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Changes to Mercedes W123 Vacuum Lock System Diagnosis Technique Introduction

Edit by Nicolas Siemsen

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Introduction
The door lock system on a W123 is controlled entirely by vacuum. It is a system made of many parts and can be complicated to diagnose properly if you've never done it before, and especially if the system has been left to deteriorate for some time. [ … ] The first step to fixing the system is to properly diagnose it. Vacuum components, such as door and trunk lock actuators, can be quite expensive so replacing only those that need it will save you time and money over throwing parts at the system in an effort to fix it. [ … ] This guide will walk you through diagnosis of the vacuum door lock system on an early style W123 with the four diaphragm door lock vacuum actuators. However, the technique applies to later models as well; the actuators work the same despite looking different. [ … ] NoteAs the guide progresses, you may consider replacing all of the "Y" and "X" connectors for the lock system since you will be disconnecting most of the hard plastic lines from them anyway. Old rubber connectors can sometimes swell around the hard plastic lines and no longer hold a tight vacuum. This might lead to very slow leaks, but leaks nonetheless. New ones are inexpensive and can help create a very tight system along with repairs to any leaking actuators or cracked hard lines. [ ] Note - if you find that part of your leak is due to old and cracked diaphragms on your early style door lock vacuum actuators, see the repair [guide|20147|repair guide under the Mercedes W123 repair section section] to learn how to fix these without replacing the entire assembly.
The door lock system on a W123 is controlled entirely by vacuum. It is a system made of many parts and can be complicated to diagnose properly if you've never done it before, and especially if the system has been left to deteriorate for some time. [ … ] The first step to fixing the system is to properly diagnose it. Vacuum components, such as door and trunk lock actuators, can be quite expensive so replacing only those that need it will save you time and money over throwing parts at the system in an effort to fix it. [ … ] This guide will walk you through diagnosis of the vacuum door lock system on an early style W123 with the four diaphragm door lock vacuum actuators. However, the technique applies to later models as well; the actuators work the same despite looking different. [ … ] NoteAs the guide progresses, you may consider replacing all of the "Y" and "X" connectors for the lock system since you will be disconnecting most of the hard plastic lines from them anyway. Old rubber connectors can sometimes swell around the hard plastic lines and no longer hold a tight vacuum. This might lead to very slow leaks, but leaks nonetheless. New ones are inexpensive and can help create a very tight system along with repairs to any leaking actuators or cracked hard lines. [ ] Note - if you find that part of your leak is due to old and cracked diaphragms on your early style door lock vacuum actuators, see the repair [guide|20147|repair guide under the Mercedes W123 repair section section] to learn how to fix these without replacing the entire assembly.

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