R107 central locking is a vacuum system, not a modern electric actuator network. Soft locks, one door that never listens, or a pump that runs forever usually means leaks or a tired pump in the trunk area.
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Problems hub: common problems.
How the vacuum lock system works
A vacuum pump builds vacuum. Door elements, trunk, and fuel door use that vacuum to lock and unlock. Any leak collapses available vacuum so the pump runs long or locks move halfway.
Pump location
Typically in the trunk / battery region. Listen when you lock from the driver’s door: a healthy system pumps briefly then stops. Constant running means a leak or a pump that cannot build vacuum.
Leak testing
- Does the pump run — never, always, or briefly?
- Use a hand vacuum pump on individual door elements
- Inspect cracked tees and lines under carpets and along sills
- Test trunk and fuel-flap circuits separately if doors work
Fixes
- Replace cracked vacuum line (buy bulk line of the correct diameter)
- Replace leaking door elements
- Replace a weak pump
- Repair damaged connectors at the pump
Patience finds the last leak after the obvious ones. Smoke tests help on stubborn cars.
Details that finish this topic
How the vacuum pump system works
On an R107 this means verifying the condition on your year/engine before ordering parts. When in doubt, match the data card and engine number, then confirm with a specialist who works on 107s regularly.
pump location
Exact locations vary by year and market. Use a diagram for your chassis, photograph connectors before removal, and do not rely on a single forum photo from a different model year.
testing for leaks
Work methodically: reproduce the symptom, check power/fuses/relays, measure before replacing, then retest the same conditions (cold vs hot, loaded vs idle) after the repair.
door/trunk/fuel flap elements
fixes
When only one door fails
That usually points to that door’s vacuum element or the line serving it — not a total pump failure. Test elements individually with a hand pump before you replace the pump “just in case.”
