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Disc caliper leaking past pistons


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Is trials this hard on your rear brake caliper piston seals? I'd been running some Magura MT5 calipers for a year or two, and in the end they tended to slowly get a bit wet around the pistons. The pads occassionally got contaminated and needed to be cleaned/replaced, after which is was generally fine again for a good while. Had had this before: years ago I tried some Formula T1 brakes for trials, two sets actually, which both started to blast oil past the pistons immediately on their first ride.

Anway, I replaced the Magura's with some Hope Tech3 V4 brakes I still had in a box from my downhill bike, and they worked great for a month or two. However after not having used the bike for a few weeks, I just found out one of the piston seals of the rear brake has crapped out massively. One of the pistons is covered in black junk, as is the pad. Of course, and frustratingly so, after cleaning up and clamping the brakes on hard for a while on a bleed block, they remain dry. So I reckon replacing the seal won't make any difference. This was the same with the Formula brakes, replaced the seals, still spewed oil on the first back hop, while they still worked fine and didn't leak on a regular mountain bike.

So is this a common occurrence with disc brakes being abused for trials? Or perhaps maybe something to do with the plastic phenolic pistons used on these brakes and their tolerances/finishing quality? (I've always wondered why Hope equips their Trial Zone with aluminium pistons)

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