- Formula Oro piston replacement problems
I’ve just tried replacing the pistons and piston seals in an old set of Formula Oro callipers as the pistons were seized. Getting the pistons out wasn’t a problem (track pump attached to bleed valve) although required a lot of pressure. However, fitting the new pistons and seals has proved problematic. I can’t find any instructions on the web so maybe someone on here can tell me where I’m going wrong.
Covered seals in light coating of supplied grease.
Pushed seals into seat, making sure not twisted.
Pushed pistons into place one at a time by using old brake pads and levering with a screwdriver – took a bit of effort but the eventually clicked in place.
Went to bleed brakes but when applying pressure with the syringes brake fluid leaked out of pistons.
When I took the calipers apart again i found that both the new piston seals were badly damaged.
I’m obviously doing something wrong, I just can’t see what. Any suggestions would be greatly appreciated.Posted 4 years agoNorthwindSubscriber
The amount of force needed to fit the pistons isn’t right- they should go in with almost no force, so that’s where the damage has happened. But I don’t know why it was so hard- is it possible the seal channels are corroded? That could push the seals out… (fairly common with motorbike brakes, you don’t see it often on pushbikes but then if they’re early Oros they could be pretty old.
Maybe a more helpful contribution- I’ve got a silver Oro caliper somewhere which you can have, if I can find the sod.Posted 4 years agooink1Subscriber
Having rebuilt more hydraulic calipers than I care to remember, I have to say that Northwind is correct. You should be able to push the piston back into the housing with fingers alone – the fact you couldnt suggests the seals were sitting proud and were mashed by the piston as you pushed it back. Get a small right angled pick and run it around where the seal sits (Top and bottom if that makes sense) to remove any corrosion and then clean out with brake cleaner, fit new seal and try again 🙂Posted 4 years agoNorthwindSubscriber
Ah, not much, it’s the leftovers of a brake I raided for spares. Will hopefully be able to root it out at the weekend
(Oros are still excellent brakes and competitive with the new stuff but tbf it’s not usually worth spending a lot on maintaining them, you can buy good condition sets for a ridiculously small amount. )Posted 4 years ago
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