Bentley Arnage Project - Door Lock Actuators

I decided that the first job I should do on the 1998 Arnage was to sort out the central locking, keeping my baby safe seemed to me to be rather important. I knew when I bought it that the locking wasn't working, the seller - Mike - had been completely up front about it. The only lock that was working was the driver's door and even that wasn't reliable, Mike had taken the rear nearside door apart to have a look but when it came to me that was still not working so I decided it made sense to tackle that one first. At least that was the plan but the remote bit not working made my life difficult so I decided to look in to that first.

I have a tester that allows me to check the 433 MHz output from radio based remotes, I was getting a very weak and unreliable signal from my key fob. I thought it was probably the battery so opened up the case - single screw, easy job - and tested it with my meter. It's a  miniature 12v item, it was showing 12.4v at idle and 11.7 when transmitting - good. All it needed was the contacts cleaning, with that done it was now working much better - I like free fixes.

That done I went back to the actuator, which required removal from the vehicle. As Mike had already taken all the trim off it was just a matter of releasing all the control rods, removing the 3 6mm Allen headed bolts and withdrawing the lock through the generously sized hoe in the door. That enabled me to get at the two electrical connectors, once they were off I took the complete mechanism in to my workshop for further investigation.

These units use a rather small electric motor and quite complicated system of levers to make the thing work, they are covered in grease so you need plenty of rag and some solvent if you plan to work on one. Everything looked fairly free, you have to remove a black plastic cover before you can get at anything, it just pops off, it's fairly obvious. To get at the motor and gears you need to remove the white plastic cover, before you can do that you need to take off the actuator arm, its held on with a single small philips screw, again fairly obvious. There are then half a dozen screws that hold on the cover, with those removed the cover can be withdrawn, it can be a bit tight where the spindle exits, there is an o ring there to keep moisture out. You can now get at the motor, a cheap looking weedy thing that you might expect to find in a cheap Chinese toy. To be fair the whole mechanism really doesn't look anything like it's worth the £1100 (as of June 2026) that Bentley charge for a new one. Anyway, I digress, this is where the problem is, the commutator on that motor gets well dirty and needs cleaning. My weapon of choice was some high quality aerosol cleaner. It's lazy but taking these motors apart is a bit hit and miss, it can be a real pain to get them back together, it's always worth cleaning them first. I squirted plenty of fluid in there, spun it up on my 12v bench supply, rinse and repeat, I did it 3 times overall. Just by feel and sound I could tell the motor was now spinning much faster and more powerful than before. It was actually a lot more torquey than I expected. Regrease with some high quality dielectric grease - I use Dow Corning stuff, it's the best I have ever found.

Put it all back together, it's now ready to go back in the car, having not taken it apart I had to work out how it all went, although Mike had given me some guidance on that so I knew where it all went. I tested it before putting the trim panel back on, I didn't fancy having to remove it all again if it wasn't right - a few words of advice here. Before you start order some of the fir tree panel clips, you will need some. There are about 10 on each door panel, they will break either as you remove them or when you try to refit them. You have a choice - a couple of quid each from Bentley specialist suppliers or buy 10 off ebay / Amazon for 3 quid. I would also suggest getting at least a couple of the little plastic retainers for the control rods - there are two sizes 3mm and 4mm that could be needed. Same thing again price wise, I had to buy 100 but they cost just  bit more than a single one from Bentley. I broke one, the back doors are not too bad but the fronts are an absolute bugger to get at, largely due to the window glass runner being in the way. It's so frustrating when such a small thing holds you up, it's well worth having a couple on hand.

Anyway it worked perfectly, I was well chuffed. It all went back together quite easily, be sure to replace any cable ties you may have had to cut to get things apart, you don't want any wires trapped when the window goes up and down.

Now supercharged with confidence I set about repeating the trick on the front passenger side door - different kettle of fish altogether. The problem is in the rear door there is a big access hole right near the mechanism, no such luxury when it comes to the front door, which makes no sense whatsoever. Getting at the control rods and their retainers is an absolute sod, you can't see what you are doing and have to rely on feel and witchcraft to get them apart. It is doable though and once you have done it once the next time is a lot easier. The locks are pretty much identical in how they look and work, with the second one fixed you can reward yourself with beer, knowing that with 2 doors done you have saved yourself about 3 grand with the labour and parts costs. A tin of spray switch / contact cleaner is less than a fiver, it took me less than 3 hours to strip the door, repair the lock and put it back together, I would have done it in 2 if hadn't been so hot, I had to keep stopping to rehydrate.

You can buy new motors if you prefer, they are a tenner delivered, they seem to be used in numerous applications, there are two types available, so make sure you get the right one, the difference is in the brass gear pressed on to the spindle, make sure you order the right one. Be sure to do the bit with the 12v when the contact cleaner is still wet, it won't go alight but it will help dissolve and remove the carbon build up on the commutator, which is what reduces the efficiency of the motor.

I am not saying this is the only problem these mechanisms can have, I'm not saying it will fix your door lock but I can say with certainty that it fixed mine. I hope it works for you, these wonderful cars need to be maintained but the price of some parts is both inexplicable and unreasonable, 4 door locks would be over 5 grand supply and install but you could probably do all 4 in a day at a cost of a fiver as long as you have the right attitude and aptitude. I hope this helps somebody, if it does please drop a fiver in a charity box of your choice next time you see one.