Originally Posted by Lonesome George
Riding along today (on a awesome stretch of coast road in Oregon by the way!) and the front brake felt a little shuddery. When I stoped I took the pads out to see if they were OK and there's plenty of life left in them. I then squeezed the front brake with the pads out. Only the top two disks on the brake system moved inwards. I assume all 4 are supposed to move thus pushing the pads against the front rotor.
Am I missing something? I guess this could explain the shuddering if only the top half of the brake pad is being squeezed agains the rotor. Is there anything I can do apart from take it to a BMW shop and get ripped off?
The "disks" you refer to are called pistons. If they're not moving, it just means that there's a bit of dirt etc that's seizing or holding them in place & preventing them from moving.
1. Unbolt the caliper from the bike, stick something (small piece of wood is good) between two opposing pistons.
2. With the two remaining pistons, use a G-clamp to hold one in place. Very gently squeeze the brake lever, the unsecured piston should now start to move as it's receiving all of the hydraulic pressure.
3. Once it's moved out a few millimetres, squirt a bit of WD40 around the piston & clean it well as possible with an old toothbrush or a Scotchbrite pad - nothing too abrasive.
4. Once clean, dry with tissue paper & then smear a little brake fluid around the piston before very slowly pushing the piston back in to place. Ensure that you push it in square to the caliper body & don't push it all the way in, leave it protruding a few milimetres.
5. Repeat for all pistons on both calipers.
6. If a piston refuses to budge, you'll need to remove the caliper & blow it out - I use a compressor blowing through an airline fitting welded to a brake banjo bolt. Works 99% of the time. Obviously you'll need to bleed the whole brake system.