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I recently had my bike serviced and things were fine. However, for some reason, the brake levers (front and back) are slow to return and both pads are rubbing almost like they've been overfilled, or become contaminated. I've looked up the issue with the SRAM pistons expanding, and it looks like that's worth doing, but would that also have caused the rubbing? It seems a bit dubious that I could have been affected by both. Though that could have just been a bad bleed potentially.
I'm assuming my options are, try a bleed and see if that fixes the issue.
Failing that, try the piston replacement with the aluminium pistons.
I'm guessing the piston replacement is worth doing anyway, and it'll need a bleed afterwards, so I may as well get both of those in at the same time?
Failing all this, I have a pair of XT brakes hanging about. Should I just cut my losses and go straight to replacing the brakes, or are the Guides worth trying to salvage? I do like how they feel, but generally, the Shimano brakes on my other bieks have been less of a faff. What would you do?
Might be worth calling the bike shop to ask if it has just been serviced.
A few years back I had an issue where I bled my brakes in the garage one evening in winter, about half way through I got so cold that I finished the job in the kitchen. I left the bike in the kitchen overnight and when the heating came on the next morning, the fluid expanded and locked the brakes on. I popped a rag against the lever and let a bit of oil out and all was good.
I am not sure if mineral oil is that sensitive to temperature changes or it was just a bad bleed with some air that expanded as it warmed up?
The brakes can definitely rub if the lever piston hasn't returned fully. So it might well be related. It's also the warmest it's been for at least a year, so a temperature-related thing is certainly plausible.
Brakes aren't that complicated really. If they're rubbing, it's pretty much either alignment, a bad bleed, sticky caliper pistons or sticky lever piston.
I would try opening the bleed port on the lever and squeezing the brakes on and off a few times. If they have been overfilled, that should let any excess fluid escape.
Edit. Also worth removing the pads and cleaning around the pistons with hot soapy water, then dripping a few drops of fluid onto the pistons, then forcing the pistons back into the caliper. This should make sure the pistons aren't sticking.
thols2
I would try opening the bleed port on the lever and squeezing the brakes on and off a few times. If they have been overfilled, that should let any excess fluid escape
Indeedy I've done this before now to resolve rubbing with new pads, though you need to re-pressurise the lever as it run at a higher pressure than the hose... apparently
See 10.48 "Balancing the system"
Personally I've had the lever go a bit weird on both my sets, but continued to ride them, and they came back to normal.. still not replaced the internal pistons.
you need to re-pressurise the lever as it run at a higher pressure than the hose
That doesn't make any sense. When the lever is released, the entire system should be at atmospheric pressure. When the lever is pulled, the reservoir should stay at atmospheric pressure and the master cylinder and hose will be at higher pressure. The master cylinder, hose, and wheel cylinder are all connected so the pressure will the same throughout the system, apart from a tiny difference due to the height of the master cylinder above the wheel cylinder.
Cheers, TBH, I'm on the lookout for a new LBS so asking them to have a look again is out.
So it sounds like my options are:
- Try and siphon off the excess fluid from the lever end so it doesn't rub.
- Check for a sticky piston. Should be able to do this in the stand.
- Clean off any gunk on the piston if it's not retracting as expected.
- Ride it a bit and hope things get better 😀
I'm not an awful mechanic, but it's the time I don't have. I guess it's worth a go, becasue worst case, I'll need to find a new LBS to have a look at bleeding it, best case, I fix it and I'm good.
Sounds like the sticky piston. Fairly easy fix and I ordered the R2 pistons from ebay via Taiwan. Certainly temperature related at first, then they stick permanently.
You can 'modify' then yourself, but you'll need fine sand paper and take off some of the plastic - you'll see scores on the piston where it's stuck. The R2 piston has a much smaller diameter. Don't try and remove the seals as they damage easily.
Since the fix my Guide RS have been absolutely perfect. The bike is 5 years old and has had the fix at least 2 years ago (by me).
Nice one, got a link to where I can source the replacements from?
I did the mod myself with sandpaper - worked great for 2+ years until I snapped the lever completely (replaced with G2).
However, if I was doing it again, I'd buy the SRAM lever tool otherwise it's a PITA to get everything reassembled.
The lever tool is needed on the RSC - It was OK on the RS. You'll need some fine point 'bits' to remove the circlip and fine flat head screwdriver (you'll bend the circlip getting it out) as I couldn't get circlip pliers in, too tight a space. There is then a washer before the piston. On replacement, refit new piston, and push down the washer. Then gently push the washer into the circlip recess in the lever. This will keep the piston in place as you refit the circlip. You'll have to bend the circlip back into shape, unless you can find a small enough plier.
Little fiddly.
PS It's the longer piston in the RS.
I tried the ebay pistons, but they made mine worse!
The SRAM lever rebuild kit worked a lot better.
Bloody hell, all this just to get some brrakes to work!
How does the piston setting kit work? I checked YouTube and I tried to find the manual for the tool on the SRAM site, but there's nothing in there about how to use it.
On the plus side, today must be a little bit cooler as m brakes are not as slow to return anymore!