Feels like I only have some brakes
 

The car stops but not as quick as before. I feels as if only the front brakes are working. The brake pedel has to go lower to stop and then it takes more pressure. Master cylinder? Booster? Where do I start?

Start by checking for the proper brake fluid level in the rear brake portion of the master cylinder reservoir. And let us know a little more about the vehicle-model, year, etc.

I apologize. The car is a 1983 300SD. The fluid level on the front chamber was a little low but not enough to make any difference.

The fluid chamber for the rear brakes is hard to see. It essentially is filled when the front chamber overflows. I would suggest topping the reservoir just to make sure that the rear chamber is full. This setup has fooled more that a few MB owners.

My guess is that your master cylinder is going. Mine did the same thing your car is doing and I had to replace it. Though I was certain it wasn't my rear brakes because I had just replaced the rotors and discs and flushed them a few weeks before the master cylinder started acting up. If it were your brake booster, you wouldn't be able to depress the pedal much.

Both chambers are full. I learned the hard way about 2 years ago when I was bleeding the breaks and going nowhere fast until I noticed that there were 2 chambers that had to be filled. Is there anything I can do with the master cylinder in the way of rebuilding? If not I will take a trip to a pick and pull to see what they have. Does anyone know if MB used the same part for different models and also what years?

I'm with braverichard - sounds like the master cylinder. You can get a reman for $45 from Autozone.

Two different master cylinders were used on '83 models. What are the last six digits of your VIN? Which is not to say that adequate troubleshooting has been done to positively implicate the master cylinder at this point.

is your calipers sticking? i had poor brakes before teh rebuilt and i always thought it was because it is a heavy car=poor braking. i was so use to it after i rebuilt i constantly lock up the tires stoping.

IF you determine that your master cylinder is, indeed, the culprit, may I suggest replacing it with a new, or rebuilt one?
I do as much junk yard parts shopping as anyone,( and finances are a big concern ) but wear items, particularly wear items associated with vehicle safety are better off left in the junkyard. You just don't know what you're buying. There are exceptions, of course. Like a new MC with fresh paint and a box in the trunk with the old core--like the owner was on his way to return the core after installing it when he was broadsided, totalling the car. But like I said, that would be an exception.
My friend always tells me that MB are so overdesigned that they only need one functioning brake....
(some friend!)