Why do my XT brakes go 'spongy'?

Have a set of brand new XT M785 brakes on my HT.

Both have been properly bled (pushing oil up through the caliper and letting it drop back down/flicking levers etc).

If I flick the bike up onto its back wheel to wheel it through a gate or turn the bike upside down the levers feel spongy. It only takes a few pumps of the levers to bring the feel back to firm but I wouldn’t have thought this should be the case?

My Hopes can be turned upside down all night without any problems. Are all XT brakes like this or is there possibly still some air trapped somewhere?

Thanks.

My xt’s are fine upside down, sounds like some air still in here somewhere

If they’re anything like my saints, when I asked the bike shop to bleed mine they only use the funnel. I asked about the bleed nipple but they said not to bother unless you’re bleeding from fresh and even then you need the funnel to finish them off.

Yup, still some trapped air. In the lever if it goes away after a few pumps.

I had this. It was air in the system. I fitted the syringe into the caliper with fluid in it and the bike upright on iis back wheel. I then flicked the hose from the caliper up to the lever and also flicked the lever. I was surprised by how many air bubbles came out. I kept going until no more air came out, removed the syringe, refitted the cap and wiped the lever and reservoir clean with IP alcohol. Job done. This was despite following Shimano’s instructions when fitting the brakes in the first place, which involved shortening the hoses.

Fudge!

Using the Epic kit so using the screw in syringe with the plunger out as a funnel.

Did any of you wind the servo screw out as I have read before this can have an effect? I didn’t touch it as tbh I’m not sure what it does.

When I bleed brakes, I take the lever off the bike and get the hose as vertical as possible and tap the hose to encourage trapped air to rise. Not sure if it makes any difference but I’ve rarely had any issues with any of my brakes.

With closed systems air between the diaphragm and the brake fluid is the cause.
With Hope and older XT levers you can easily get rid by taking off the reservoir lid, filling to the brim and rolling the diaphragm into the fluid. Modern XT not sure if this can be done, someone may know.

There is a bit of air in the lever which can easily be removed by doing the last stage of the bleeding instructions, this can also be done every now and again between full bleeds if performance drops. With the funnel on the lever half and full of oil angle it up and down 30° and flick/pull the lever blade so bubbles float up into the funnel, it also helps to tap the lever body with a screwdriver handle and tilt the lever so the bleed port is highest.

Thanks, did the funnel on the lever/flicking and tilting levers routine but it’s still there.

Will take them off the frame and hang the caliper below the lever as I bleed to see if it helps.

I noticed it took several goes until i had no spongeyness.

Only trouble I have is I cant seem to adjust the bite point so I have far too much lever pull for my liking, those screws dont seem to do anything? Any ideas?

Bleed the brakes with the little silver screw screwed out. This increases the volume of the master cylinder when bleeding. Then when the brake is bled and fitted you screw it back in and it actually does something.

Regarding the Shimano XT free stroke adjustment > http://www.bikerumor.com/2013/04/11/tech-speak-brake-fluid-break-down-and-implications-for-road-disc-updated/

Free stroke is defined as stroke of the lever before the pads start touching the rotor. The free stroke screw simply changes the starting point of the master cylinder piston. If the screw is all the way in, the master cylinder piston will be all the way in, and the free stroke will be the shortest. Turn the screw out a bit and the master cylinder will start further out. Because it has to travel further before it closes off the reservoir port, the free stroke is longer. In the picture of the clear brake posted above, the free stroke screw is turned all the way in.

I’ll admit that it is confusing because it seems to have the opposite effect when you turn the screw. The stock position is all the way in and that’s where most people like them. If you do nothing but turn the screw out, the pad contact point moves out. So it feels like you’ve made the free stroke shorter. The problem is that turning the free stroke screw also effects your initial reach adjustment. The pad contact point came out, but the starting position came out more. So it’s always at least a three-step process. First set the reach adjustment so that the lever starts where you want it, then adjust the free stroke screw to get the amount of free stroke you want, then turn the reach adjust knob to put the lever back where you wanted it.

I would personally like to see a lever that allows for an even shorter free stroke adjustment but as it is, when the free stroke screw is all the way in, the master cylinder is right up against the reservoir port. So really the only way to give people less free stroke would be to sacrifice clearance between the pad and rotor.

Thanks.

I really liked my Avids.

I could have a cm of free stroke and run the levers close to the bars. Always felt less strained.

Not sure I’ll ever get that with my XT’s

Could be air. Check the hose for kinks too – my XTs go spongy when warm, but it’s only happened after a small crash where I believe the hose got kinked.

(Or to put it another way, I found a small kink in the hose shortly after the crash, and the brakes have been spongy when hot since then too. Maybe a coincidence, but I’d be surprised)

If you’ve had Avids you should be a pro bleeder 😉

I’ve used a couple of tricks from the Elixir bleed process to bleed Shimano brakes. First off degas the fluid in the syringe in the same way you do with Avid, it’s isn’t as necessary due to mineral oil not being hygroscopic like DOT 5 but plenty of air still comes out of solution. The other thing I do is after I’ve pushed the fluid from the caliper syringe to the lever funnel until fresh fluid is coming out I empty the dirty fluid from the funnel and fill it with fresh (degassed) fluid (push the caliper syringe a bit again to make sure any bubbles from removing the funnel come out) then pull back on the caliper syringe creating a vacuum in the syringe and pulling fluid from the funnel down into the syringe. Keep an eye on the funnel fluid level as you would with the gravity method and bag on the caliper tube but the syringe method seems to remove the air bubbles better. I push the fluid back and forth between the syringe and funnel a few times to make sure all the air is out, be careful how much of a vacuum you create with the syringe as it will pulling on the balder and seals in the lever. After this the gravity method produces zero bubbles so I don’t bother with it now but still do the last lever tapping thing.