When parking in a garage the other day I lost vacuum. Brakes went, no shut-off valve... It happened again today. Driving slow and hunting for a spot - pull up, reverse into spot - brakes stiffen, here comes a parked car towards me... Isn't there a vac. actuator of some sort on the tranny? Since this has never been a prob. at lights or in traffic, should I start with vac. connection to tranny?

mccan,

I think the automatic does employ vacuum for some control functions, but I also thought the vacuum system had some check valves to make your situation less likely. It would seem you have lost one of the check valves as well as generated a pretty severe leak, probably associated with the vacuum controls of the transmission.

Out of curiosity, does the door locking system still work? I would be reluctant to drive the car if the brake boost drops out intermittently.

Good Luck and I hope someone speaks up to help. I think the parts for this system are inexpensive, but they are a pain to figure out and get to at times. Once again, good luck! Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

It only happens in reverse so I assume it is not in the pump but in somehting attached to/controlling tranny.

The only vaccuum to the tranny that I can think of would be the modulator which has nothing at all to do with reverse.

If the linkage to reverse is hitting the vaccuum tube and disrupting it, maybe...

If you lose brake vaccuum, wow that would be a hellofva leak.

I don't know why it would only happen in reverse
Is this coincidence?

It is easy to check for vaccuum with your finger. Take off the small line at the T at the big line to the brake booster and feel if there is some suction. Engine running of course.

If you own an old benz, you MUSST own a Mighty Vac.
This is now a law in this country as well as Germany.

__________________
Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"

What is this Mighty Vac. of which you speak?

Ed, what do you mean the modulator has nothing to do with reverse.... when you get your car up to about 50 mph in reverse the modulator is what shifts you into High Reverse... you could overspeed your engine otherwise... but you must be sure your steering is tight otherwise the car gets squirrely about 65 in reverse , but this is something that should be reserved for professional drivers, particularly if they are experiencing the same vacuum outage as Mccan.... Greg

I think I saw some toothless yayhoo try that on Cops.

mccan:

You can buy the Mity Vac tool at many auto parts stores for about $30 for the basic tool with accessories - the deluxe version with a hard case sells for more. In addition to checking vacuum, you can check the M-B climate control system, bleed your brakes, draw other fluids from places that are unreachable otherwise, engine diagnosis (gas engines, not enough vacuum on diesels), and more.

Good Luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.

Check the condition of the main vacuum line -- putting the car in reverse changes the direction the engine "torques", and you could be opening a major leak when you do so. This has nothing to do with the tranny, you can't loose vacuum through that little hose.

You can lose vacuum from a broken plastic part, where the tranny line connects, that opens up with you put the car in reverse and the engine moves over a bit.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks for the tips. I'll probably pick up a mighty vac. this weekend. I used a $1.99 hand syphon to pull out tranny fluid after I had put too much in. Kind of sloppy.

I took the car out and coasted around the neighborhood. I found that when I kept pressure on the brakes, the vac. slowly decreases until gone. Reversing into parking space was apparently just timing coincidence. Vac. pump seems to be pulling well, but the only check I've done is to put my finger over the main vac. line when car is running. It seems that maybe Vac. Pump is dying and not able to handle the load when brakes make a long constant pull. Or, maybe the brake booster is on it's way out.

mccan

Check to see if there is a one way valve at the brake booster. They are usually replaceable. It should be at the end of the vaccuum line where it goes into the brake booster.

I am too cold to go out and look at mine!

We had snow down to about 500 feet elevation today. What a weird sight to see snow capped mountains in San Jose, CA.

__________________
Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"

mccan,
I've had the same problem on my car. In the beginning I'd loose vacuum in reverse, a few weeks later I'd loose vacuum as you say when applying the brake slowly. The situation was also worse when it was colder outside especially in combination with the car first being started. Over time it took longer and longer for the car to shut off till it would only shut off manually. Both times I had a torn vacuum pump diaphragm. First time - age, second time - my fault. I replaced the vacuum pump diaphragm, used bake cleaner to clean out the vacuum hoses, and a shop vac to suck oil out the brake booster. I also replaced my rubber brake hoses leading to the calipers. Because of the oil contamination I may in the end need to replace the check valve leading to the brake booster. My vehicle does not have a vacuum modulated trans. so it was/is not affected.

__________________
Fred Johnson
1977 240D
1983 300SD

I'll start by checking the Check Valve on the Booster line. how much trouble is replacing the diaphram in the Vac. pump?

Replacing the diaphragm wasn't difficult, a little time consuming. This is an earlier 123 model with a 4 cyl. and the plunger versus the piston type vacuum pump.
On this particular model I took off the cooling fan, 4 bolts (no cluth stuff), loosened the p/s pump and took off its belt to give me easier access.
If your vehicle is a 123 model I have the factory manual that addresses the diaphragm replacement for both type pumps. Also if the vaccum pump is similar or the same on your vehicle to a 123 I could copy and fax over the instructions. The Hayes manual skips over it.
The telltale sign for me that the original diaphragm had seen better decades was when I took the vacuum pump hose off the brake booster and the inside of the hose was wet with oil.

__________________
Fred Johnson
1977 240D
1983 300SD

Mccan:

I have similar problems in my Volvo with a faulty, intermittent vacuum pump. Will tear it apart when warm weather comes.
The "Mighty Vac" is worth its weight in gold. Seriously helpful for all kinds of vacuum issues. Cuts the diagnosis time immensely. I love that little deal with all its attachments (they all come with the package 29.95).
Don

__________________
DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed