Can any one help me with this problem , while on my way to work ,I lost my brakes ,can't shut the engine with the key.

When I press the brakes ,its hard as rock , it doesnt go down and car doesnt stop.
I don't know how to check Brake booster for leaks,need some help here.

Checked vacuum and it's :
1. Vacuum with brake booster 10 Hg
2. Without BB , Vacuum pump produces 25 Hg.

Does anyone have a vacuum diagram ?
In this picture what are this lines? I tried to isolate all the outlets on the valve, in order ,and 1st outlet doesnt leak ,2nd and 3rd are bad - vacuum goes to 0.
So the lines that go from valve do leak ,they are routed into the cabin.

Then you aren't pressing hard enough.

You're correct in realizing that this is a vacuum related problem. Now what year and model of car are we talking about?

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

year?

As you know when your primary brakes go out use the hand brake

I have driven a car with the brakes going out. I was able to stop it with the emergency brake, granted i wasnt going to fast.

vacuum pump, vacuum connections or booster

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

Sounds like the brake booster has failed. Put both feet on the brakes and stand on them when this happens. The car should stop with a lot of effort.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

It does sound like a vacuum problem. What you describe is similar to what happens when your vacuum pump fails - but you seem to have good vacuum without the brake booster.

That tends to point to a leaky brake booster. Is it rusty? You may have a pinhole vacuum leak somewhere on it or at the interface to the master cylinder. If you had some way to pull a vacuum on it with the engine off you might be able to find the leak by hissing sound. There's a tool called a Mity-Vac that is made for this.

Also, if you are able to watch the vacuum on a gauge with the car running, try running your hand across the surfaces of the brake booster to look for a jump in vacuum if you happen to plug the leak with your hand.

The leak would be fairly substantial if you are totally losing brake boost.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

I drove back from work today- 30 miles ,like that , when you press hard, i mean really hard and do it 500 feet before stop light ,it will stop.

Problem started last week , rear brakes started dragging, I rebuild the caliper , now the front started the same so by the time i ordered rebuild kit for the front i have no brakes.

How hard it is to replace brake booster?

I know that vacuum before was 20 with BB,when i was setting transmission vacuum few month ago.

brake booster is fairly striaght foward

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

X2. You didn't lose your brakes, just the booster. Stomp on them.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I guess one more trip for me to the junk yard this saturday.
Can one rebuild the brake booster?

^^Not that I'm aware of and they are very expensive. If you can hook up a mity-vac to the booster itself, pull vacuum and see if it holds.

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83 SD

84 CD

You should definitely do some more diagnostic testing before going hunting for a brake booster. One problem is that the vac line going to the BB is pretty big, probably too large to fit a Mityvac into it. You could probably rig up a duct-tape-plus-adapter-frankenstein setup that would work. Or, you could plug the vacuum line at the pump, then hook up the mityvac into the line coming off of the BB and check it that way.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

Does anyone know if brake booster and MC from 1988 420 sel can be put on my 84 300sd ?
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Fastlane lists two different BB's, so I don't think so. The 84 is over $800!

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth