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I'm having a hard time bleeding the rear brake of my Specialized Diverge. Following closely the instructions provided by SRAM (and other sources like GCN and other people from YouTube) only works for the front brake, the rear one always end up full of air in the system. It's funny all videos shows the bleeding procedure using the front brake, but none for the rear one.

Following SRAM official guide, after finishing the step of removing the caliper syringe, I always get lots of fluid coming out. All videos are edited on this part, so I can't know for sure if its normal or not to have so much fluid leak. After that, following all other instructions, the lever feel is mushy and touches the handlebar without any pressure.

Any tips on how to properly bleed a rear brake? What I could possible doing wrong?

  • Links to cited materials (docs and videos) might help to ward off techniques you already tried. – Klaster_1 Feb 20 at 3:32
  • Reference: SRAM Road Hydraulic Disc Brake Bleed. On my bike, fluid leaks @1:45 or @3:15, syringe clamped shut or even with the bleed port tightened. – inibex Feb 22 at 2:40
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On SRAM/Avid brake bleeds it's not normal to have fluid come out when disconnecting the caliper syringe beyond about what you'd expect the bleed screw to displace, or some drops in other words.

When you're doing that, is the lever syringe clamped still clamped shut? (It should be.)

Does each syringe connector have an o-ring and each bleed screw have an o-ring? If any are missing at any point, that's a way air can be introduced.

Have you visually checked the hose for damage? Checked banjo bolt for tightness? Checked the barb/olive/nut assemblies are as they should be? Losing a ton of fluid at the caliper end when you disconnect the syringe raises the question of whether there's a leak somewhere.

When you do the step where you push the caliper syringe while you hold the lever syringe upright, are you applying gentle downwards pressure on the lever syringe plunger, and being sensitive that it is indeed moving up in correspondence with the pressure you're applying at the caliper? If the lever syringe wasn't moving freely during that step, the fluid could get pressurized and maybe spill out that way. Sometimes syringes can get sticky and you can fix it by taking the plunger out and lubricating their seals with brake fluid.

There aren't really any differences between the front and rear procedures. With SRAM brakes it's not supposed to make a difference how the ends of the system are positioned (unlike some systems where you want the lever to be the highest point and the caliper drain plug to be the lowest.)

Doing the actual air bleeding steps, where you push the plunger hard then pull up to coax out air, is a bit of a skill that takes practice. Importantly, you have to get a sense for when you're not seeing anything further because you've actually gotten all the air out versus because you haven't tried hard enough. It's a good idea to tap all throughout the caliper and lever with the back of a screwdriver or similar during these steps, to loosen any pockets of air that might be present.

  • Nathan, I checked banjos, fittings, olives, greasing and the lever (dissembled it and put everything together again). Apparently there's no sign of leak. Syringes are brand new, have a rubber at the bleed screws, and I can move fluid between them, no problems. This video@4:10 illustrates why I should have no leak if the bleed port screw is tight on the lever (or with the syringe clamped shut), but that's not happening. Taking the bleed screw of the caliper makes fluid leak, a lot. – inibex Feb 22 at 2:29
  • I took my time and did everything again, tapped the caliper, hose, lever, and got slightly better results, I can even ride the bike, but the situation is still far from perfect. – inibex Feb 22 at 2:42
  • Just FYI guys, I managed to successfully bleed the brakes. Turns out caliper position plays a huge factor when removing the syringe from the bleed ports. Tilting the bike so the brakes are at the highest point of the system practically eliminates fluid leak. Thanks everyone. – inibex Feb 23 at 4:07

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