I am troubleshooting a rubbing brake rotor on the rear SRAM Guide R on my mountain bike. When I spin the rear wheel in the stand it looked like the rotor was out of true. It was nearing replacement anyways so I put a new rotor on. This rotor also looks out of true. I re-centered the calipers which did not fix the issue. I took the wheel off and the outboard pistons visibly much less retracted than the inboard pistons. I cannot push the pistons back into the caliper body with a (plastic) tire lever. I have not tried opening the bleed screw on the caliper yet and thought I would get some advice before I took that step.
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This might help David.
For the basic concepts at least. Could mark your caliper body if you werent careful tho.
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The internet is weird sometimes. I did a fair amount of googling and watching youtube videos and did not encounter this particular video. I’ll give the techniques there a shot as they are different from the others.
SRAM does say not to use DOT fluid on the brake pistons and this video specifically says to do so - what’s the right answer there?
SRAM does say to use DOT 5.1 fluid (and presumably mineral oil for their mineral oil brakes) when installing new pistons. I did this recently, worked great. The above video isn’t the SRAM-sanctioned way of re-lubricating the piston seal, but it probably works OK. The SRAM-sanctioned way is removing the pistons entirely.
As an aside, if the massage technique doesn’t work, full piston service is surprisingly easy. Took me maybe 15 minutes per caliper, and that’s as a first-timer. It’s satisfying to clean out the insides with alcohol and put brand new pistons in there. The piston service is pretty cheap. The official SRAM tools make it far eaier, but they’re fortunately pretty cheap little plastic bits as well.
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Yep that was me reading poorly. SRAM says not to use DOT 5 fluid in big letters on the maintenance manual for my brakes but that’s because DOT 5 and DOT 5.1 are different and they want you to use DOT 5.1. I’ll give this a shot and then do the piston service as it’s pretty clear now that all eight of the pistons on front and rear aren’t retracting all the way.