My Whyte came with SRAM guide RS brakes and I was really impressed with both their power and modulation during the summer but I’ve found them pretty poor over the winter months. Once there’s the slightest bit of water/ mud/ grit on the pads or discs all stopping power seems to be replaced with an ear piercing squeal. To the point where I cannot lock up the rear wheel even on a loose surface. Often on a ride if I’ve not used them for a while I’ll go to break and the levers will only pull back a few mm’s.
They seem adjusted correctly with no rub and the disc central to the caliper and I’ve replaced the pads (tried various) and discs (and lightly sanded them to add a little texture to the surface) plus had them bled by my local shop and after every occasion they work perfectly up until they get wet and then all goes wrong again. I’ve tried dragging the brakes to try and clear the discs and get some heat into them but still no luck.
Any tips of anything else I could try? Bike wasn’t cheap so reluctant to just replace them but equally they are currently spoiling what is otherwise a great bike

I have Guide R’s and they squeal like nothing on earth even if I follow the ‘bedding in’ procedure . I have also noticed that the pistons in the caliper are not keen on all working at the same time . I have had to make them work by ‘ locking out’ the other pistons with wedges and then forcing the reluctant piston out. Other than that though they always stop me 🙂

Strange…have you bled them or managed to get oil on the pads? Mine squeal until the 2nd pull, the first I thinks scrubs the water off and the next let’s it start to bite properly…not had any issues with differing lever pull either. Always been consistent.

Ive had problems with the Pistons getting stuck and had to push them back in manually so perhaps this happens during a ride. No matter how many times I’ve taken them apart and scrubbed around the piston to try and free it up they never all seem to push out at the same time/ same amount. Which probably explains the poor stopping power and noise if the pad pressure isn’t even on the disc. Any tips on a way to free them up?
I’m always really careful to remove pads when I work on them so very unlikely contaminated and the fact I’ve changed pads and discs I’d say it’s unlikely to be that

IIRC guides are designed so that one set of pistons hit the disc before the other set as kind of a ‘toe in’ effect like on the old canti brakes.

Messing around with the pistons may mess this up and cause moresqueal than it solves. Just a thought.

I found the OEM pads to be cack, they glazed over and would not be un glazed no matter how much I sanded. They seemed to leave a film on the disc that caused the squealing

Having the same issues with mine, the front 2 and rear 2 don’t come out evenly.
Cleaned the best I can and with a small brush and cotton buds.
Would it be safe to spray with brake cleaner to help clean them properly?

I’ve tried numerous pads with much the same result.
How do I stand taking the bike back to the shop and saying I think they must be faulty either the Pistons are sticking or the seals leak and contaminate my pads? Usually I just moan and put up with it but on Saturday they caused me a pretty nasty crash so feel like I need to get them sorted somehow?

Had the same problems with some four pot Xo trails, tried lods of different pads with the same results. Even tried different types of rotors. Superb in the dry but a mare when wet. Have you tried balancing the pistons? See here ➡ http://www.pinkbike.com/news/tech-spotlight-brake-caliper-piston-service-assessment-2014.html
Ended up swapping to Xtr 9020 trail brakes as I never found a good soloution

They do squeal when wet but usually dry up pretty quick and still retain bite.
I would say they can be tricky to bleed, and my rear took a good few attempts to get right.
The standard pads are pretty rubbish to be honest, I have some Kevlar uberbike ones and they feel much better, can’t say how long they last but if they get through winter then I am happy enough.

Two pairs in our house and they’ve quieter than my Shimanos. I was a bit sceptical of SRAM Brakes having previously used Avids (Emporer’s new clothes) but they’ve been bloody amazing over the past 12 months, silent (even with sintered pads) and reliable throughout.

Ditch the sram pads and get uberbike sintered and get them bedded in proper. Sorted out my noise issues no probs.

4 pot discs will always have a set of pistons moving before the other (6-pots, etc. are the same) – the pistons move as fluid moves around the system, so the closest thing to where the fluid is moving will move first…it isn’t really designed to do it, that is just the laws of nature and how they all work…

Seems as though the saga continues… So I’ve fully degreased and cleaned my discs and calipers. New pads ready to install.
With no pads installed when I pull the lever should all Pistons push out equally at the same time? On mine only one single piston moves at all to the point where it nearly pushes all the way out. If I hold that one in it forces one other out, if I hold 2 in it pushes a third out and I have to hold all 3 back for the forth one to move at all.
This to me suggests that no piston is physically stuck in to the calipers but there is not enough force generated to push all 4 out simultaneously. The brakes were bled by a shop 2 weeks ago so no air should be in the system and the lever didn’t feel spongey. The rear brake is the worst offender but the front is similar. Any ideas?

See my post above…with no resistance, only 1 piston will move. It will move until it stops then the next will, and so on.

Ok if that is the norm then I’ll put it all back together and hope that it was the contamination to the discs and pads that caused the lack of braking power and noise. Thanks