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I've got sticky pistons in one of my Sram Code callipers.
I've tried all the usual tricks of advancing, cleaning with isopropyl, applying some dot fluid, retracting, advancing, retracting and so on but they just don't seem to advance uniformly when I reinstall the pads so I always end up with a spongy lever. I've also bled them and am confident that I've done a good job.
The front brake feels amazing, nice and snappy with zero pad rub and this is how I'd like the rear to feel. I am able to firm up the lever feel a bit by removing the wheel and gently advancing them further but they still don't come out evenly so this often ends up with a bit of pad rub.
Is there anything else I should try before buying the replacement piston & seal kit and rebuilding it?
Dot fluid's not a particularly good lube, and corrosive in that use too. A silicone oil (Hope sell Hunters, a plumbers lube, for this job) is probably worth a try before you do the inevitable rebuild.
Dot fluid’s not a particularly good lube, and corrosive in that use too. A silicone oil (Hope sell Hunters, a plumbers lube, for this job) is probably worth a try before you do the inevitable rebuild.
I've read that this is a good idea and also that it's a bad idea because the pistons need some friction with the seal to retract properly. I suppose if I'm looking at a rebuild anyway it can't hurt to try this first, thanks!
You could do with narrowing it down to whether its a calliper issue with sticking pistons there or something in the lever. My one code RSC was slightly sticky, not as bad as the guide that I fixed a little later, but enough that it annoyed me. Knew it wasn't the pistons so bought the rebuild kit and stripped down the lever. It wasn't the piston inside the lever was just an enormous collection of crud around the lever, like seeds and just general gunk. It's been spot on since and you could see the piston wasn't rubbing at all unlike the guide where you could clearly see the marks in the piston which I had to the sand down slightly.
The retraction's a function of the seal flexing(the land it sits in is often cut at an angle to facilitate this) as the piston moves out, and then pulling it back a fraction as it relaxes. There's a world of difference between this and the pistons being stuck to the seals due to wear, dirt ingress etc. It's worth a go, I do mine regularly as I absolutely hate the long lever travel that most accept as normal. There is a caveat, however - your clearances will be tighter, so your rotors will need to be straight, and your calipers perfectly aligned, though this is not a bad thing as your brakes will work far better for it.
Try this method
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I got hold of some Hunter silicone lube, one of those little disc pad spacer thingys and a new set of pads and have just finished the following:
1. Advanced and lubed the pistons - this made such a difference to how the pistons moved that I was suddenly seeing other pistons push back out slightly each time I pushed one back into the calliper body.
2. Pushed the pistons back in and thoroughly cleaned the calliper body with isopropyl.
3. Replaced unevenly worn pads with a fresh set. Turns out the retainer clip was quite wonky too, I'm not sure if this could have been contributing to the uneven pad wear.
4. Reinstalled the wheel, advanced the pads and set the gap with the little spacer thing.
The disc is now running perfectly between the pads and the lever feel is very positive and direct, maybe slightly more than the front even and exactly what I was hoping for.
I still need to bed in the new pads and take it for a ride to be certain but it feels great so thank you all for the help. I think between lubing the pistons and getting the calliper very precisely aligned I've made a big improvement.
I just searched for this lube on eBay, I got some interesting results.....
I just searched for this lube on eBay, I got some interesting results…..
I don't know where I read it but someone on some forum or other was actually suggesting sex lube as a viable substitute. Unclear which flavour is best 🤷
Even though Hope recommend Hunters silicone lube for Hope brakes: the newer Hope brakes have stainless steel pistons instead of phenolic.
https://bikerumor.com/hope-tech-4-brake-levers-and-master-cylinder-deliver-30-more-braking-power/
The seals on Hope brakes are intended to be lubricated with silicone
Formula suggest using Krytox grease
SRAM might not be the same.
Somebody on here recommended Red Grease for the same thing. I bought a tiny tin from eBay which cured my problem with some SRAM brakes.
I find the trick is to follow the usual lube with dot method, pump the pistons several times etc. Then when I clean up, do it with the pistons fully pushed back into the caliper so alittle dot is left against the seal, I never find it contaminates the brake pads.
Then align the caliper with the pads still fully pushed back, just align it to the centre of the caliper. Then when you pump the lever, if any pads drag badly, re-cycle them and adjust how much they are retracted. If you're using new pads, don't expect no drag. After riding and bedding them in, re-check. I find things settle down and then nothing needs adjusting for a long time after.
I find if you adjust the caliper based on the pads, (not the caliper), you inevitably end up with one set of pistons retracted unevenly, and as the pads wear this issue becomes exaggerated.