My brakes are real unresponsive and it really takes some force to brake effectiveley. The pedal pretty much goes all straight down with very little resistance and a little squelching noise from the arm of the pedal itself. There is the proper amount of brake fluid, front brake pads have about 70% and rear pads have about 50%. This concerns me as it might start snowing next week. Also my car wont shutoff when the engine is still cold. I am assuming this is all vaccuum related. So, I have some questions for those inclined to answer:

1.With a vaccuum gauge, where and how do I test the functionality of the brake booster, vaccuum pump and shutoff valve?

2.How would I know if this is the master cylinder?

3.What else could this be attributed to?

4.What is a typical brake boosters life expectancy?

I really appreciate all the help everyone has provided on this board.

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1983 300SD White with Grey interior

I'm not extremly farmiliar with the the vaccume system on the car. but i'm very farmiliar with the breaking system. i think you have a vaccume problem, but the way you test this when it comes to breaks is: with the car off, step on the break a half dozen times and then step on the break firm and hold it there. then start the car. the peddle should sink about 3 inches. if it dosen't sink then there is no vaccume getting to the booster. if it sinks then stop the car. you should be able to setp on the breaks about 3 times and the peddle should get progressivly harder, after 3 steps the peddle should be hard. if its hard right off the bat, thats because the check valve that should be holding vaccume in the booster is bad.

with the shut off problem you have i'd bet its because there isn't any vaccume, that means there a leak some where or the pump is bad. but like i said i'm not expert on that system. but i'm sure there is some on here who can talk to you about that.

Unless you are losing brake fluid or have a rusty brake booster, I would look at the pump needing rebuilding. To check vacuum for this, anywhere along the large line from the vacuum pump to the booster would be a good place to find out what the pump is putting out.

The pump is fairly easy to rebuild. The only thing I ran into is one of the hex drive screws was rounded, (Hint: remove the ones hardest to see and access first.) and the rebuild kit was not the correct one. (Ensure it is for a "late-model" pump). You can replace the check valves, etc. while it is on the car but you will be unable to verify the condition of the hardware side unless you remove it.

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Sam

84 300SD 350K+ miles ( Blue Belle )

What is the optimal vaccum pressure on the line (does the car need to be running to check this)? How do I Know if my pump is a late model? Could acheck valve be a problem here?

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1983 300SD White with Grey interior

Rebuilding the Vacuum Pump on the 617 Engine
http://diymbrepair.com/easley/Rebuild_vac_pump.htm

Vacuum pump lesson learned
http://www.peachparts.com/shopforum/showthread.php?p=872760#post872760

Vacuum Pump Gasket Sealer & Torque
http://www.peachparts.com/shopforum/showthread.php?t=138153

1982-240D-Vacuum System
http://www.peachparts.com/shopforum/showthread.php?t=105201

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1985 300SD
1983 300D
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Thirteen inches of vacuum is minimum for the system.
In theory the pump can pull thirty inches of vacuum.

OK, I'm confused.

1. Does the pedal go all the way to the floor?

It should not go more than about half way with reasonable force. Too much travel could be from air in one or more brake lines or a master cylinder problem.

2. Is the pedal hard or easy to press when the engine is running?

It should only require firm pressure to stop, not really a hard stand-on-the-pedal action. A hard pedal with otherwise good braking action could be from a loss of vacuum, or a leaking booster.

3. Is the pedal hard or easy to press when the engine is not running?

[It should start out firm, and get more difficult after 2-3 presses. If it is hard to press immediately after shutoff, it could be a bad vacuum line check valve.

No shutoff is a symptom of no vacuum to the fuel shutoff diaphragm, from a leaking diaphragm, a leaking hose/fitting, or a vacuum pump producing low/no vacuum.

These may, or may not be related...