I just replaced the front pads on my wife's '89 740 GL. Used my standard technique, pull the calipers off the disk, push the pistons back into the cylinders with a c-clamp, new pads & reassemble. Master cyl. reservoir is full.
Now, pedal goes to the floor & only slight braking on the front disks. There was enough pressure to take up the slack on the pads, but no real braking action. With help in the driver's seat, I found that there's no significant fluid flow at the front calipers and no 'spurt' from the 2 lines leaving the rear of the master cylinder as the pedal is pushed. The 2 lines on the front of the master cylinder spurt fluid normally when the pedal is pressed & the fitting is cracked to bleed it.
Any thoughts out there on what could cause the back half of the master cylinder to quit with just a change of brake pads?
Thanks,
Charlie