PeachParts Mercedes-Benz Forum - View Single Post

Rick Miley · #3 01-12-2004, 10:04 AM

Ok, now let's address these things one at a time.

I have no experience with W123 automatic transmissions, so will just go with what Kerry said.

Regarding the brakes, inadequte vacuum will make the brake pedal harder to push down - nothing else. If that's not the symptom, then something else is wrong with the brakes and you need to explain in more detail what you mean by the pedal is "lower."

Using a MityVac to pull a vacuum on the main line won't tell you very much because it displaces a relatively small volume of air, while the brake booster and the door lock vacuum reservoir hold a lot of air. So you'll have to pump a long time with the MityVac to get anywhere, and if something leaks you won't know what it is.

The first test I would do is pull both the small connections for vacuum consumers from the main line. Block one of the ports using a rubber connector and a golf tee. Then connect the MityVac to the other port and start the engine. The engine driven vacuum pump should easily produce 20" or more of vacuum. If it doesn't then one of three thing is wrong:
1. The vacuum pump itself is broken.
2. The main line has a leak.
3. The brake booster has a leak.

Then you start chasing from there. I haven't been down that road, so I can't tell you how to disconnect the main line and connect the MityVac to the pump. Maybe somebody else can help or it will be obvious when you get there.

However, if the vacuum tests good there then you can go on. Shut the engine down and use the MityVac to test each of the circuits separately. If you find one that doesn't hold vacuum, then you start chasing. Lots of information is available here by using the search feature. I wrote a complete description of how the locks work a few months ago. You could find it by searching for "vacuum and locks" in this forum under my name.

Post back here if you still need help.