i've SLX on my bike and they've been fine. mate has recently bought 2nd hand XTs. the front is fine (same feeling to my SLX). the rear brake, however, has no modulation what-so-ever.

you've about 10mm of lever throw till the pads are tight up against the disc giving a very woody feeling.

i've cycled the pistons in-out-in-out, put a drop of oil on them and given them a clean.

i've checked the caliper for air.

i've let some oil out of the system at the lever thinking that the system was over-filled.

got everything where it should be (pads back inside the caliper, pistons withdrawn) and topped the system up.

thought things were giong well untill we put the pads and the wheel back in and were left with the same problem as that we started with.

the lever throw is to the bar. on the second stroke it feels fine. on the third stroke everything is woody again.

the pistons aren't returning to 'start'. the lever throw is limited to 10mm or so.

short of bleeding the whole system (which i don't think will help) or buying a new calpier what can be done?

any help much appreciated.

cheers

J

Piston seals fecked so they aren't returning?
Oil not returning to reservoir when the lever is released somehow?

You're imagining things, everyone knows shimano brakes never go wrong…

Oil not returning to reservoir when the lever is released somehow?

yup, exactly.

the pistons were quite dirty when i pushed them out to clean….

I have XT brakes and bled mine on two different bikes. The brakes work fine and the lever goes stiff after only about 10-15mm or movement. They do feel very solid but it would be nice to have a bit more lever throw before they come on. They have been bled form caliper and reservoir, I do not think they are over filled. Would be grateful for some advice if anybody has any. The bite adjustment screw does not seem to do anything.

Not saying this is it, but one problem I had with my XTs was at the caliper. the little dust cap on the bleed nipple was missing and unknown to me dirt had got packed into the bleed nipple. So, when I did a 'bottom up' bleed, I just pushed a load of dirt into the system. Not realising this at the time, It caused me weeks of hair pulling out, until I eventually stripped the whole thing down and removed and cleaned everything that could be removed and cleaned as a last ditch effort.

The bit adjustment screw does not seem to do anything.

same here…

not found that i've ever wanted it on the SLX.

the little dust cap on the bleed nipple was missing and unknown to me dirt had got packed into the bleed nipple.

nipple is clean… oil flowed out clean when opened…

if you are basically saying that pumping lever a couple of times makes brakes work better then it is prob air trapped / seals in lever damaged or worn so they are not pushing fluid correctly to activate pistons. non returning pistons can also be air trapped as there will be less vacuum effect to pull back pistons.

one test is to take wheel out put large screwdriver between pads pull lever and hold. if you can push pads back with screwdriver to any extent while holding brake on then prob air.

make sure you use fluid that isnt too old and should be left to stand for a few hours so no air bubbles in it.

Im not sure mineral oil is hygroscopic though.
Have you bled from the caliper up to the lever? It can take a couple of goes to get it right.
Try also once you've bled them leaving the lever pulled in towards the bars and zip-tied overnight, often helps some of the remaining air to rise up into the reservoir (try tapping the hoses to help the air move upwards).

true mineral not as hydroscopic as dot

done the air check thing with the screwdriver earlier. it's not air in the system….

i've bled my brakes a few times and know how it works. just didn't/don't want to do it if it is not 100% necessary.

just been to the LBS and had a pull of the levers on all the bikes equipped with XT brakes.

all have a similar, more woody feel to them when compared to my SLX. it maybe that that is the norm. we also rode up the hill and down a couple of times and now there is a bit more throw in the lever and the pads have more bite.

might try the cable tie/lever thing though. see if it helps.

cheers guys.