Central Locking Diagnosis

[Aaron]

Can anybody give em any pointers in an attempt to locate the fault with the central locking on my 1978 300D(123)?

I dont know very much about how this system works other than it is vacuum based and the vacuum is generated from a pump which also provides vacuum for the brakes. As a result of my very limited knowledge, all I have been able to do is check that there is vacuum at the three way distributor near the brake servo and that is about it.

Thanks in Advance

Aaron

[Aaron]

I forgot to mention, the problem is that the system is totally dead and hasn't worked since I have had the car.

[robnelson200]

I had a problem where the C/L on my '88 W124 260E died, and it turned out to be a burnt out motor in the vacuum generator (Which was located under the offside rear seat). It's worth having a poke around and see if the control unit / vacuum generator is working. The one in the W124 is mounted in sound deadening foam and contains a motor, vacuum storage unit and vacuum feed pipes... IIRC the three way distributor in the engine bay is not related to the C/L.


If that seems OK then it would appear to me as if there's a break in one of the vacuum feed hoses running throughout the car to the door locks...

I can't be of much more specific help as I didn't have C/L on my W123 230TE (I did have leather seats though!!)

Oh, one other point stikes me - if the vacuum feeds are OK it is possible that there is one "sticky" door lock which the vacuum can't unlock and this would (does on the W124) cause other doors not to be unlocked.

Rob.

[TimN]

Sounds as though your vehicle operates its c/l from a vacuum created by the vacuum pump for the brakes. This is located on the front of the engine and is chain driven. If this had failed then the performance of the brakes would be severely affected.

If the system does not work at all (Try revving the vehicle and simulataneously unlockin/locking to see it works which should get it to work even with a leak in the system) then it is most likely disconnected. Possibly at the drivers door lock, vacuum resevoir, under the rear or under the bonnet. Also just check to see if the towing positions of the lights dip/raise when adjusted as they are on a parrelel vacuum system. Try thes ideas and come back to me

[Andy]

Hi Aarron,


I have written a quite an indepth description of how to test the central locking on your 123. Have a look through previous posts.


Regards

Andy @ www.mercedesservicing.com

PS. 123's central locking works completely different to the 124's

[jaymanek]

Hi,

I would read andys report. There are no electrics involved. Mines a 1980 and i have stripped it from front to back.
Common areas for leakes are, 1) In the boot, theres a container above the petrol tank which holds the vaccuum, check for leaks there. 2) Boot lock, the vaccuum operation has some rubber parts here which are bound to be falling to bits and hence leaking. 3) petrol flap has the similar thing as boot (accessed from inside the boot). 4) Under Steering column inside car, theres a white one way regulator, this should only pass air one way, take it off, blow through one end at a time, and if you can blow air through from both ends, then buy a new one. Theres a similar thing under the bonnet, just before the pipes feed to the inside of the car, check this (should be a yellow one). It takes a while to check all the different things im afraid :(

Have Fun!

Jay