Brakes Question
 

Got a question on my 300D's brakes. Are the brakes on the w123 supposed to be hard to lock up? 'Cause i drove my friend's 1977 Chevy Nova (6 cylinder :() with a front disc brake and rear drum setup and those brakes were very easy to lock up. Does this indicate a fault in my brake system? I do believe there is excessive brake pedal travel. Perhaps the brake pedal can be adjusted so that there is less free play? Or are 4 wheel disc brakes harder to lock up?

Hmmm.
 

1985 300D Turbo, 194,600 miles.
This is all guess work without further diagnosis. :)

Is there vacuum being supplied to the brake power booster = possible vacuum supply problem.
Air in system = bleed total system.
Possible seized caliper = rebuild or replace bad caliper.
Possible bad flex hoses = replace all four rubber flex hoses, they break internally and block flow.
Possible bad master cylinder = replace with new.
Brake tube to rear broken = leak = replace tube.

There is vacuum assist. The pedal moved downwards when I apply the brakes and then start the car (after pumping the brakes to deplete vacuum). Bleeding the brakes sounds like a good idea. I found some brake fluid at Kragens that says it *exceeds* DOT3 and DOT4... is it ok to use? I don't have any jackstands, though I dont think this poses a problem...

yes, it's OK, that's just typical marketing hype. It *meets* the standards too, and *exceeds* them as well, like nearly every other brake fluid out there. Properly operating brakes should be strong enough to lock the wheels, front and back. Not that you want to stop that way, but for checking performance, yes. Disc brakes are generally better performers than drums, and your rear brakes should definitely be able to lock if they are in good shape as there is less weight on them when you are decelerating going forward.

Double check that the resevoir is full. The rear brake section of the resevoir feeds off a small hole near the top of the fill hole. This means that you have to fill it to the top to let it run down that hole. If the rear brake section is empty (or near empty allowing air in lines), then you will only have front brakes and it will reduce your ability to stop and be near impossible to lock up.