On the topic of door locks....

[Tomas7]

My 76 280C's passenger door only locks sometimes, after the car's been running.
Isn't my trunk supposed to lock as well? It doesn't.
What do I need to check, isn't there a valve somewhere that's acting up?

Thank you very much.

[Mike D]

Uggh, the dreaded coupe` vacuum lock problems. Makes me twitch every time I have to go through it.

First, there is a vacuum reservoir INSIDE the right front fender. This is supplied by a line from the manifold or carburetor depending on year and engine options. The line leads from there back across the firewall and into the cabin. It "tee's" below the brake booster. One leg leads inside the cabin and the other feeds the door lock mechanisms.

This is the large-ish hard plastic line you'll see when the doors are open. This supplies the vacuum to operate the key/trunk locks by separate return lines.

The cabin line supplies the diaphragms used for the A/C switch-over and the two diaphragms mounted below the seats which lock the tilt feature of the front seats. The seat locks are automatically applied when engine vacuum is present. The tilt lock is over-ridden by pressing the buttons mounted in the side panels in the rear so you can tilt the seat while the car is running.

Why M-B decided to use vacuum to operate the tilt feature instead of a simple manual latch mechanism is something only the engineers at Daimler understand.

There are check valves located in the locking mechanism lines but not in the tilt diaphragms or the change-over lines (I might be wrong on the change-over lines).

A Mitey-vac is your friend when it comes to tracking down these problems. Nothing very complicated. Usually just a matter of cleaning, lubing and replacing small bits of rubber lines which have dried out and split.

Have fun!

[Tomas7]

Originally Posted by Mike D

Uggh, the dreaded coupe` vacuum lock problems. Makes me twitch every time I have to go through it.

First, there is a vacuum reservoir INSIDE the right front fender. This is supplied by a line from the manifold or carburetor depending on year and engine options. The line leads from there back across the firewall and into the cabin. It "tee's" below the brake booster. One leg leads inside the cabin and the other feeds the door lock mechanisms.

This is the large-ish hard plastic line you'll see when the doors are open. This supplies the vacuum to operate the key/trunk locks by separate return lines.

The cabin line supplies the diaphragms used for the A/C switch-over and the two diaphragms mounted below the seats which lock the tilt feature of the front seats. The seat locks are automatically applied when engine vacuum is present. The tilt lock is over-ridden by pressing the buttons mounted in the side panels in the rear so you can tilt the seat while the car is running.

Why M-B decided to use vacuum to operate the tilt feature instead of a simple manual latch mechanism is something only the engineers at Daimler understand.

There are check valves located in the locking mechanism lines but not in the tilt diaphragms or the change-over lines (I might be wrong on the change-over lines).

A Mitey-vac is your friend when it comes to tracking down these problems. Nothing very complicated. Usually just a matter of cleaning, lubing and replacing small bits of rubber lines which have dried out and split.

Have fun!

Sounds like a good way to spend a Saturday, chasing down vacuum leaks and lines.
Thanks MikeD.

[optimusprime]

Tomas Yes as above your spot on .

[Tomas7]

Originally Posted by optimusprime

Tomas Yes as above your spot on .

Thank you very much optimusprime.