Having problems with 1979 300SD. Hard braking, wont shut off etc. I have read many threads on these things and am begining to wonder if the vacuum pump is providing insufficient vacuum. I hooked an old vacuum guage to the small line from the pump(kind of whiteish in color) to the various branchings. It read 5" of vacuum and increased to 9 or 10 when the engine was revved, somehow I expected more.

The engine shuts off if you suck on the vacuum line(brown with blue stripe), so it may be the key switch at fault(no oil though), but if the whole system is not getting enough vacuum supply couldnt that also be the problem?
Anyway if anyone knows what the vacuum readings should be at the pump or other important locations it would be a help.

Vacuum pump shoud be around 23-25 inches new. So disconnect all vacuum users and measure again. Disconnect the booster and block the hose ( a thimb does well) and include any feed lines. If not showing 22-25 inchs then its the vacuum pump. If it is showing the normal vacuum then we go from there.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Thanks,
The vaccum at idle was initially about 6, gradually increased to about 9 or 10, and reached 16 at high rpm. So are there any gotcha's to r&r on this thing? I'm going to go price a pump and will check back later....

Sadie,

Just got finished rebuilding mine....same symptons as yours, only 10-12 inches was max. It had a broken check valve. The rebuild kit is pretty pricey, about $70, but is far less than a new pump, $275. There is a good set of instructions on the DIY pages.

Good luck!

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold

Might just be the brake booster hose. That solved my wifes low vacuum problem on her 300D.

I can't seem to find the part on Fastlane.. the '79 300SD has a booster hose right?

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'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.

You should hook up the gauge directly to the pump with no hoses and eliminate any chance of a vacuum leak. If the vacuum is still weak, you know it's the pump.

__________________
1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold

Thanks for your input.... I did actually hook the vacuum guage directly to the pump and plugged the brake booster line with my thumb.
Looked at rebuild kits in fastlane and there was a diaphram kit and a valve kit. How do you know which is needed? JUst get both?
Also couldnt find much of anything on the DYI page, six or eight articles, none on related topics. I assume that as a total newbie I am not looking in the right place?
Cant begin to tell you how helpful this Forum has been, hope someday I have something useful to contribute.

Sadie(newbie)

Hello group... Im still not sure what rebuild kit to get and have not found a source for a rebuilt or new vacuum pump. any ideas?

Try this for ideas:

http://business.baylor.edu/Richard_Easley//autofaqs/Vacuum%20Pump/Rebuild_vac_pump.htm

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

There are two kits available for an 81-85 SD. The cheaper one is the one you want ($71 on Fastlane), considering that your pump is pulling some vacuum. The more expensive one has a new pusher assembly, which you probably don't need ($262 on Fastlane). When the pusher assembly fails, you get no vacuum at all and you also get ball bearings inside your engine. Performance Products also has these kits for sale.

If your engine is not an original 81-85 SD engine, you should get the engine number off of the driver's side of the block, just below the head, and in behind the oil filter housing. It should be a number that starts with 12 and looks like this 12-xxxxxx. Call Phil and he can tell you which kit you need for that engine.

Good luck!

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold

Well I re-read your original post and see you have a 79 SD. So you have two choices for a rebuild kit, depending upon your engine number. For engine number less than 014182 you will need a diaphram kit and for greater than 014182 you will need a piston rebuild kit. Sorry for the wrong post above.

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold

Try searching the Diesel forum, hopefully you will get lot more info. on the vacuum pump rebuild.
Good Luck

__________________
87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)

Okey dokey... with engine#014083 Im gonna order the diaphram kit and a gasket so I wont have too make one. Im kinda nervous though about the replacement procedure. Checked the link above(thanks for that) but it only discussed the piston type procedure. Im guessing the diaphram style is a lot easier, at least I hope so. Havent found any other specific information so Im gonna wing it when the parts arrive.

your most grateful
Sadie