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So I finally have my wife's bike almost put together. The only thing I have left is the disk brakes. It's the new XTR disks. I'm a pretty good bike mechanic but I've never had to deal with disk brakes before. The instructions that came with the brakes suck. Do I fill up the line with mineral oil before putting it on, or do I assemble everything first and then bleed the lines.
Thanks for any help.
Like any other system that needs bleeding it is important to get all the air out. I would put the bike in the stand, mount the lever and let the caliper hang straight down. All the air blubbles will 'tend' to float upwards. In my experience it is easiest to force the fluid from the caliper to the lever. This will force all the air out. If you did not get one I would get a Shimano bleed kit. It might be a little expensive but it will make it easier and the brakes will work much better. One word of caution, don't get any mineral oil on the pads or rotor. The pads will suck it in a be destroyed. Ideally you would have old pads to install in the caliper but that doesn't seem the case. You depress the lever (i use a rubber band or clamp), pump fluid in and then close off the system. Remove the clamp, pump the brakes a bit, flick the hose to remove air bubbles and repeat the bleeding as necessary.
It is possible to bench bleed the system but it is a messy pain in the butt. I would grab an extra set of hands from someone to help. This may help decrease the chance of getting fluid on the pads. FWIW I have some 4 pistion XT brakes that have not been bleed in years and have mineral oil from my local ACE hardware in them. The Shimano stuff is expensive and unless they made the new stuff super special don't sweat about using it.
Thanks for the tips Mike. Hopefully I'll be able to get everything to work right.
David