I've just installed a set of disk brakes on my '89 560sec. Once complete I bled the brakes. I am not getting any pressure to the rear brakes. The front seems to be working fine. I get a trickle out of the rear brakes but not the pressure that it should have. Ive read about this possibly being a proportioning valve issue ... What do I do?

You might try filling the brake fluid past the max line, so it flows into the rear of the reservoir. On my 86 300E the res looked full, and I was pumping the pedal like a madman never building any pressure... then I remembered someone mentioning the res had a separate section for the rear brakes which was almost impossible to see. After dumping about a half liter more fluid in there (a little at a time) my pedal became firm while pumping and I was able to get the system filled and bled without any further issues.

Like he said and try to have the car level.

So dont even have the back jacked up a little to better reach the bleeder screws...

The important thing is to make sure the rear section of the reservoir is filled with brake fluid.

jnatewarren, best to use a pressure bleeder instead of risking damage to the master cylinder with the 2-person method. The pressure bleeder will also keep both reservoirs of the master cylinder filled during the bleeding process.

__________________
Fred Hoelzle