172 Cup Rear Brakes Doing Nothing

[W111ALG]

Hi guys,

Just looking for a bit of clarity before I start taking things to bits. I am aware that the rear 172 Cup brakes are supposed to do very little and that the compensator valve is disconnected from the rear beam. However I had the car jacked up at the back with both rear wheels off the ground yesterday and noticed that with the brake pedal pressed I could still turn the wheel by hand. I managed to adjust the handbrake so it would apply a pressure and stop the wheel. Is the rear brakes actually supposed top be this bad or is there something wrong here?

I tried manually moving the rear compensator arm up and down but didn't seem to have an effect. I opened the bleed valves on both rear calipers and when pumping the brake pedal fluid is flowing ok. Both rear discs and pads have been changed in last 2000 miles.

Will

 

[mark123]

If you hold the compensator up while assistant 1 presses the brakes and assistant 2 tries to turn the wheels the brakes should work much more strongly. On mine by default you can just turn the wheel by hand with someone stood on the brakes. But if I cable tie the compensator arm up to the chassis the brakes work "properly" i.e. you pull up to traffic lights backwards...