This is how I do it on my 740 with ABS:

Step1: attach vacuum line to bleed nipple, with end going to appropriate container.
Step2: Take a 10" C-clamp and put one end on each side of the caliper.
Step3: Open bleed nipple
Step4: Compress caliper.

That should take care of it. If you do this while everything is still assembled, you don't have to hold the caliper or worry about stressing the lines later. Then (on mine) you can just undo one of the 2 slide pins and pivot the caliper open. Presto change-o Brake job in 20 minutes. No bleeding necessary (but you're supposed to flush ALl your brake fluid every 2 years, so might as well do it now.)

Happy Bricking
William

PS You may need a little piece of wood to cushion the cast metals against the clamp.
--
1990 740 Turbo, on its way to stock specs, maybe beyond

You want to avoid pushing the crud that has settled at the lowest point of the system, from the calipers upward to the ABS or wherever. Use a clamp with a piece of wood to squeeze the caliper back in. I connect a clear hose to the bleeder screw going to a bottle. When it time to push back the caliper, open the bleeder valve and squeeze the crud and brake fluid into a bottle.

Hit the bleeder valve with PB Blaster before you loosen it. I glued the bottle to a piece of wood to prevent it from tipping.

All this is in the FAQ.

Tom

does someone have a picture showing this procedure/

I just take a large set of slip joint or water pump pliers and grip the caliper and the old brake pad and squeeze them slowly to back the piston into the caliper. If your reservoir is full it may overflow as the fluid has to go back into the reservoir tank. It's a good idea to leave the old pad in place so that you put equal pressure on the piston and it won't bind up in the bore.

Are you assembling it in the wrong order? -- caliper should usually be installed before the brake pads. Once the caliper is on, you can slip something (e.g., a screwdriver) between the caliper pistons and the rotor, then gently pry the pistons back in far enough to insert the pads.