Formula RX brakes, piston not returning

I’ve had the brakes from new for the last 7 months, and when it came to replacing the pads the pistons would not return unless I opened the bleed valve on the resevoir.

I didn’t bleed them as they felt fine afterwards, but I’ve just replaced the pads again and the same has happened.

Is this something a full bleed should fix, or should I be sending this back under warranty?

Do you mean you couldn’t get the pistons to push back to allow you to get the pads on the rotor ? e.g when you push them back they come back out ?

Yeah, usually I would just push them out with the old pads in using a butter knife, but these pistons hardly budge at all.

that’s how it is mate, they’re a fully sealed system… dunno why you’d expect anything else really ?

So you have to let fluid out everytime you change the pads, and re-bleed them?

weeksy, Im afraid you’re wrong on this one.

I wouldnt expect to have to let fluid out just to get the pads in on a properly functioning brake. Otherwise you’d have no fluid left in them after a couple of pad changes.

Formula’s instructions also state you just need gently press the pistons back in prior to fitting the new pads.

I have the same brakes and they are a pain in the arse when its time to change pads. I managed to get the pistons back in far enough to get the the wheel back on. Now i have barely any movement in the lever and they are dragging slightly.

Yin,

I may be wrong in theory, but my experiences are the same as his and Daniels below you.

When I went to fit new pads, you push the pistons back and you simply can’t stop them coming back out quicker than you can get on the rotor/mounts.

Whilst I agree that on other systems like my Hope/Shimanos you CAN do it…. on the RX’s and other Forumlas it’s not been quite as easy as that.

Daniel mine are the same, You can sometimes push the pistons back enough to get the wheel on, but then the brakes are dragging constantly.

Its a shame, I really like the feel of the brakes when they are working.

The shimano’s I’ve used previously have always been faultless.

I think the problem with the RX’s is theres not alot of clearance between the rotor and pads anyway.

I’m not a fan of them personally. They seem to be ON or OFF and theres not alot of modulation

Only heard good things about the shimano brakes so Ill be going for some XT’s next I think

The Shimanos I have have better modulation/feathering of the brakes, but the formulas have a win for outright performance, especially when it comes to the Kevlar pads, they’re just brilliant performance wise.

It’s hard to have them not rubbing at all throughout the whole revolution though yes.

I’ve always thought the opposite to be honest, the shimano’s have a feather light lever pull but they seem to be on or off, where as these are more draggy but I prefer the feel.

Can’t be doing with the faff everytime I change the pads though 😡

There’s something not right but not really any way to know if it’s the brake or the user tbh! If they’re set up right and functioning right, there’s no reason to let fluid out to change pads, the reservoir bladder expands and contracts to make that possible. If they’ve been bled at all since new, they might well have too much fluid in them though.

FWIW I wouldn’t expect to get much effect from a butter knife, I use a massive old screwdriver (the sort you’d never use on a screw, but is great for opening paint pots), it takes a reasonable amount of force to do. Though, perhaps you have a really mighty butter knife.

Northwind, they haven’t been bled from new as far as I’m aware, unless the bike shop bled them (they came on a new bike). Could it be possible that there was too much brake fluid in, which wouldn’t allow the bladder to expand? I thought this might improve after letting fluid out when I did the first pad swap.

I’ll crack out the massive screwdriver and see if that helps!

That ought to rule out overfilling really- it can be a problem if you bleed when the pads are worn but shouldn’t be a problem when they’re new.

I had this on my Oro’s when I fitted new pads, turned out to be the pads backing plate was too big between the pin through the top and the caliper tab on the bottom, when I ground a mm off the bottom of the new pads backing plate they worked perfectly again..

As Northwind says, it’s likely they’ve been bled with part-worn pads in, meaning too much fluid in the reservoir.

I’ve got a set of R1s and a set of RXs and changing pads isn’t an issue. I’d fit new pads and do a full bleed this time, then if the problem is still there come next pad change something else is going awry.

That said I do find them quite awkward to set up perfectly. If your rotors aren’t dead straight they seem to be hard to get them drag-free. But performance-wise they are good.

They came on a new bike so haven’t been bled with part worn pads, I had to let some fluid out after the first set of pads wore out.

I’ll check and see if a decent screwdriver will push the pistons back, if not I’ll give them a full bleed and see if that sorts it. Cheers.

Yorks,

Mine were new on bike too, mine wouldn’t work unless I let some fluid out… I can see why this is weird.. but I can also see why it’s technically correct.

If you have a completely sealed hydraulic system… where would/could the fluid go ?

If you think of the Shimanos etc, they have a reservoir, which you don’t completely fill…. so you have the void where the rubber diaphragm is that can move ‘back’ so the pads can be pushed back.

If the formulas don’t have a similar system, there’s no-where for the fluid to go to… so when you push back then release, the pads return.

I was in the same position as the op last night. My rx’s have never been bled and I was changing the rears for the second time. No chance of getting the pistons in, youd push one side in and the other side would come out.
Like weeksy said I had to unscrew the bleed screw and let a little bit of fluid out.
Makes no sense to me, but it worked.

No idea weeksy, I thought the new type shimano’s were sealed too (the ones where the syringe screws onto the resevoir)?

weeksy – Member

If the formulas don’t have a similar system, there’s no-where for the fluid to go to

They do- there’s a diaphrahm inside the lever body (at the back, usually, with Formula, venting out to the bars)

My RX’s are no trouble at all when changing pads. The pistons always go back no bother with the aid of a large flat blade screwdriver, and the same goes with my Ones and R0’s.

As Northwind suggests – use a big f*ck off screwdriver, keeping the old pads in to protect the pistons.

The reservoir in the lever will cope with the expansion.

Only other thing to mention is that 3rd party e.g. Supersh*t pads are sometimes slightly thicker than Formula pads so can drag initially. To compensate you can release a very small (and I mean very – as in a dribble) amt of fluid from the lever bleed port, or just put up with it for 15miles or so, thinking of how much fitter you’re becoming 🙂

either slightly thicker pads (backing plate or material or both)than the system was originally set up with, or similarly, on original set up the system was filled with the pistons not fully retracted.

Same for me, had to let some fluid out at the lever end when trying to push the piston in on my RX’s last week. I did try a big f*** off screwdriver first but they weren’t budging. Never had this problem with the avids that I was using before. Good news is that they are now working fine.

The massive screwdriver did the job nicely 😛