Brake Caliper Piston Condition

[OldRider2]

Is there good rule of thumb as to how much rust/corrosion the piston can have and still use them? I realize new pistons would be the best but I would think that the outer edge of the piston could have some rust (cleaned up obviously) but still be serviceable.

[WingMan71]

Just rebuilt all three calipers on my '76 GL1000. So it's fresh in my mind.

Some rust/corrosion on the "outside" of the piston is OK. in this case "outside" means any portion that does not contact the seal inside the caliper bore when the piston is pushed all the way back in to the bore as far as it will go. You can measure the distance from the outside edge of the bore to the seal, and compare that to your piston. Anything in that range is OK to have some bad spots on.

Same thing for the extreme inside portion of the piston. There is a small section there that will never sweep across the seal either. Make similar measurements from the extreme back of the caliper bore to the inside edge of the seal. Compare that to the same section on the back (inside) portion of your piston. Slight problems there are OK as well.

Just remember, any portion of the piston that will sweep across the seal HAS to be clean and smooth with NO imperfections.

In case you need new pistons, Honda doesn't offer them anymore. But I found a company that machines new ones out of stainless steel. Beautiful work and I'm a retired ME, so I know good machine work when I see it. I used those pistons to rebuild my '76 GL1000 brakes just a week or so ago. They sell on eBay. Let me know if you need the source and I'll go back and look them up for you.

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[OldRider2]

When the calipers are rebuilt with new pads do the pistons fully seat in the bore or do they stick out a little?

[WingMan71]

When the calipers are rebuilt with new pads do the pistons fully seat in the bore or do they stick out a little?

They don't seat fully in the bore, but almost.

The large OD portion of the piston (the shoulder, you might call it) is, in fact, almost seated in the bore. The piston might move about 1/8" or so outward once installed with new pads and the brakes applied. Of course, as the pads wear, the piston will move out more to compensate.

The smaller OD outermost portion of the piston (the part that actually presses on the back of the pads) does stick out from the caliper bore almost completely. If it didn't, the dust boots would not fit on them.

My calipers are back on my bike now with the dust boots on, so I can't see to make a precise measurement for you.

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[Track T 2411]

Wingovations also sells the ss pistons for all the early wings... I've thought about trying a 'touch-up' using JBWeld, but I don't like to skimp on brakes (or tires). Do it right, do it once...

[OldRider2]

Thanks WingMan and Track T for the info. I kind of figured that the very outer edge of the piston if it didn't touch the seal could have some pitting in the piston. I realize new is better but my CFO keeps raising her eyebrows! I still have to paint the caliper (s) up and waiting for another one to rebuild. I was thinking this AM I could dry fit the pads and piston to see how far out the pistons stick. I don't normally skimp on brakes so if I need pistons I'll get them. I found several available last night when I was researching them.

[scootsx2]

Brake Crafters is also a good source for rebuild parts and kits.

https://brakecrafters.com/

[quadrunner]

+1 on brakecrafters, I bought all of my parts from him to rebuild all 3 of my calipers on my "83". Very friendly and knowligible.

[Old Fogey]

Stainless steel pistons for every model of Wing and for most other 70s-80s Hondas here:
http://www.wingovations.com/stainless-s ... 4588600239
(Yeah, even the PITA 82 Aspy)

[5speed]

big +1 for Old Fogey. bought my ss pistons from him. Great service..