I don't know why your manual says to bleed the brakes with the compensator torsion bar/linkage disconnected.
I've been doing some checks across various manuals
and am now
nearly as confused as you seem to be - I say 'nearly' because I have the benefit of training and experience on these cars.
I actually found 2 versions of compensator valve that were used on the 124's - one type had a spring that I reckoned might close? the comp. valve as I mentioned in an earlier post (probably fitted on very early models) and a 2nd type of comp. valve (fitted on your later car) whose valve/internal plunger moved outwards under hydraulic pressure (as you suggested) thereby closing off the flow of fluid
if the short end of the torsion bar allows the plunger to move outwards - i.e. under heavy braking, the rear of the car rises, the axle drops relative to the body, the linkage from the rear axle operates the torsion bar, moving its short end
away from the comp. valve plunger, allowing it to move outwards and close off the flow of fluid. Clear as mud, good!
Here's a sectional diagram of the internal workings of the compensator valve,
Top pic. shows the valve in normal position, plunger (they call it a piston) is being prevented from moving outwards by the end of the torsion bar, allowing fluid to flow normally.
Bottom pic. shows the plunger/piston having moved outwards, = valve closed, no fluid being allowed to flow, as a result of the torsion bar having moved away from the plunger due to the axle dropping relative to the body under heavy braking.
I still think that the compensator valve linkage (torsion bar etc.) should be connected and adjusted to ensure the com. valve remains open for successful bleeding of the brakes. And besides, it can't do any harm having the comp. linkage connected and adjusted when bleeding the brakes.
When refitting the brake pipes to the comp. valve, ensure that the metal pipe from the master cylinder goes into the lower port and then the metal pipe going to the rear brakes goes into the upper port.
I discussed bleeding brakes in my post #2. Regardless of the method used, it should be possible to get a good flow of fluid at the rear brakes providing the compensator valve remains open.
I don't know if you have a Haynes 'Shop manual, but it gives a few tips on manual brake bleeding if you're having difficulty. Iirc, you were using a vacuum bleeder and then tried manual bleeding.
1) If doing manual bleeding, have your assistant press the pedal one full stroke followed by 3 shorter more rapid strokes, allowing the pedal to return of its own accord each time. This may have to be repeated a number of times if there is a lot of air in the system. When no more air is observed coming from the bleed screw, tighten the bleed screw on a downward stroke.
2) When manually bleeding the
REAR brakes, pump the pedal slowly and allow one or two seconds between each pedal stroke.
3) If you find that one or more brakes is taking a long time to bleed, the problem may that air is being drawn past the bleed screw threads during the return stroke of the pedal when the bleed screw is still loose - to overcome this problem, only loosen the bleed screw by 1/2 to 1 turn, and temporarily tighten the bleed screw at the end of each downward pedal stroke and only loosen it when another downstroke is about to happen.
