I've bled 124 brakes many times. Your reservoir is divided between the front brakes and rear brakes. The front 90% or so of the reservoir feeds the front brakes, the remainder the rear brakes. It's easy to run the small rear portion of the reservoir dry when bleeding the rear brakes. The filler neck of the reservoir feeds only the front portion. You have to fill the reservoir until fluid is in the filler neck before fluid overflows into the rear portion. You'll be able to see bubbles from the back to the front of the reservoir when this occurs. Shine a bright light right up to the reservoir to see how full the rear portion is.

I learned all this the hard way. My first time doing the brakes on a 124 was quite frustrating.

I've found it isn't necessary to close the bleeder valve after every pedal stroke on a 124. I've had very good results placing a tube on the bleeder into a cup of brake fluid, opening the bleeder, and pumping away. For whatever reason the fluid doesn't seem to flow back up into the caliper, but rather is sucked down from the master cylinder.

You'll need to top up the small rear portion of the reservoir two or three times to thoroughly bleed the rear brakes.

More than you really wanted to know...

- JimY