I've got some questions about the central locking on my 79 450SE, as it only seems to hold enough vacuum for 3 locks and unlocks after the car is stopped. Is this normal for a 40 year old W116?
I have tested elements of the system and have some other observations that may help
- If I don't lock the car, I still have vacuum for weeks, as I found out when working on passenger front door, disconnected the lines after a 2 weeks of car being stationary and heard a gush of air when removing lines
- If I don't lock the car, I can come back 24-48 hours later and successfully lock all doors
- Rear drivers door actuator seems to be a bit lazy compared to the other doors, even with vacuum this door is slower to lock and unlock than the other three doors.
- When I unlock the drivers door, there is a gush of air that emirates from the end of the master door actuator, it's audible to the point that you can hear it when the door trim is on
- Tested three vacuum lines in drives door y/r holds pressure, y/g holds pressure, but middle yellow line leaks very slowly
- Tested both blue one way valves in engine bay, both hold pressure.
Thanks in advance, keen to hear feedback
Nick
My car holds vacuum for months on end, but it has every part of the vacuum system renewed and resealed.
Based on the description, I'd say the master central lock cylinder in your driver's door is leaking. Quite a common issue. They were still available new not long ago, but are NLA now. There are aftermarket ones from VDO for about $50. Search for A1168000473 (OEM) or 248049004001C (aftermarket VDO).
Another thing to check is the rear reservoir seal. It gets hard with age, and starts leaking around the hard-line.
Then there's the actuator membranes, which can develop cracks as they age, and all the rubber connector and junction pieces.
Thanks for the feedback. I've ordered a new VDO master central lock cylinder and will replace all the actuator membranes (already replaced the four in rear door drivers side door). Although the rubbers looked ok, it's an easy task to replace.
Once I've changes master central lock cylinder and all actuators, I'll retest the whole system with a vacuum pump.
All
Received all the parts, actuator membranes (for all doors), master switch, but yet to troubleshoot and replace parts. From what I can tell, I've got a small leak from the master line into drivers door. When I pull hose off and connect it to pressure pump, I can see pressure slowly being lost. I've checked for cracks in reservoir seal, but looks good, how should I begin to troubleshoot this leak (Note, I've tested both blue one way valves in engine bay, both hold pressure)?
Thanks in advance.
If the leak is coming from the drivers door I would bet its the master "valve" in the door. They seem to wear out and leak predictably. Remove the door panel and you will be able to readily check the valve with your vacuum pump. You can check each line independently with the panel off and confirm that its the valve.
Thanks Jed.
Today I replaced master switch, but still no joy, so launched into some troubleshooting. Connected my vacuum pump (using a T piece to the expansion tank). This holds vacuum perfectly when no unlocking/locking is occurring, but as soon as I lock and unlock I lose vacuum, to the point where all vacuum is lost after 4-5 locks/unlocks. I seem to lose 40mm/Hg for every lock/unlock and visa versa.
I've replaced actuators in passenger door (drivers side), but still need to replace all other actuators. I assume it's highly likely to be a torn actuator somewhere in the system?
Don't rule out perforated vacuum lines in between the doors and the "A" and "B" pillars. Even under the rear seat I've seen lines break. Though, follow your advice about replacing the remaining actuators first.
I'm still yet to replace the other actuators, but after car has been standing for a week (unlocked), there's still a heap of vacuum, so I only lose vacuum when unlocking/locking. Hopefully will get round to changing actuators in next few weeks.
so how many lock unlock cycles is normal in a competent system?
4-5 doesn't seem unreasonable does it?
so how many lock unlock cycles is normal in a competent system?
4-5 doesn't seem unreasonable does it?
I'd check, but after standing idle since September it no longer has any vacuum left. That's new...
But 5+ should be easy in a healthy system.
4-5 sounds about right.
Just checked proper. I can get 5 full cycles on my car, and a very slow sixth half-cycle. That's with every part of the system having been replaced in 2016.
Well, you're supposed to lose vacuum as you operate the system with the engine off. Unless the engine is running there is nothing to replenish the vacuum supply in the reservoir. However, and as the others have stated, you should be able to operate the system 4-6 times with nothing but the vacuum supply in the reservoir. It's not uncommon to lose vacuum as the car sits, either. It should take a while, but how long? Anybody's guess is as good as mine. It depends on the tightness of the system.
I may be just lucky but I live in a place where we hardly ever lock our cars even at home. When I'm out in the Mercedes, I do "pretend to" lock it with the key sometimes and two and a half doors lock sort of. The boot does lock for some reason. I don't worry and go and do the shopping or whatever it is. I will get around to fixing this one day. Who is going to try and steal these cars anyway?
I had a cracked hard line in the driver's side A pillar. I cut it and spliced it with some spare rubber hose . With leaky diaphragms I get 2-3 cycles having just run the car.
Trying to steal a W116 would not be easy, I certainly agree.
Tim