Bleeding SRAM vs Shimano brakes: the differences that catch people out

The difference that matters most is the fluid. SRAM brakes run DOT fluid, Shimano brakes run mineral oil, and they are not interchangeable. Put one into a system built for the other and you'll swell and destroy the seals. Everything else, the procedure and the tools and the order you work in, is detail by comparison. But the details are where people end up with a spongy lever and give up.

Fluid first, because this is the one that costs money

DOT fluid absorbs water out of the air. That's why SRAM systems want a periodic fluid change even when the brakes feel fine: water in the fluid lowers the boiling point, and fluid that boils on a long descent hands you a lever that goes to the bar. It's also why you don't leave a DOT bottle open on the bench.

Mineral oil doesn't absorb water the same way, which is why Shimano systems tolerate being left alone for longer. It's also less aggressive. DOT will strip paint and irritate skin; mineral oil largely won't. Wear gloves either way, and keep both off your rotors and pads.

One more trap. "DOT fluid" isn't a single thing. Check what your brake specifies. DOT 5.1 and DOT 4 are generally compatible with each other, but DOT 5 is silicone-based and is compatible with neither. Getting that wrong is expensive.

How the procedures differ

SRAM uses a syringe at each end, one at the caliper and one at the lever, and you push fluid through and pull it back to move air along. That push-pull is the part that takes practice. You're using the two syringes against each other to drag bubbles out, not just flushing fluid in one direction.

Shimano typically uses a funnel at the lever and a syringe or a simple bag at the caliper, working with gravity. Fluid and air travel up and out through the funnel. It's more forgiving for a first-timer and there's less to get wrong.

Both want the same fundamentals. The lever positioned as the highest point in the system with no fluid traps, the caliper level, and patience. Air moves up. Set the bike up so that up is where you want the air to end up.

Reading a spongy lever

Sponginess nearly always means air in the system, but where the air is changes what you should do about it.

Spongy but consistent usually means air distributed through the line, and a standard bleed clears it. If it feels fine at first and gets worse as you ride, that points at contaminated or old fluid, particularly on a DOT system, so change the fluid rather than just bleeding it. A lever that pulls to the bar and stays there means significant air or a leak, so check for wet spots at the hose fittings and the caliper before you bleed, or you'll be doing it again next week.

A firm lever with poor stopping power isn't a bleed problem at all. That's pads, contamination or a glazed rotor. Plenty of brakes get bled when the actual fault is a contaminated set of pads, and no bleed will save those. They need replacing and the rotor needs a proper clean.

Pads and alignment, while you're in there

Most brake complaints we see aren't bleed problems. They're rub, and rub is alignment.

The method that works: loosen the caliper mounting bolts slightly, squeeze and hold the lever so the caliper centres itself on the rotor, then torque the bolts while you're still holding it. Release. If it still rubs, the rotor is probably a little bent and wants truing with the right tool, not levered straight by hand.

New pads want bedding in. A dozen or so progressive stops from moderate speed, firm without locking up, letting them cool between. Skip that and your new pads will feel worse than the old ones for the first week.

What you need to do it at home

A bleed kit for your brand, the right fluid, a torque wrench, isopropyl alcohol and clean rags. The kits aren't expensive, and after two or three bleeds you've covered the cost against workshop labour.

The honest caveat: your first bleed will take considerably longer than you think it will, and doing it once next to someone who has done a few hundred saves most of that.

Learn it hands-on

We run Brake Bleed and Pad Replacement as a Thursday evening Skills Night at the Annandale workshop. Two hours, $119, six riders maximum. We cover SRAM and Shimano systems, pad replacement, caliper alignment and rotor truing, and you do the work on your own bike with proper tools.

Bring the bike with the brake that's been annoying you. That's the one worth learning on.