I think my vacuum pump has failed on my 300SD, while i was driving i noted my brake pad light was illuminated so i pulled out of the freeway and i lost my brake i had to press all the way to the ground to stop, so i limp it back home, and i tested the air conditioning vents and they will not move, then i tired to shut off the engine and it wont. I brought out my vacuum gauge started up my car and plug it into the brake booster line and what i found is my gauge is bouncing all from 10-15 hg quickly, then i tired pressing the brakes and the vacuum gauge was all over the place. I still have brakes but its hard to stop with it, do you think my vacuum pump has failed??

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Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi

Plug your vacuum gauge directly to the pump and let us know what readings you get.

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1993 W124 300D 2.5L Turbo, OM602.962
2000 Chevrolet Cavalier, 2.4L DOHC
2002 Ford Explorer, 4.0L SOHC
2005 Toyota Prius, 1.5L

http://www.fuelly.com/sig-us/40601.png

Maybe. Could also be a bad check valve.

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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

Disconnect all the lines going to the main vac line, and hook your vac gauge to the line. If there are any other T's in the line plug them. Then remove the main vac line from the brake booster and plug the end. Then start the car and see what readings you get. If you get less than 18-20 your pump is in need of some attention. It shold also hold stead, no jumping around. If it hold stead with good vac, then you have a leak somewhere else. I'd screw the line back onto the booster and read it again. The booster could be leaking.

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First thing I would do is look for a vac pump test procedure. If they go bad they can send things into your cam chain area that you don't want in there. Is the pump making noise?

If you're comfortable running the pump, I would make sure ALL the vacuum lines are secure first, test it, and then start to isolate things that could be leaking. Start at the Booster. To isolate the Booster, I think you remove the main vacuum line at the booster and plug the end while you put your vacuum guage on the first line coming out of it. If that vacuum is OK then your booster is the problem. If not, plug the small line you just had your guage attached to and attach your guage to the next small line and work your way towards the vac pump. Hopefully the pump won't come apart in the mean time.

PS I'd also wait for smarter people than myself to chime in

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1981 300TD "The Green Lantern"
1980 300TD
1983 300D Euro "China Cat"

My brake pedal was hard as a rock when my VP went, softened a bit when I revved the engine and vacuum went up into the teens.

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CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

The Check Valve on the Vacuum Pump is what the Main Vacuum Line screws into just where it scres into the Vacuum Pump.

You can unscrew the Vacuum Line there and after that unscrew the Ceck Valve. I cleaned mine out with WD-40 and low pressure compressed Air.
Also the spring that pushes the disc valves have been know to break so make sure the Valve is under spring tension.
Anway the above cured my Vacuum issue when I had one.

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84 300D, 82 Volvo 244Gl Diesel

Wow, I've been there.

You have some of the most experienced guys giving you advice above, so you're in good hands. Definitely lost vacuum, now you just have to figure out if it's due to a failed pump, or if a large leak formed which would dump all of your vacuum.

Let the leak hunt begin!

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84 300td (Yes, a wagon)
"The Golden Dragon"
195k, 2nd owner
Lives in Redmond, WA

Something is not right, my brakes is working fine now but the car won't shutoff and the a/c vents not operating, what do u guys think I haven't tested the vacuum pressure yet I'll keep you posted. I also warped my rotor and burned up my brake pads too :mad

__________________
Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi

So, your brake pedal went to the floor. I'm pretty sure that has nothing to do with the vacuum pump working or not. What you DID lose is HYDRAULIC pressure.

By your description, I would say you have a frozen caliper, it got hot while you were driving, the fluid boiled which allowed the pedal to go to the floor. When the pedal went to the floor, I'm guessing it damaged the 26-year-old diaphragm in the booster causing a leak. Now that the brake fluid has cooled off. The brakes can once again pressurize hydraulically, but the booster is still leaking, so no vacuum to the accessories.
I would try blocking off the hose where it connects to the booster and see if everything else begins working again.
My guess is that you will have to replace the frozen caliper and the booster.

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-Louis

'87 300D Anthracite

If I lost my hydraulic pressure Than why is my engine not turning off or my a/c vents are not functioning?? Do you think a bad brake booster can cause other vacuum system to not function?? How dose one test a brake booster???

__________________
Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi

Pull and plug the line at the booster. If the car shuts off, and the HVAC systems work, then you've found your leak.
The booster can go bad, it's just a giant rubber diaphragm that stretches every time you hit the brakes. They do wear out over time.

If your car won't shut off then you need to check the vacuum connections - that much has been said - but don't forget the seal between the master cylinder and the brake booster

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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!

You lost hydraulic pressure which allowed the brake pedal to go to the floor. The brake pedal going to the floor damaged the diaphragm in the booster causing a vacuum leak. Yes, that leak will keep you from being able to control your vents and shut the engine off.

You can test it by pulling the vacuum line from the booster and blocking the line. If you can then shut the engine off, you know the booster is bad.

Make sure you find out why the caliper is dragging and repair that issue. This is VERY dangerous! I would also recommend draining and refilling the entire brake system, as well.

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-Louis

'87 300D Anthracite

If you hook up a line to the booster itself and pull vacuum, it should hold, if it doesn't, you have a bad booster. They are quite expensive, so be sure.
There may be a vacuum leak elsewhere, in the HVAC system.
Or, your shut off actuator may have failed. Pull the brown/violet hard vac line going to it and check for any oil there.

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83 SD

84 CD