Can't advise how to further strip down the lock (someone will be along later who does know!), but have you got your caravan level? I know this greatly affects whether my door and pop top roof work as they should.
Also, could it be the actual door (or maybe the frame) that is out of shape or misalligned in some way that would make the lock stiff? Has it always been like that, or has it gone that way over winter? Check the door seals as well where they go around the lock, in case a bit has turned the other way when you weren't looking!
I'd leave the WD40 to penetrate a bit before I tried taking the lock off... you may need something like 3 in 1 oil to loosen it if indeed it is the actual lock and not something like the above that is causing the problem.
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Is your van a recent purchase? The reason I ask is because when we first got our van an Abi of mature years the lock was very stiff and didn't improve with wd40. However as we have used the lock more frequently it has become looser and more easy to use. Just treat it gently to start.
We had the same problem but our dealer fixed ours under warranty, if you google Hartal you will see that is seems to be a common problem. There are also some suggestions on how to fix.
As Janette says Hartel had a problem like you describe, I had it on my van. The component parts were made slightly out of spec and are causing too much pressure/friction on the moving parts. Relatively easy fix, you can spray lubricant till the cows come home but it needs modifying to fix it permanently.
I am not 100% but I believe that WD40 contains not just lubricants but solvents too. Using it on metal will be fine. However used on certain plastics it can react with them and make the surface sticky. The opposite to what you require. It may be too late to fix but you could try silicone lubricant or certain furniture polish or the best would be a graphite grease. If I am wrong someone will correct me soon.
------------- A barman is just a pharmacist
with a limited inventory
you need to remove the cover with hartall written on it to get at 2 of the screws.
then you need to remove the green and red covers to get at the other 2. these are hard to get out, I used a very small screwdriver.
then you can take the lot off.
i got it all cleaned out, and then got a bit of sandpaper to polish the barell bit up a bit and gave it a good clean out, and have greased it all and put it back together. works fine now.
by the way watch the screws...2 are shorter....i found out to my detriment!!!!!
I had a the same problem ours is the hartel lock I stripped it down and eased the parts with wet n dry sandpaper I lubricated the parts with graphite powder instead of grease and it's been fine since
I wondered if there were any more screws underneath the red and green inserts. Didn't fancy levering them out causing possible damage in vain. Now I know I need to do so I will. Many thanks to ALL. The picture is just the ticket. Got some quality silicone grease and wet N dry so will fix it over the Easter.
Got to agree with Chalkie56 about WD40, I used it on my gas locker hinges and after a couple of days they were stiffer than before I used WDF40. I now use silicone spray on any hinges and locks, and have never hade any more problems.