"Weather" was right about not having any ABS, even in the rear -- the principle behind ABS depends on knowing when a wheel is locking up, and there is no way for the ABS system to know that except by comparing the speed of one wheel against the others. Without the comparison to a front wheel, it doesn't know whether a rear wheel is locked up, or the car is just standing still.

These cars do not have a 4-channel ABS like newer cars; the 240 has only a 3-channel system, which means that the ABS system gets input from the two front wheels (which you've blocked) and from the differential (the same ring gear as the speedometer, to save money), rather than from each rear wheel separately (which is why the rears don't have the individual sensors like the front wheels). So the ABS system cannot distinguish between the speeds of the two rear wheels for comparison -- the system instead just receives a signal representing a simple "averaging" of the two rear wheel's speeds. In your car, now, the ABS has only one input, and that's not enough for any ABS system to work.

But aside from having no ABS, your braking system is now even worse than that. Prior to ABS, the individual rear wheels (each part of a separate triangular circuit, and that was dropped when the 240 went to ABS) each had a pressure limiter. This ensured that the rear brakes would not be too powerful (i.e., stopping the car more powerfully than the fronts), which is the TUV (i.e., European safety organization) requirement: that in almost all circumstances of heavy braking, the front wheels should lock up before the rears lock because this is considered the safer condition, helping the car to remain pointed straight ahead (and facilitating regaining control) instead of spinning out of control. But your car, with an ABS system, does not have any pressure limiters on the rear brakes (there would be no need for them on an ABS car).

Your car now has neither ABS nor the pressure limiting valves -- need I say more?

Drive carefully, and get the brakes fixed. The life you save may be an innocent someone else.