Rear Brake Pistons Too Far Gone?

playfair

playfair

Joined
May 3, 2011
Messages
319
Location
Rochester, NY
Bike
2008 ST1300
STOC #
8441
Time to replace the rear pads, but upon inspecting the caliper I noticed a lot of rust on the pistons...
Must have happened that day I got stuck in a rogue "blizzard" :c(

Would love to be optomistic, but I'm doubting this can be cleaned up with just brake fluid and a toothbrush. Thoughts? TIA


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Hard to tell, I'd vet some brake fluid and a rag and see if that will rub off.
 
I'd venture to guess they are pitted. You could try to brush'em but I think removing them and polish them with some 600 or 1000 grit would be best however you get that far you may as well replace them.
 
By the looks of your (fairly new)brake pads, the pistons are prob most of the way in already and will only move out as the pads wear.

I'd clean it with some brake fluid and some fine wet/dry emery (wet with bf ), then clean off again with clean rag....

Then I'd RIDE.
 
Not sure I would use any abrasive stuff. I've heard of members using that and it messed up the pistons... the brake fluid and soft bristle toothbrush or just strips of rag may be enough to pull that stuff off, many times that surface stuff looks worse than it is... I think the pistons are pretty cheap and easy to replace if it ends up being the case.
 
What I see tho is the part of the piston thats always going to be exposed anyway... what is the pad down by 1/16 inch?
A good polish is going to be better than the rust particles. Like you said, if it don't work, replace.... not like it's going to instantly lose all the fluid.
 
Tom Mac 04a said:
What I see tho is the part of the piston thats always going to be exposed anyway... what is the pad down by 1/16 inch?
A good polish is going to be better than the rust particles. Like you said, if it don't work, replace.... not like it's going to instantly lose all the fluid.
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True. I don't think it would loose fluid but might stick some if what was used is too abrasive. However, ANYTHING is better than what it looks like now. Amazing how fast corrosion begins.. if I ride in the rain or wash the bike and put it in the garage the pad-to-disk area will start rusting in a day or two and leave a rust outline of the pad on the rotor.
 
I can see bad pitting. Time to get some new ones.
 
I used emery cloth to polish/clean the middle piston on my front right caliper because is was like yours. Doing so caused it to seat so tight with the seals that I could barely move it. I had a spare set of front calipers from a wrecked ST so I robbed a piston from one of them. I definitely would not sand them. As Mellow said, they are not that expensive, I would order a replacement.
 
JoeP said:
I used emery cloth to polish/clean the middle piston on my front right caliper because is was like yours. Doing so caused it to seat so tight with the seals that I could barely move it. I had a spare set of front calipers from a wrecked ST so I robbed a piston from one of them. I definitely would not sand them. As Mellow said, they are not that expensive, I would order a replacement.
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I was really trying to not use your name... LOL
 
I thought ya were, but thought I'd pipe in because, "I KNOW", I was there.

Assuming you have the ST1300, the outer pistons on the left front caliper are the same as the outer pistons on the rear caliper. I've got a set from the caliper off of a wrecked ST (2004 model). Check http://www.ronayers.com/ for your year model. If those will work, PM me your address. I'll drop em in the mail. That would leave you with only having to buy the inner one.

They are not as cheap as one would think. I believe they are around $22 each.

The p/n for the outer pistons (for the 2004 ST1300) are: 43207-MAJ-G41 Linky
 
3M 03130 Grit part number P320 from O'Reilly's Auto Parts.

I'm not sure why it's numbered that way, but having painted a few cars in my time, I'd say that it is closest to 1200 grit sandpaper that one would use to wet sand.

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Get yourself some green 3m scrubby pads, the longer the better. cut them in 1/4" strips or whatever width of the piston is showing. Moisten with brake fluid, thread the strip around each pad and saw away until shiny. Nice thing with the scrubby pads is you can pull pretty hard on them, they fit between the pistons, won't damage much of anything that's in there and it works with the calipers on the bike..
 
That makes me feel better... I would've use 800-1000 w/d wetted with brake fluid and was thinking there would be no problem

280 grit is kind of corse for metal and would leave marks/scratches
 
Green 3m scrubbies. Really. If they don't get it out, it's too far gone anyhow, at least for caliper pistons. If you start removing material, you're changing tolerances that were meant to be tight.
 
Hey, thanks forthe input guys!

JoeP, that is a wonderful offer, but the outer front and rear pistons are indeed different... Front are 22x35, and Rear are 22x39; 4mm longer.

Tom Mac, I measured the new rear pads at 5mm thick, and these have 2mm remaining. Guess they have a bit of life left?
Compared to the front, there's SO much of the piston exposed I started to panic, but this appears to be pretty normal. Not dragging or anything at this point.

Next wheel removal I will perform the "Mellow" restoration and take it from there.
 
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