don't contact.
 

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I was referring to the photo of the piston, and meant the cylindrical surface - the OD of the piston as you said - needed to be smooth. Poor choice of words on my part. Your description was exactly what I meant.

Robert
 
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