W123 Vacuum Assistance - PeachParts Mercedes-Benz Forum

RoysVeggy · #1 11-13-2008, 05:41 PM

A while back, I located a few threads where members assisted with a step by step help guide. Needless to say, I could not find it again. Would you guys be willing to assist my vacuum endeavors?

As stated, where should I start in the engine bay with testing for vacuum leaks? Brake booster? I am excited to test what you guys say and come back with results to move onto the next step. Thanks in advance for your help.

Chad300tdt · #2 11-13-2008, 05:45 PM

You can start with testing the vacuum pump to see if you're pulling enough vacuum. Then work through the vac tree from there eliminating branches.

You should share what your vac issues are that you're aware of. Central locks, brakes, delayed shutdown?

RoysVeggy · #3 11-13-2008, 05:51 PM

Chad,

I believe everything in the engine bay is ok. I will still test all of the lines.

One day, the car would not shut off. After disconnecting the Door Locks, the car was able to shut off, so I know there is a vacuum leak somewhere in the door lock assembly.

Should I test the Master Vacuum element in the drivers side door? Is that normally a culprit? To test the vacuum pump, do I hook up to the Brake booster? Which nipple? What should it pull when the car starts?

Chad300tdt · #4 11-13-2008, 06:06 PM

You can test the vacuum at the yellow check valve or at one of the lines that go to the brake booster vac line. Just pull one off while the car is running and verify it's sucking. Then put a vac gauge on the line and verify you're getting 18-23 inches.

With the central locks, start by testing at the check valve. The yellow with black or blue stripe leads to the vacuum reservoir. The solid yellow leads to the driver door master switch. If your reservoir is good (they usually are fine), test the solid yellow line with the doors locked and unlocked. That will narrow down which side of the vacuum is leaking. Then move to under the driver floor and test the lines there. There is a yellow with green stripe and a yellow with red stripe. They run into "Y" connectors that branch the lines. One set runs to the rear driver side door, the other runs to the passenger side where it branches under the floor on that side. On the passenger side it branches to the front passenger door, the rear passenger door, and the third goes to the fuel door and trunk or hatch.

Once you find where your leak is coming from you can worry about taking off a door panel if needed. You may have leaks in the rubber vacuum connectors that make the branches or the ones that transition from the hard vac lines to the actuators in the doors. You could also have a leak in a diaphram in one of the actuators.

EDIT: It should be pretty easy to locate the leak since it was large enough to cause delayed shutdown. It's more of a hassle when the leak is a small, slow one.