Sticky pistons

[Vladimir]

I had to change my pads mid ride today and as usual, one side of the piston was very reluctant to retract (not handy when on the side of the road!). One pad was also down to the metal, the other one still had some life in it.

The brakes are Avid XOs. Just a dab of oil or something? Obviously not on the pad or rotor!

[Garett]

I had a similar problem on the rear of mine and just took the pads out gave the caliper a good clean with a rag and some GT85. It seems to have cured it for now but it'd probably be best to lube the piston properly as GT85 doesn't really last long. I was a bit reluctant to use grease as it usually ends up being a bit of a dirt magnet.
Obviously be careful about not contaminating the pads when reassembling!
If someone has a better solution I'm all ears because I'm sure there is a better way.

[uncinqsix]

Would a dry teflon lubricant like Finishline work?

[duff]

I thought a bit of brake fluid was supposed to do it, being Avid you'll probably want a bleed kit anyway

[Vladimir]

duff said:

I thought a bit of brake fluid was supposed to do it, being Avid you'll probably want a bleed kit anyway

Strangely, my previous Elixir CRs needed constant bleeding; almost every month! Avid swapped them for X0s for no extra charge and they are 346764454 times better and seem to need almost no bleeding. Fitted them myself. I've got loads of DOT fluid so will try this.

Anyone know what pistons are made of? I know from bitter experience with Juicys that it crumbles if you get a strop on and tw4t them with a large screwdriver...

It's some sort of sintered material not unlike coal...!

[Smartboy]

I have Avid Elixir 5's and find that a gentle scrub with a clean toothbrush (not one you've used on the oily bits) and some brake disc cleaner gets things clean and moving again.

You may wish to mobilise the pistons again by:

Remove pads
Push the pistons back into the caliper (plastic tyre lever is what I use to wiggle them back in)
Hold the working piston in with your lever of choice and then gently pull the brake lever to make the sticky piston move out a little (careful not to pump it out too much)
Another spray of cleaner and a gentle scrub.
Push the piston back into the caliper.
Repeat the process on the other side if necessary.
Repeat the whole process a number of times if necessary.
I don't use anything to lube them, just keep them clean. Perhaps I do need something for lube?

If none of that helps... I would take it to the LBS as I've exhausted my skills and knowledge on this.

[Vladimir]

Cheers all! I will be careful as violence didn't work too well last time.

I'm glad I awkward carry spare pads with me. That metal on metal noise isn't good!

[Vladimir]

Hmm, checked it out today, one piston really is quite stuck (tiny bit of movement) causing completely uneven pad wear; new pads are already looking worn on one side. Accidentally popped the other piston out and splatted DOT fluid everywhere. I'm guessing I need to take them apart to free the stuck one?

I may put in a call to my ex SRAM race mechanic mate!!

[Garett]

I spoke to a bike mechanic yesterday when I dropped my bike in. He said the best way to clean them is use brake cleaner to get rid of the crap and then spray a silicon based lube on the piston.
He also said the Shimano brakes calipers are basically disposable and either you can't get or its pointless getting a rebuild kit with seals etc. Ok if you are using the cheaper ones but he didn't find out until he tried to rebuild some SLX on his old bike!