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  #1  
Old 03-28-2016, 08:09 AM
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300td tailgate power locks, not unlocks

The tailgate in my 1984 300TD locks by vacuum, but doesn't unlock. I have to unlock it with the key.
It's not a vaccum leak, I can leave the car sitting for a few days locked or unlocked and there's still enough vacuum to do 4 or 5 lock/unlock cycles. When I unlock the doors, the trunk make a loud CLICK noise. With the inside panel of the tailgate removed I can see the vacuum piston moving if someone turns the key in the driver door, but it doesn't pop the lock.

The whole lock assembly is ridiculously tightly packed into the tailgate and I've been afraid to try and remove it, especially if there's an easy way to fix the problem WITHOUT removing that mess.

I should also note, turning the key in the tailgate is a bit stuff, takes more force than it probably should, I lubed the cylinder with graphite lube and sprayed the internal latch mechanism with silicone lube, it helped very slightly.

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Old 03-28-2016, 10:26 AM
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I was able to get much more snappy action on my 87 300TD by pulling the mechanism, cleaning, and re-lubricating.

Granted the 124 has an electrical assist for the latch and unlatch but it does also have the vacuum pod for lock and unlock. BTW if anyone does this to their 124 *watch your fingers* that motor will snap your finger clean off...

The FSM for the 123 should have the procedure for removing the latch assembly and adjustment.
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  #3  
Old 03-29-2016, 08:41 PM
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Is the vacuum door lock actuator on the rear hatch for a W123 300TD the same as the side doors? How do you access the actuator? Thanks.
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Old 03-29-2016, 08:43 PM
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Bump
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Old 03-29-2016, 08:50 PM
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I don't think it's the same as the door actuators, but you can access it by removing the inner fabric panel of the trunk lid. It's on the driver side tucked up into a space so tight no grown man can fit their hand.
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Old 03-29-2016, 08:59 PM
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Thanks.
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Old 04-05-2016, 06:47 AM
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Anyone?
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Old 04-05-2016, 08:59 AM
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I did that job years ago its not to bad. I may even have a spare actuator still kicking around.
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  #9  
Old 04-05-2016, 09:12 AM
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It's not the actuator, that works fine
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Old 04-05-2016, 07:34 PM
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Thumbs up sticky latch assemblies

I like to use transmission oil as a cleaning lubricant for all stiff or frozen parts like latches or side view mirrors. ATF has mild cleaning agents, and is designed to want to flow into every available nook and cranny. If you can get some in an eye dropper or something, you can dribble in onto the moving parts, and then lock and unlock it by hand to clean the joints. Don't use the key or you might bust it off in the tumbler! If you can't get to everything you might have to pull it and clean it properly, but I've had good luck with a carefully directed dribble of ATF. Good luck!
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Old 04-05-2016, 07:41 PM
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Yea not a bad idea. It's back down into the single digits again this week, hopefully it warms back up this weekend. I can use the key in the trunk if I go carefully back and forth it'll unlock.
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Old 04-05-2016, 09:22 PM
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I went through this myself a few years ago.

The vacuum actuator for the tailgate is different than the doors. The part number from the EPC is A 123 800 24 75.

My latch assembly was not very free moving and still isn't the best. Anything less than an optimal vacuum to the element would cause it not to cycle fully.

The big culprit in my case was the fuel door element. The plastic case was slightly bulged causing intermittent leak downs. I replaced it with a better used element and am getting more consistent lock/unlock action.

As noted in the other answers lubrication is important.
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  #13  
Old 04-06-2016, 05:09 PM
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There are zero leaks in the system. It can sit locked for two days (longest I've gone without driving it), and still have enough vacuum left to lock and unlock the doors 5 times.

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