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Uneven pistons on Sram Rival

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Uneven pistons on Sram Rival

Old 01-22-20, 09:34 AM
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Amt0571
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Uneven pistons on Sram Rival

I have a road bike fitted with SRAM Rival HRD brakes. As with all discs, the pistons progressively compensate for pad wear. My pads are about 3/4 worn, and I recently noticed that the front disc started to rub the pads. I could just center the caliper, but I noticed that one of the piston sticks further out than the other.

Both pistons move the same amount when pressing the lever, and both of them retract to their original position when letting go (so no sticky pistons here), but it seems as if only one of them slowly creeped outwards to compensate the pad wear until it started to rub the disc. The rear brake seems to do exactly the same except that it doesn't rub (yet).

I'm not sure if the best solution is to simply realign the caliper until it's time to replace pads, or reset he pistons and make sure they get centered this time. It would also be nice to know why this is happening, but having messed with Avid brakes before, I think it will be impossible to know.

The brake has no air and has perfect feeling. Bled it myself (and I trust myself since I've done it countless times and I don't accept anything less than perfect bleed).
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Old 01-22-20, 01:36 PM
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I've been messing with the brakes the whole afternoon. I've renamed them Sram DoubleCrap and are frankly considering ditching them after less than a year and switching the whole groupset to hydraulic 105.

I've found that one of the pistons was 'semi stuck'. It moved, but not past a point. So the brake only compensated for wear with the other piston. No amount of working out the piston managed to make them to move evenly. No way even after having it sparkling clean. Not even after trying to lube it. I thought it was better to forget about this issue and then...

I decided to replace the pads anyway since they were worn. I was unable to fully separate the pistons, so the disc could fit between the new pads. No amount of pushing and separating with a 50cm long screwdriver did it. I finally opened the reservoir screw to let a bit of oil out and managed to open them to the point that I have 1 micron of space between the disc and pads. Surprising, considering that they have the same oil that came from the factory. The disc now fits but the clearance is so tight it rubs everywhere.

Now, it seems the front brake has less travel than the rear one and has a crappy feeling. No amount of bleeding seems to solve that.

What a good memories of my old Avid Elixirs... I clearly remember when I threw them in the bin and replaced them with SLX that didn't brake as good but required exactly 0 maintenance in 7 years.

The only problem is that replacing road levers means replacing the whole groupset, which costs more than half of what I paid for the bike.

I don't think I want to touch Anything Sram again. Not even with a stick.

I really like the bike, and I'm starting to think about selling it and buying a used 105 one. Thats the only thing sram brakes seem to do apart from braking: frustrate the user until he wants to throw the bike from the top of a cliff.

Last edited by Amt0571; 01-22-20 at 01:41 PM.
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Old 01-23-20, 10:57 PM
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GMBN has an article about to service thes, and it is spot on. I will see if I can find it. (but yiu should search anyways). It involves alretnately letting one piston at a time protrude, wiping the edges of the seal down with brake fluid, and then pushing back in.
At first I thought it was stupid, but it lasts for months if not longer
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Old 01-24-20, 12:06 AM
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Originally Posted by Reynolds 531 View Post
GMBN has an article about to service thes, and it is spot on. I will see if I can find it. (but yiu should search anyways). It involves alretnately letting one piston at a time protrude, wiping the edges of the seal down with brake fluid, and then pushing back in.
At first I thought it was stupid, but it lasts for months if not longer
I did this. Didn't work.

I decided I will remove the pistons from the caliper to clean them thoroughly and really see what's happening, but I'm waiting for a bottle of DOT 5.1 fluid to arrive before doing it. If it doesn't work I'm going to replace pistons and seals, as parts are quite cheap.

In any case, it surprises me that SRAM can't do a trouble free disc brake like Shimano does. 10 years after my experience that prompted me to replace my Elixir brakes with Shimano, and they are still having the same problems.

I have little time to do maintenance work and this type of things make me really mad. I shouldn't have to spend 3 or 4 hours to fix a brake that has been ridden for less than a year and costs 250Ä (that's what they are asking for the brifter and caliper, which is totally mad in my opinion).
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Old 01-24-20, 11:40 AM
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I mean it was working fine before you started messing with it. Most likely you dislodged something into the caliper or misaligned the piston. I've got one HRD bike and 3 shimano hydraulic road discs and they are all about the same in terms of maintenance. Mine are 4 seasons old and on a cyclocross bike that sees lots of mud and can always get them working. Regardless of the system you should be cleaning and pushing the pistons in/out as part of regular maintenance not just when the pads get worn down
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Old 01-24-20, 12:40 PM
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Originally Posted by redlude97 View Post
I mean it was working fine before you started messing with it. Most likely you dislodged something into the caliper or misaligned the piston. I've got one HRD bike and 3 shimano hydraulic road discs and they are all about the same in terms of maintenance. Mine are 4 seasons old and on a cyclocross bike that sees lots of mud and can always get them working. Regardless of the system you should be cleaning and pushing the pistons in/out as part of regular maintenance not just when the pads get worn down
It was not working fine before I messed with it. That's the reason I messed with it in the first place. The piston moved (and still does), but the other one moves faster so only the faster one compensates for pad wear while the sticky one always end up fully retracted after letting go of the lever.

The DOT 5.1 bottle has arrived, so this weekend will be disassembly and cleaning time. I'll report whatever I find is keeping the piston stuck...

My experience with mountain bikes differs a lot from yours. My Elixirs required constant maintenence, and at least a couple of bleeds every year. My SLX has been bled twice in 7 years...and I bled them just to replace the fluid, as they worked OK.

These Rival brakes are giving me the exact same issues that I had with the Elixirs.
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Old 01-26-20, 05:43 PM
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Well... I think I've found the problem. Today, before disassembling the pistons I decided to do one last bleed. I managed to get a really small bubble from the caliper. It seems air somehow managed to get under the piston and it prevented its movement. Now I have a normal gap between the pads and the lever has recovered its normal feeling.

Don't know why the hell I didn't manage to remove it on the three previous bleeds I did,since I followed the sram instructions by the letter.
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