On a 1965 S-type, the rear door opens one slot when driving on less than perfectly flat roads, even though the door is locked.
What is the cure here please?
Clean and lube the mechanism, especially on the inside of the door, if that doesn’t fix it move the catch a wee bit outwards.
Did you recently change door seals?
Fairly new seals, but I have had this problem off and on since 1985.
But I can´t understand why it jumps open one slot, even though the door is locked…
It’s a two stage latch. When the mechanism is worn, the ratchet on the second position can slip out, especially when the seal prevents the door from moving far enough in to get a positive action on the pawl.
EDIT: iirc all the lock does is make the button miss moving the pawl - IOW, latching has nothing to do with locking.
Ok, and thanks Andrew.
So I should really get another lock assembly, which hopefully is less worn…?!
Try with cleaning and lubing the door side mechanism, you never know.
I drilled the staking out of a Mark 2 mechanism once - it’s a world of jiggery pokery, so if you can get ones which are new or less worn then that’s the easier solution.
Or how about a drop of LocTite where the outside part, visible with the door open, enters the interior of the door?
Loctite, on a door catch?
I know, it sounds stupid, but in an attempt to stop that turning bit from opening so easily…
Anyway, I had a look at the part that´s mounted on the body (latch?), and underneath there is a sliding part with a spring. On the normally operating door, that sliding bit is fixed in the innermost position, but on the faulty door, it slides out a few mm. Fairly easily pushed back with a finger. I.e. it will move when opening the door a few times. I wonder if that could be the culprit…