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My mate has just picked up a Kona Dawg Deluxe from the classifieds. The bike is mint, bar the fact it's stood for a while. The front brakes are good, but the back brake is sticking. Having had a closer inspection there is signs of corrosion/rust on the inner caliper around the piston.
I've seen that hayes has replacement pistons quite cheap. Are they an easy replacement or are they difficult to do?
Very easy to do. Undo two bolts to split the calliper. The only challenge is getting the old pistons out. If you've got an air line that's easy. If not I guess brute force is fine as you're chucking them away. The new ones just push in.
Is there any chance the caliper body is damaged with corrosion or not?
Is there any chance the caliper body is damaged with corrosion or not
Possible but unlikely to cause major problems.
They use a phenolic composite piston in the HFX9's & alloy caliper, the pistons tend to wear a groove where they sit around the seal, causing them to either stick or start leaking.
You can almost pump the pistons out before the split the caliper (makes life easier to remove)
Fit new seals & pistons, rebleed & job done.
If the new pistons don't sort it then CRC were doing old style oem Hayes nines very cheap - £35 or so IIRC. Can't get on the website at the mo to see if they're still there - if so it's an easy replacement if the brake is knackered.