I’m trying to bleed my xt brakes after a poor job of shortening the hoses. I’m going for the reservoir down approach (opening the nipple with a bit of hose on it, squeezing the lever 2/3rds, closing the nipple, releasing the lever and topping up the reservoir when necessary) I’ve put a lot of fluid through the system (over 100 ml) but I still seem to be getting small bubbles coming through. I gave up last night and refitted the brakes, they feel moderately stiff but I still think there’s room for improvement.

I could concieve it if there was air trapped in the system I couldn’t get to and I saw nothing coming out but still got spongy brakes but surely this implies I’m continously letting air in? I’ve been topping the reservoir before it get’s too empty (about half full) What am I doing wrong?

Keep the bleed nipple closed. Pump the lever a few times to build up pressure and keep it squeezed when the pressure is up. Open the bleed nipple and keep squeezing the lever until it touches the bars. Hold the lever to the bar, do not release it. Close the bleed nipple. Release the lever. Repeat a few times keeping the reservoir topped up. This stops air being drawn back into the nipple when you release the lever with the nipple open.

Other things to try are tilting the bike so that the brake caliper is higher than the reservoir (keeping the reservoir level of course) and bleed as above – this can help the air flow up to the bleed nipple and not back up to the reservoir. I have done this with the brake off the bike and the caliper positioned above the reservoir clamped to a shelf. You shouldn’t need to go to that extent though.

Once you are done, or as good as you can get it, pump the lever up to pressure and tie it up so that the brake is pressured and leave overnight. This pressurises the fluid and makes any tiny air bubbles float to the reservoir more quickly where it pops up to the diaphragm.

Blow it through with a syringe from the bleed nipple on the caliper with the reservoir open and level and a pitcher underneath to catch the fluid. You could do variations on a theme by sucking a little before opening up the reservoir to make sure the caliper is devoid of bubbles. I’ve heard folk preaching the virtues of the way you’re trying but personally I think it’s a waste of time.

Mary Hinge’s last ploy does sometimes work…but after doing it, open the reservoir and blow it through with a syringe from below.

please also bear in mind that if your lever/reservoir assembly is knackered you will get continued problems whatever you do.

Thanks! It’s a new set of brakes hence the shortening so I’d hope the lever/reservoir assembly is still ok. I did have a syringe ready to try the reverse method but for some reason I couldn’t get it set up so that there was no air in the tubing attached to the nipple, it always seemed to draw a little back in, even when I forced it out. I didn’t fancy squirting that into the caliper!

Also I was doing this with the brakes off the bike, lever attached to a set of handle bars in a work stand with the caliper dangling so your saying I should have it the other way round? caliper elevated? My rationale was that there were more nooks and crannies for the bubbles to float into if the caliper was the higher.

Tapping the brake hose with a screwdriver sorted my SLX’s.

Mat – think about how air will float to the top of fluid, you are trying to push it down an inch or so at a time. So a bit will keep trying to get back up to the reservoir.

You need to find a way of clamping the caliper above, or at least level to, the reservoir, so that the air floats up to the bleed nipple.

It’s not that critical to get the caliper higher, level or almost is fine. Just try to be fairly swift with the pump/bleed/pump/bleed/top up/repeat and it should be fine.

If you aren’t far off now i.e. if you get enough pressure to make the brake work, just tie the lever back overnight, with the reservoir above the caliper so that the air floats up to the reservoir.

I have found that letting all the fluid drain out and staring from empty is more successful than bleeing whatever fluid is left in the system. Also lots of tapping on the calipers and hoses.

+1 for the push up from the caliper option

Couple of other things

– start with the freestroke screwed right in. Then when all finished screw it out. This gives a very solid feel when all is done
– at the end I close off the reservoir then pressurise the system from the caliper by pushing the oil in the syringe into the system then closing off

And good luck, great brakes IMO