Author Topic: Central locking troubleshooting and repair  (Read 975 times)

raueda1

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Central locking troubleshooting and repair
« on: 08 April 2021, 10:24 AM »
Mine no longer holds overnight so it's time to fix it.  I've got the manual and will be reading and rereading.  The system seems only slightly less complex than the fuel injection.   I did search here but didn't find all that much.  So here are a few general questions:

Tips, Tricks and Techniques:  Anything special secrets that aren't in the manual?

Tools and equipment:  I've got a vacuum pump (for AC systems), vac gauge and countless Y's, T's, connectors and spare tubes.  Will I need anything else?

Typical failure patterns and what to replace:  Do the system elements tend to fail at the same time?  If, for example, an actuator is no good, does it make sense to change them all?

Rubber accordion in door:  The old ones are cracked but I seem to have new spares.  Seems like a good time to replace them.  Can this be done with the door on?  I'm assuming that all the tubing and wires can be disconnected inside the door and the new accordion slid along the bundle and out the hole in the door.  Is this reasonable or even possible?

Other stuff while the door is apart?  The driver's window is a bit sluggish so I'll try to take that up as well.  Anything else to do while I'm in there?

Trying not to reinvent the wheel here.  Thanks in advance for any info or tricks.  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Alec300SD

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Re: Central locking troubleshooting and repair
« Reply #1 on: 08 April 2021, 11:49 AM »
Mine no longer holds overnight so it's time to fix it.  I've got the manual and will be reading and rereading.  The system seems only slightly less complex than the fuel injection.   I did search here but didn't find all that much.  So here are a few general questions:

Tips, Tricks and Techniques:  Anything special secrets that aren't in the manual?

Tools and equipment:  I've got a vacuum pump (for AC systems), vac gauge and countless Y's, T's, connectors and spare tubes.  Will I need anything else?

Typical failure patterns and what to replace:  Do the system elements tend to fail at the same time?  If, for example, an actuator is no good, does it make sense to change them all?

Rubber accordion in door:  The old ones are cracked but I seem to have new spares.  Seems like a good time to replace them.  Can this be done with the door on?  I'm assuming that all the tubing and wires can be disconnected inside the door and the new accordion slid along the bundle and out the hole in the door.  Is this reasonable or even possible?

Other stuff while the door is apart?  The driver's window is a bit sluggish so I'll try to take that up as well.  Anything else to do while I'm in there?

Trying not to reinvent the wheel here.  Thanks in advance for any info or tricks.  Cheers,
Tools and equipment: 
Spare check valve(s).

Rubber accordion in door:   
http://www.peachparts.com/shopforum/diesel-discussion/362539-diy-pictorial-replacing-rubber-boots-cabin-door.html

Other stuff while door is apart:
http://www.peachparts.com/shopforum/diesel-discussion/399670-w116-door-check-maintenance-repair.html
Check and lubricate window regulators & window guides.
Replace interior and exterior rubber window weatherstrip/wipers if cracked.
Make sure drain holes in bottom of doors are free flowing.

79 W116 300SD 'Stormcloud' new as of 10/22/2017
78 W116 300SD 'Desert Rose' new as of 01/26/2014
83 W126 300SD 'Rena 2.0' with engine from 82 W126 300SD Rena' (SOLD and crushed 11-20-2017)

ptashek

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Re: Central locking troubleshooting and repair
« Reply #2 on: 08 April 2021, 11:59 AM »
Tips, Tricks and Techniques:  Anything special secrets that aren't in the manual?

- a common, but rarely mentioned source of leaks is the rear reservoir grommet through which the hardline enters the tank

Quote
Tools and equipment:  I've got a vacuum pump (for AC systems), vac gauge and countless Y's, T's, connectors and spare tubes.  Will I need anything else?

- patience ;D

Quote
Typical failure patterns and what to replace:  Do the system elements tend to fail at the same time?  If, for example, an actuator is no good, does it make sense to change them all?

- aside from the reservoir grommet, the master "vacuum switch" in the drivers door is the first suspect
- from own experience, if one actuator has cracked/leaking rubbers, they will all look more or less the same; replacing all is the best approach here

Quote
Rubber accordion in door:  The old ones are cracked but I seem to have new spares.  Seems like a good time to replace them.  Can this be done with the door on?  I'm assuming that all the tubing and wires can be disconnected inside the door and the new accordion slid along the bundle and out the hole in the door.  Is this reasonable or even possible?

- sounds like a plan, albeit I've replaced mine when the door was off so can't say for sure


Quote
Other stuff while the door is apart?  The driver's window is a bit sluggish so I'll try to take that up as well.  Anything else to do while I'm in there?


- check for rust at the bottom of the door; there's usually a ton of debris accumulated there as well
- lubricate door hinges (you'll need a grease gun to do that)
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

daantjie

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Re: Central locking troubleshooting and repair
« Reply #3 on: 08 April 2021, 12:39 PM »
Both Alec300SD and ptashek make great points here.
When door card is off this is a great time to clean, inspect and lube your window mechanisms, they are notorious for warping due to old/lack of grease.  This is dirty work but very satisfying to go the whole hog once you have the door cards off.  Also lube the latch mechanism and check the door pulls for easy action, very easy to lube all the pivot points once you have it all open.  I used my trusty Permatex Dialectric Grease liberally, great stuff.  You may also want to replace the plastic membranes, they are usually a bit crusty by now.  I just cut my own from thick, clear plastic, and sealed them back on.  It does make a difference to keep moisture out of the cabin.
« Last Edit: 08 April 2021, 01:10 PM by daantjie »
Daniel
1977 450 SEL 6.9 - Astralsilber

BCK1963

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Re: Central locking troubleshooting and repair
« Reply #4 on: 08 April 2021, 02:06 PM »
I think it looks and reads more complicated than it actually is.
If you test one actuator after another by taking off all unnecessary tubes and closing all openings, you will get a good result with the vacuum pump.
The more people you ask the more primary suspects you will get. If you find one membrane to be done, there is a good chance that the others will follow soon.
On my car the driver's door master vacuum switch and tank lid actuator were the ones.
With all tubes and wires removed you can change the accordion but fixing it in its place is a mess because typical human fingers are too thick and have too few links.

Good luck.
Bernd

1976 Merc 6.9  since 2013
1974 Caddy CdV   since 1992  (for sale)

rumb

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Re: Central locking troubleshooting and repair
« Reply #5 on: 08 April 2021, 05:40 PM »
The DIY link did not mention that the vac line is secured to the bottom of the door in the very front bottom corner and is a real B to get off.

Start at the drivers door and work your way around the car.

The exterior door handles are very easy to remove and greasing them makes them open like silk.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

raueda1

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Re: Central locking troubleshooting and repair
« Reply #6 on: 09 April 2021, 07:31 AM »
Thanks to all.  This is very helpful and fills in the blanks nicely.  Looks like I'll get started this weekend.  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

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Re: Central locking troubleshooting and repair
« Reply #7 on: 09 April 2021, 08:49 AM »
I realized that I have another question.  The vacuum diagram in the manual seems to show that there are several "Y's" and a check valve behind the firewall someplace under the dashboard.  Is this so?  I hate doing stuff under the footwells.  Picture of my setup under the hood is shown below. Sorry, not a great pic.  Thanks and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

revilla

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Re: Central locking troubleshooting and repair
« Reply #8 on: 09 April 2021, 09:41 AM »
Yes, there’s another check valve behind the dashboard between your steering wheel column and the A pillar.  It was smartly placed there to avoid someone opening the hood/bonnet and blowing air from the main vacuum lines that enter next to the fuse box to unlock/steal cars. I know of some people who have intentionally remove it to have a “plan B” to unlock the car if needed.
Additionally, for a complete diagnosis of the vacuum system we must check the lines and ‘Y’ rubber connectors that run from left towards the glovebox and to the right A pillar. There are a total, if I remember correctly, of 4 lines hidden there behind the center console and glovebox (red, green, yellow/green, yellow/red). The red and green control the heater valves. There’s also a diaphragm next to the hvac fan, but this one rarely fails as it isn’t exposed vertically as the elements inside the doors.
I always start with the check valves next to fuse box, then air switch in drivers’ door, then starting from the trunk lock, to the gas trap lock, then rear right door, then front right, then rear left door. The advantage of this approach is that you can test for leaks by section therefore ruling out those areas that are leak free, and working your way towards the vacuum source. 
What to look for? I have found many blocked check valves, broken diaphragms in each of the 3 doors that have them (99% culprits are the 2 top (total 4) that fail due to accumulating humidity, dust, etc that sits on top. Also broken plastic lines with very difficult to see hairline splits. Despite other accounts, I have personally never seen a failure in any of the rubber connectors, they seem quite robust, even the ones at the engine compartment due to heat.   But they are so easy to check that it worth the effort.
Last advice, always use vacuum to test as opposed to putting pressure in the lines as it might pop the diaphragms. Don’t ask me how I know that...
Good luck.
« Last Edit: 09 April 2021, 09:49 AM by revilla »
Robert
W116 1977 280SEL & 1979 280SE

raueda1

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Re: Central locking troubleshooting and repair
« Reply #9 on: 11 April 2021, 11:07 AM »
Yes, there’s another check valve behind the dashboard between your steering wheel column and the A pillar.  It was smartly placed there to avoid someone opening the hood/bonnet and blowing air from the main vacuum lines that enter next to the fuse box to unlock/steal cars. I know of some people who have intentionally remove it to have a “plan B” to unlock the car if needed.
>>>snip<<<
Outstanding, thanks!
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

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Re: Central locking troubleshooting and repair
« Reply #10 on: 11 April 2021, 02:48 PM »
Edit:
Oops, wait!  the stupidist question was easily answered.  Somehow I missed it.   ???  The manual has leakdown specs which somehow I missed.  I'll compare with my results.  Still, any wisdom is always nice.

-------------------------------------------------
OMG, I guess this must be the stupidest question ever posted, but here goes.   :o

When is a vacuum leak really a leak?  I've been trying to go through the process but it seems like everything leaks, at least to some small extent.  I'm using an electric vacuum pump and the usual manifold vac gauge.  The pump will pull about 23 in Hg / 60 cm Hg.

1. Does the vacuum on a given circuit need to hold, say, 99.9% overnight? 
2. Or is it "OK" if it just slowly drops over several hours? 
3. Or is it only a leak if the pump can't pull any vacuum at all (i.e, vacuum never gets to what the pump can pull and drops to zero immediately)?   

I'm seeing various examples of 2 and 3 but never 1.  Is 1 even possible ("nature abhors a vacuum")?   I have no experience or context here. Any wisdom appreciated.  Thanks and cheers,
« Last Edit: 11 April 2021, 02:53 PM by raueda1 »
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

BCK1963

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Re: Central locking troubleshooting and repair
« Reply #11 on: 12 April 2021, 09:38 AM »
I guess that there is no ultimate truth.
All components age with time and in particular the rubber lids of the actuators slowly become porous even if they 'feel' like still being flexible.
Given the reports of proud owners that their system still worked after several weeks and even months, your reading on the pump manometer should come close to 1. Please mind that you test single spots but the capacity of holding the vacuum is the sum of all individual spots.

I found my actuator for the gas tank lid being faulty and I cut it off. Now the system holds the vacuum for 3 - 4weeks which is ok for me.

If you want your vacuum system being as perfect as the appearance of your engine compartment ..... good luck :-)
Bernd

1976 Merc 6.9  since 2013
1974 Caddy CdV   since 1992  (for sale)

raueda1

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Re: Central locking troubleshooting and repair
« Reply #12 on: 12 April 2021, 05:32 PM »
I guess that there is no ultimate truth.
All components age with time and in particular the rubber lids of the actuators slowly become porous even if they 'feel' like still being flexible.
Given the reports of proud owners that their system still worked after several weeks and even months, your reading on the pump manometer should come close to 1. Please mind that you test single spots but the capacity of holding the vacuum is the sum of all individual spots.

I found my actuator for the gas tank lid being faulty and I cut it off. Now the system holds the vacuum for 3 - 4weeks which is ok for me.

If you want your vacuum system being as perfect as the appearance of your engine compartment ..... good luck :-)
LOL, it's not so hard to make the engine bay look good when the engine is out of the car.  But yeah, I take your point.  In any case, I did progress a bit and discovered that the door switch is entirely useless.  Regardless of the piston position there's leakage between the respective connections.  The system actually worked extremely well until it didn't.  It was a kind of overnight failure from "works perfectly" to "doesn't work at all."  So I guess the switch just completely let go.  My hope is that replacing it returns the system to what it was before.  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

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Re: Central locking troubleshooting and repair
« Reply #13 on: 14 April 2021, 09:27 AM »
OK, made some progress.  As usual it's 2 steps forward, one step back.

The good:  The door switch was totally inoperable as mentioned above.  New one is on order.  I further tested the locking system by pulling vacuum on the respective locking and unlocking lines on the switch.  The whole locking system works perfectly, no leaks whatever anywhere (doors, trunk, fuel flap).  This is great news and simplifies my life.  :D

The bad: The line to the trunk reservoir seems to leak.  This is the gray-yellow line that snakes from the engine compartment to the floor to the trunk.  It will have to be replaced. I envision a lot of tedious and annoying interior disassembly.   I'm envisioning the possibility of using the old tubing to pull the new tubing through, kind of like pulling wire through a wall with a fish-tape.  Maybe in several sections and connecting them.  Are there any shortcuts?  And is there any sense in trying to source the correctly colored tubing?  Keeping the right color would be a nice touch.

And the ugly: The other lines (gray-red,  green-yellow and blue-gray) control the heating.  The blue-grey goes to the front vac. reservoir and is OK.  Both of the others leak very fast, which I assume is bad.  Practically speaking this isn't necessarily the worst thing.  My heater core is disconnected cause of a small leak, so the heater doesn't work anyway.  But I don't drive the car when it's cold and the AC still blows sub-arctic cold.  Nevertheless, it would nice to fix it while I'm in there.  I'll look at the manual carefully, but any tips, tricks or comments would be terrific.

I'll report more when there's more to report.  Thanks for the help to this point and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

ptashek

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Re: Central locking troubleshooting and repair
« Reply #14 on: 14 April 2021, 10:23 AM »
The bad: The line to the trunk reservoir seems to leak.

I'm assuming you've plugged it at the reservoir end, before testing? Could be just the grommet otherwise.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)