1983 300td yes wagon.
My hunch is that the booster has failed. Very suddenly the power assist was gone. No warning. I had the usual two or three assisted pumps but no assist since. Now the brake pedal is hard to press and high. And the car continues to run after the key is off.
I have 21hg at the vacuum pump and 20 after the tee. I checked this with a vacuum gauge with the hose disconnected from the booster, and the two consumer lines looped onto themselves.
When I disconnected the hose from the booster there is some vacuum in there. I hear a woosh when the hose is cracked.
Does this confirm a bad booster?
Thanks!

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83 300td 207,XXX

Hard to diagnose without a manual vacuum pump. You evidently have a gauge but you really need a little hand pump. If you have a pump, I would rig up a little set up where you can or could stick a small hose into the front of that power brake unit, right where the big supply hose goes in. Stick the hose in there, use duck tape to seal it off and pump it down - if you can. If you can pump it down and hold 21 inches of vacuum, it is not the problem.

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1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

Think I could rig up one of these to pull and get a reading from a tee? or woud that pump be too leaky?
Nearest mityvac is about 30 miles away- I would love to have one though

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83 300td 207,XXX

I think 20-21hg of vacuum slightly low.

When I had low Vacuum issues it turned out to be the Check Valve that is on the Vacuum Pump. I used a Socket and removed it and sprayed it out with WD-40 and my Vacuum returned to normal.

Others with a similar problem have found the inside of the Check Valve to be Broken.

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84 300D, 82 Volvo 244Gl Diesel

This is a bit of a dodgy way of getting a definitive answer but as you don't have a testing kit perhaps it can help. With the engine off get someone else to pump the brakes whilst you use your mk1 ear to listen out for leaks. If your booster is working well you should hear the leak further down the line at the vacuum pump for example... otherwise you might hear some chuffing within the booster - or if you hear nothing other than the squeaking from the brake pedal or the moaning from from your helper...

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

......and found a spring laying in the pump orifice. The internals of the valve are kaput.



It should look like this, of course-


Would this cause my symptoms of loss of power assist brakes and no shut off?
Can I use a generic spring check valve to replace it? I have a plumbing supply shop within walking disance. They may have something to fit. That would be handy.....


thanks folks.

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83 300td 207,XXX

When my Check Valve was dirty I loss power Brakes so there is a good chance that replacing the Check Valve will restore your Brake Booster. But, it is not impossible for there to be more than one problem.
I PMed info on how to check the Brake Booster.

No one has tried another type of Check Valve so it would be an experiment.

I would think that a Plumging Check Valve would have stronger Spring in it and the Vacuum might not displace the Valve. But, I have never seen a Plumbing Check Valve before so I do not know.


The parts that fell in will not cause you Vacuum Pump to get busted up and the parts from that to ruin your Engine.

But, it could cause another Brake Failure and that could get your Car, Yourself or someone else hurt.

In the pic the Check Valve has an Arrow pointing to it (the pic is upside down compared to how the Pump mounts on the Engine). You see there is an empty chamber with another Valve.
That Vale would keep any Parts from migrating further to the inside of the Pump. But, the parts could hold that Valve open.

The Front Plate on my Vacuum Pump is held on with little Phillips Head Screws. When I remove the Plate I sheared off 2 of the Screws (I guess I was a slow learner).
After that I got out the Penetrating Oil, My Propane Torch and a Manual hand held type Impact Wrench (The type you hold tight in your hand and Hit with a Hammer) with Phillips Head Bit in it. I got the rest out without shearing anymore.

I did not rebuild the pump I just went inside and cleaned the Gunk out of the Valves and put it back together.
Due to the little Screws shearing I put on a light coating of Silicon Sealant on the Front Plate. That was a bout 4 years ago and I have had no further Vacuum issues caused by the Pump.

Attached Thumbnails

   

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84 300D, 82 Volvo 244Gl Diesel

I used a clean shop-vac with a sock on the inlet hose to catch any debris and tried to suck out the rest of the pieces out of the vacuum pump inlet orifice. I didn't suck up anything that I could see with the naked eye.
I now have a personal dilemma. Do I inspect the pump further to find the missing items and risk muffing up other things .....or.......replace the check valve and live with it assuming the pump pulls good vacuum.
Opinions are greatly appreciated!

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83 300td 207,XXX

It certainly will. That issue is probably the most common cause of sudden and intermittent vacuum failure.

That is certainly the only prudent approach. The main problem isn't the failed check valve, per se. The problem is that former check valve components are blocking air flow into the pump. The three valve components (spring, plunger and retainer plate) cannot make it past the pump inlet. I have fished them out with a piece of bent wire and a magnet. If your vacuum cleaner isn't sucking the parts out, they are probable lodged in the inlet. A little dislodging action with a bent wire might solve that problem.

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I don't see how you could vacuum too much out as you would be closing the other Valve that is down there.

Try a Magnet or you could wrap some Tape with the sticky side outwards on a piece of wire and see what you could fish out. The Wire could either be flexiable enough to go in or bent in a curve.
Besure to attach it well or you will end up with a ball of Tape stuck in there.

As far as having to do something that you don't want to do; you can't DIY with out that happening evantually.

On mine once the Power Steering Belt was out of the way the Vacuum Pump came off of the Engine without any issues. That allowed me to get at the Front Plate.

some people have had trouble with the Allen Head Screws that Hold the Vacuum Pump to the Engine. Be sure the holes are cleaned out so the Tool fits in well. Don't want to round any off.

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84 300D, 82 Volvo 244Gl Diesel

I had the exact same thing happen to me. No power brakes, car wouldn't shut off. Problem was interimittent, pieces probably jiggled around while engine was running, sometimes blocking air flow. I fished out the parts, all pieces, 3, with a small retractable claw 2 years ago. Problem fixed. I have never replaced the check valve. I have to start the car to unlock the doors now though...

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1983 300D Turbo, 150K

Yes.... That is your problem. I had the exact thing happen to me a few years ago. Mine was intermittent for a while. Then one day no brakes and I was not able to shut off the car. I actually got that check valve and a kit to rebuild the entire pump. It is not difficult to do.

I would say to NOT do this particular job "half assed". Just get the correct part. NOT having brakes when you NEED them is a serious problem.

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AJ

1985 300D (SOLD)

I fished out the rest of the old valve, put on a new one, and....tadaaaa brakes have returned to normal and the key shuts off the motor.
Thanks to everyone who helped to resolve this issue. Without you all I would not dare own a Benz.

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83 300td 207,XXX