72 280SE 4.5 Hard Brakes

I have noticed lately that when I try using the brakes they are unusually hard. this phenomenon occurs after driving the car for a while on a hot summer day and parking it for few minutes (to grab a bite for example). I wonder what is causing this? I hope my booster is not going bad. I have recently installed a new brake booster hose but the problem occured prior to this installation. Could I have a vacuum leak somewhere? Any ideas would be appreciated.

[Mark DiSilvestro]

I experienced a similar symptom on a 1972 Mercedes 220 I owned 14 years ago.The brakes worked fine cold but gradually lost boost and the pedal became hard as the under-hood temp increased.
A replacement booster (In my case, used) solved the problem. Hope this helps.
Mark DiSilvestro

[MikeTangas]

When you replaced the booster hose, did you also replace the check valve? It is possible you need to replace the booster unit as already suggested.

The replacement booster hose did have a check valve built in (approximately half way).
Mike, I know you have a 72 280SEL 4.5. What is the proper point gap to set my dwell. My chilton handbook does not have this information however I do know that the dwell angle needs to be 32+/-2 degrees. I had my points changed by a local mechanic few weeks ago and went to check the dwell using a meter and it measured 3 degrees.

[MikeTangas]

Shoot for 30 degrees dwell with new points, set the gap at .4 mm. That should get you in the ballpark.

Someone correct me if I'm off.