Hi,

I have a 1983 300d with 168K. While on vacation in Vermont all of a sudden the brakes would not respond on the highway, the brake pedal was very high and it took a great deal of force to get it to stop. I pulled over to the side of the road and the car would not shut off either so I realized I must have a vacuum issue.

I spend an hour on the side of the road looking for any obvious signs of the leak and to make a long story short I found what might be the cause. I was checking the hoses that go through the firewall by removing the panel under the dash board and saw the "black" hose was not connected to anything after going through the firewall. This is a very difficult area to work in and I could not see any connection that the "black" hose would connect to. It looks like the dash board would have to be removed to get a full view of the area.

Knowing no mechanics in the Killington Vermont area I decided to carefully make the 4 hrs trip to New York to swap cars and work on the issue after vacation in a week.

Any suggestions on where this "black" hose might go would be great. Do I have to remove the dash? My manual has no vacuum diagrams.....are there any out there?

I have had an additional problem that happened at the same time, the ignition switch will not start the car. I installed a started switch (in the engine compartment) several years ago that goes directly to the starter because the ignition switch would occasionally not work. Someone recommended going directly to the starter with a remote switch so I installed one for the rare times it would not start. Now that happens all the time and I have to use the remote started with the key in the on position. Could this be related to this whole vacuum/brake issue?

Sorry for the long post but I am hoping with everyones help to hit the ground running when I return home!!!

Sincerely,

Bob K

1983 300D 168K
1990 300E 88K

Black line is not your problem. That is a vent. Given the complete loss of vacuum, you need to check either the main line or the vacuum pump itself. Put your Mity Vac on the main vacuum line from the pump to the brake booster and get a reading then report back. Chances are the main vacuum line is cracked or broken or the pump has failed.

Not sure about the connection with the starting problem. There is vacuum thru the ignition switch so it is possible there's a connection.

__________________
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

odds are good you have lost your vacuum pump, or brake booster. I would unscrew the line from your booster and stick a small cork in it, and see if your car will shut off now.
if so, you have a ruptured booster. if not, unhook one of the lines from the tees on the main vacuum line and hook a mity vac or a vacuum gauge of some kind on there and see if there is any vacuum present. start plugging off everything that leaves the line until you have vacuum or everything is plugged off. once everything is plugged from the main line if you still have no vacuum, inspect the main line from one end to the other, for cracks or tears. if it's perfect, order a vacuum pump rebuild kit, or pull a used pump from a junkyard.
the starting issue is likely the neutral saftey switch. try starting it in N instead of P if that helps, try pushing on the shifter all the way forward. that helps on my 83TD.
the fix is to crawl under the car and replace the plastic bushings that connect the shifter to the transmission linkage.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Thanks for the quick replies! It looks like I was wasting my time on that black vacuum hose! When I return from vacation next Tuesday I now have some direction and will report back.

Sincerely
Bob K

Right where the Main Vacuum Line screws into the Vacuum Pump there is a Check Valve.

It can be unscrewed, inspected and cleand out with WD40.

It is very common for the Plastic Nipples in the Middle of the Main Vacuum Line to crack off.

__________________
84 300D, 82 Volvo 244Gl Diesel

Just got home from vacation and will get started on the vacuum testing tomorrow and will report back then.

I wanted to add information on the starting issue: I tried to start in neutral, park and slowly worked the shifter through all gears with no luck. What I do get is a clicking noise coming from near the right of the ignition switch behind the dash. The dash lights DO NOT dim at all. The battery is testing 100%.

It will always start when I use the remote started switch I installed under the hood when the problem occurred intermittently. Any thoughts....could it still be the neutral safety switch?

Regards,

Bob

Try pushing the shifter forward hard (while in Park). Try and crank the car while you are pushing the shifter forward. Could be the SB's or NSS (shifter bushings or Neutral Safety Switch).

In troubleshooting your brake/shut-off problem, determine the amount of vacuum coming from the top of the pump before you do or buy anything. IE: Troubleshoot from the pump to the firewall.

Check the main line and main line check valve for cracks when (and if) you remove it, to check vacuum on the pump. If you have a mighty vac., pull vacuum on the main line to be sure it is not cracked.

__________________
AJ

1985 300D (SOLD)

I have been having the same problems. The brake is very hard to push down, and then car doesn't turn off. Strange thing is that this is an intermittent problem. For the last week the problem has been gone, although it comes and goes. Get your problem fixed or your master cyclinder will be shot. After a few trips my brake pedal was going to the floor, and I wasn't stopping very fast.

I will be interested to see what you find out. I most likely have the same problem.

Is there any maintenance work to do on vaccuum pump if it is bad? There are a few different valves in the lines, are any of these sticking?

__________________
1983 300D Turbo, 150K

Got started today! First checked vacuum on line going into brake booster from the vacuum pump.........it had a very low reading around 10 Hg. I then went directly into the vacuum pump and the reading was basically the same. After several minutes the reading started to fluctuate going up as high as 22 Hg. When the reading went up to 22 Hg I reconnected the lines and checked the brakes which were now normal and the car shut off. This was short lived and the problem reappeared again.

Next I removed the vacuum check valve from the pump and the center was missing. Am I correct in assuming that I need a new vacuum check valve along with either a rebuilt or used vacuum pump. Could the missing check valve piece have caused the vacuum pump to malfunction?

Any suggestions and any good suppliers? I see some used pumps on Ebay for between $50 and $100.

Thanks,
Bob

What did you remove? I looked and don't see where a check valve would be?

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1983 300D Turbo, 150K

You can get a rebuild kit for the pump and the check valve here on the site. Top of the page "Buy Parts". If you have any questions, contact Phil and he will help you out.

The rebuild kit contains seals and new check valves for the inside of the pump. I rebuilt mine "on the car" (I did not need to remove it).

__________________
AJ

1985 300D (SOLD)

Erickson,

The check valve is on the top of the vacuum pump right where the vacuum hose is connected.

Hi all,

I ordered a rebuilt vacuum pump yesterday and have been soaking the hex bolts on the old vacuum pump w/WD40 because they are not budging. I am sure it's the original pump. Any hints on how to remove them?

This morning I decided to check the vacuum again and the reading at the pump was between 22-24 Hg, the car shut off with the key and the brakes were normal. I didn't take it out but tested it in my yard and checked it throughout the day and it never lost vacuum.

Is it normal for the vacuum pump to intermittently work or does it usually just stop working? The check valve on the pump was definitely defective when I removed it.

Thanks again,

Bob

It's normal to have a bad check valve. I'd just replace the check valve.

__________________
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

Good morning all,

I did some more computer research last night regarding the intermittent vacuum and vacuum check valve. As suggested by some my problem could be just the vacuum pump check valve.

When I took the check valve off, you could see straight through, the pieces were missing. Since the pieces have to be somewhere one suggestion was to fish out the pieces from the pump opening. They could be blocking the vacuum opening occasionally and causing the intermittent problem. To my surprise using q-tips and a wire I was able to locate two small pieces one being a spring and the other a tiny metal plate similar to the mercedes star.

I am still carefully fishing for more........does anyone know if those are the only pieces in the check valve? If so I can stop looking install a new check valve and report back.

I think we are getting closer and I might be sending back the pump when it arrives!.

Bob