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740 Trunk Lock Confusion

daniels740

Member
Joined
May 8, 2019
Location
South Florida
On my '89 740 sedan, with power locks controlled by the driver door, the trunk is never unlocked when I unlock the doors, but it always locks along with the doors if I had unlocked it earlier using my key. What's to blame and how do I fix it? Thanks.
 
On my '89 740 sedan, with power locks controlled by the driver door, the trunk is never unlocked when I unlock the doors, but it always locks along with the doors if I had unlocked it earlier using my key. What's to blame and how do I fix it? Thanks.

If it is anything like the trunk's central locking on the 86-93 240, it just can't get moving in the cold weather.
 
If it is anything like the trunk's central locking on the 86-93 240, it just can't get moving in the cold weather.
I really don't think it's that; I'm in south Florida and I dont know if 75 degrees is cold enough to cause any problems :rofl:. Jokes aside, the lock has been this way for a pretty long time now.
I just felt like it finally got to me today when I had to take the key out of the ignition to get something out the trunk.
 
I really don't think it's that; I'm in south Florida and I dont know if 75 degrees is cold enough to cause any problems :rofl:. Jokes aside, the lock has been this way for a pretty long time now.
I just felt like it finally got to me today when I had to take the key out of the ignition to get something out the trunk.
Make sure your trunk lock key slot is vertical. Pulling the key out when horizontal disconnects it from the central locking system. Not sure if it totally disables it, or just the unlock part. I'll go out and play with mine later.

https://volvornt.harte-hanks.com/manuals/1989/1989_740/89740_02.htm#pg37
pg37b.jpg
 
Make sure your trunk lock key slot is vertical. Pulling the key out when horizontal disconnects it from the central locking system. Not sure if it totally disables it, or just the unlock part. I'll go out and play with mine later.

https://volvornt.harte-hanks.com/manuals/1989/1989_740/89740_02.htm#pg37
pg37b.jpg
I always keep it vertical, but who knows, that might be the problem! I'll fiddle with it and try taking out my key when it's horizontal but I doubt It'll do the trick.
 
Those are the same valet key instructions for the 240 lock, so I think they both are similar. If you pull the key horizontal, you definitely won't be able to unlock the trunk with the central locking.

Our cars would begin to have your symptom (central locking will lock the trunk but not unlock it) around this time of year before the sun is up, but after the sun warms things back there, the lock motor has enough oomph to unlock it again. Maybe if I didn't tend to them it would act up on a cold, 75F Florida morning eventually.

door735.jpg


door3092.jpg


door3101.jpg
 
Could be a bent pushrod, loose lock motor, worn bushing, etc...
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trunklock.jpg

As long as it locks 100% of the time I think these can't really be the issue. Also, temperature has not affected the lock whatsoever, even when it was summer, at 90?, the lock still had this problem. I guess I could still give it a good cleaning and greasing nonetheless.
 
This thread has convinced me to lubricate my trunk locks too. When I lock my car from the drivers door, the trunk lock is always the last lock to chunk. Hopefully I can speed it up with some lubrication.
 
I think the lube helps at any temperature, but when it gets cold, the sclerosis in the aged rubber boot over the actuator provides a lot of extra resistance.

lock423.jpg
 
I'd venture to say make sure the key lock is in the proper position as previously mentioned.

I got it unlocking again by giving the lock a couple sprays with lithium grease while turning the lock with the key. I also opened and greased up the lock motor just to play it safe.
 
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