W124 rear door locking
 

My W124 was built in 04/90 and so has the first version central locking. The rear locks will not lock by either of the front door keys but can be manually locked. The fuel door and trunk lock fine. The vacuum pump runs for what seems like quite a long time but eventually shuts off. On opening the car, all door locks function normally if maybe a bit more slowly than before.

In starting to trace vacuum lines at the LR door, it looks like the vacuum line has been replaced because what's there is a 3/8 OD rubber hose while the lines at the pump are 5mm OD of a hard yellow plastic. Then the line disappears into the door post and I have no idea where it goes.

Would appreciate your thoughts. If I have to trace vacuum lines how does one get at them? Do I have to remove the seats, rugs, various trim? Can I get at the lines from underneath?

If I delay doing this or ignore it will the pump suck up trash and fail?

Thanks a lot.

John

I think the pump shuts off automatically to prevent excessive wear. The most common failure of vac lines occurs inside the rubber accordion(s) which are located between the door hinges. If the accordion is damaged or has separated from the door you can bet that's the problem.

I sections of a vac line can be replaced using rubber hoses which can be ordered here or elsewhere in the internet.



Learn to use the DYI section of this forum if you want complete information quickly. There you get the best of all the information that's been collected here. I know it's a pita to wade through but if you're going to repair and maintain your MB being familiar with our DYI forum is the quickest way to go.

I do not know the 124 but if it is like the 126, you will find a junction box under the carpet in front of the passenger front seat. There the hard plastic tubing goes to all the doors, trunk, and gas door. Hook up the mityvac there and trace your leak. Chances are that the actuator in the rear door is bad. New ones are not expensive and it is an easy replacement. Just be careful removing the door card and do not break off the plastic keepers; lift it up and then out to remove.

John, recommend buying whatever hose or tubing you may need from your local MB dealer. Their prices are somewhat high, but the items will be far more durable than those acquired at a Home Depot or an auto parts store.

Thanks for your reply.
On the W124, only AC air distribution and electrical harnesses are found under the front passenger carpet. I think I will have to take out the passenger seat or maybe both.

Which mityvac part number would work for checking vacuum lines? The only ones I've seen are for fluid pickup.