So, I’m not entirely competent in hydraulic brakes, but after installing my Formula RX brakes and riding them once, they stood redundant for a few months (I know, I’m an occasional MTB’er).

Thing is, the rear brake pistons seem to have now clamped down on my rotor.

How so? I’m guessing I need a full bleed, but why has this happened?

Naaa, just sticky pistons. Take the rear wheel out and remove the pads. With a 10mm ring spanner (or large flat s.driver, use cloth as well) gently prize the pistons back and forth using the lever to push them out, and push them back in.

That should get you going…..

Failing that!, get rid and buy a set of Hope`s 😉

Hmmm, tried pushing the pistons back in, but not made much difference really. I’ll give it another go today.

I would remove a small amount of fluid,or re-bleed the system with new pads if worn, if none of the above works replace with hopes you can’t go wrong 😉

I think Formula are similar to Avid and I’ve had this problem with Avid (aka Avoid). I think it’s the fluid absorbing water and expanding, so as above, bleed off a bit of fluid and see if that helps.

As the fluid absorbs water the boiling point goes down, so overheating on long descents can boil it, resulting in brake fade, but if your brakes are new and you used new fluid (from a sealed bottle) it should be fine for a good while.

So much Hope love

If the avid and formula brakes both run a sealed system ( they do) how do they absorb water? Isn’t that like saying the new bottle if brake fluid you buy with a foil seal under the cap could absorb water?
Fwiw I have a set of hope brakes and a set of formula and avids!
Bought the avids from here when building a bike for my lad. For sale cheap as guess what the pistons won’t go back.
This is system over fill. Ie brakes bled when pads are worn then when the pads are replaced you can’t push the pistons all the back because there is insufficient volume in the reservoir for the fluid displaced from the calliper.

As mentioned above try opening the calliper bleed port slightly and pushing the pistons back. They will probably need re bleeding fully once you have done this. Not sure about formula but the avids need a bleed block fitting to keep the pistons fully retracted while bleeding( to prevent overfill)
But hey even hope brakes need bleeding sometimes.

Thanks for the advice. I didn’t get around to trying to remedy them today but i will probably just bleed the system.

The brakes have been ridden ONCE from new, along with the new pads. They were fine out on the trail and when I got home- just seem to have mysteriously gone weird while sat in the garage. Front brake is fine.

Hum-ho…

So they were ridden on the trail then left for months? Or weird after the ride?

I had a set of Avids lose all travel at the lever due to moisture ingress i’m guessing when not used over winter.

Just thinking of simple things, have you has the rear wheel off for any reason? Wondering if its not quite in the dropouts straight causing the pads to drag on one side of the rotor?