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1992 190e 2.6, 1995 e320 Wagon
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Discussion Starter #1
Hey all. I searched but I'm not totally clear on this .. it seems the vacuum is responsible but I'm not sure. I looked a pretty mint 82 300d today. The car is great in all respects except that it doesn't shut off and the brakes barely work. The seller told me that they paid the mercedes dealership 600 to diagnose the problem and that it was all related to the brake booster. Now, reading around here it seems it's a vacuum leak somewhere but ... if it was that simple how did it take the experts at the dealership 5 hours to diagnose?!!
I want to buy the car but I'm worried that it won't be an "easy fix" (troubleshooting the vacuum system based on knowledge from this forum) ..

any input much appreciated!
The car does not shut off. I suspect it's related but I don't know :/

On a side note. There is no rust on the car except at the bottom of the drivers side door. This looks like it would be very difficult to fix, anyone have any experience fixing this spot? These cars are very hard to find around here in rust free shape, in fact, I have yet to see one. This one has come the closest which is why I'm interested in it.
Cheers!
 

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2014 Mercedes-Benz GLK250 Bluetec, 1981 Mercedes-Benz 300D W123
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600 Posts
Hey all. I searched but I'm not totally clear on this .. it seems the vacuum is responsible but I'm not sure. I looked a pretty mint 82 300d today. The car is great in all respects except that it doesn't shut off and the brakes barely work. The seller told me that they paid the mercedes dealership 600 to diagnose the problem and that it was all related to the brake booster. Now, reading around here it seems it's a vacuum leak somewhere but ... if it was that simple how did it take the experts at the dealership 5 hours to diagnose?!!
I want to buy the car but I'm worried that it won't be an "easy fix" (troubleshooting the vacuum system based on knowledge from this forum) ..

any input much appreciated!
The car does not shut off. I suspect it's related but I don't know :/

On a side note. There is no rust on the car except at the bottom of the drivers side door. This looks like it would be very difficult to fix, anyone have any experience fixing this spot? These cars are very hard to find around here in rust free shape, in fact, I have yet to see one. This one has come the closest which is why I'm interested in it.
Cheers!
My car did not shut off when I first got it. and the driver side door lock actuator is broken. My Mechanic isolated the door locks under two minutes and did not even charge me for it.. ever since my engine has shut off immediately after the key is turned. going to get lock actuator fixed soon. I don't think that it can be that big of a deal.. but I don't know about the brake issue... try isolating some vacuum lines ??
 

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1984 300D
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5,064 Posts
If any of that things that operate or create the Vacuum in the system have a leak large enough they can effect the operation of stuff using the Vacuum.

As stated in the previous thread one of the ways to check the various parts of the System is to bypass one part at a time. If you bypass something and the rest of the system starts working you have a good idea that the item you bypassed has a leak.

Bypassing is helpful but it is possible for more than one item in the system to be leaking.

It is possible for the Brake Booster Diaphragm to have a leak. However, what most often causes the problem is the O-ring between the Master Cylinder and the Brake Booster leaks and you lose vacuum there.
Also, the Brake Booster is too expensive (around $300 to $300+) to replace without knowing it is no good.
The same with the Vacuum Pump itself.

The reason the experts might not have been able to target the problem is that there are a Few items it is not easy to hook a Vacuum Gauge to.

The Fitting to T into the Brake Booster line is listed in the Factory Service Manual as a self made tool and while they give dimensions the newer mechanics most likely have not made that tool.

Also if you read the Factory Service Manual the way it is worded is not entirely clear how to test it and what results you will get after the test and some of the test is done with equipment that I believe is an electric Vacuum Pump with a gauge.
 

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1984 300D
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5,064 Posts
These are some aproximate costs from US internet part sellers tor replace the main vacuum system items.

Fuel Injection Pump Vacuum Shutoff $50-$60
The Vacuum Shutoff Valve that is on the Steering Colum Lock and is Actuated when you turn the Key $30
A new Vacuum Pump $365
A new Brake Booster $350

So that is about $850 in parts without shipping and some places will ship free if your order is over a certain amount.

I have no idea what the labor cost would be to replace the above. But, all have been replace by someone as a do-it-yoursel jobs.

I have never priced any of the Vacuum Actuated Door Lock or Climate Control stuff so cannot comment on that.

The Vacuum Shutoff on the Fuel Injection Pump is the easiest to test. If you pull the Vacuum Tubing going to it off and the tubing has Engine Oil ini the Vacuum Shutoff there should be replaced.
While the Vacuum Line is to the Fuel Injection Pump Vacuum Shutoff disconnected hook a generic section of Vacuum Hose you bought from an Auto Parts store to the Vacuum Shutoff; start the Engine and simply suck on the other end of the Vacuum Hose. If the Engine shuts off OK there is a good chance the Vacuum Shutoff is OK.

To test the rest you are best off with a Vacuum Gauge and even better a Hand Held Vacuum Tester (a.k.a Mighty Vac).
 

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2013 MINI Copper S Clubman, '84 300CD-weekend car
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I agree about determining just what the problem is before you can figure out how much the repair will be.

Mentioned above is a device, Mighty Vac, hook that up to one of the two nipples on the main vac line going to the booster. Be sure to plug off the other one, see what the reading is. Should be ~21 inHg. on at least one.
If you have proper vacuum, test the booster itself by hooking up the necessary adapters, to the Mighty Vac and evacuate it, this will take many, many pumps. You're looking for no leaks once you have enough vacuum.
If you don't have proper vacuum, you vac pump may have an issue. There is a check valve on the pump, just before the main line, check that.

I mention this due your description of hard brakes, usually a door lock system leak is not enough to take away sufficient vacuum to give you brake issues.
 

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1992 190e 2.6, 1995 e320 Wagon
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549 Posts
Discussion Starter #6
Thanks guys. I don't have a mighty vac but I'll buy one if I buy a mercedes. My problem is also that the car is an hour and a half away so I have to get it home to do any work on it as well. I wouldn't really want to drive it home in the condition it's in. Maybe it's a pass. I guess I've waited this long, something else will come up.
 
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