brunnhilde's broken key

Anything to do with automotive lock and key gets very expensive. Get a rusty nail and scratch these words on your windscreen: "never, ever, lose or break a key"

All my life I tried hard to avoid the service of tow truck, funeral home, and locksmith



Brunnhilde has a broken key inside the lock cylinder on the sliding door from the previous owner. Normally this is not a problem because of remote control locking system one seldom use the key to unlock the doors. However for water spots I had a chipped key made so I can carry it with me into the water. I have to use the key to open the doors and only recently I discovered I could not insert a key into the sliding door. It has a broken key stub inside. Unlocking the front doors using a dumb key does not unlock the sliding door so it is a major POTS as it is the most frequently access door when camping.

I took it to a locksmith and he spent over 1 hour extracting it to no avail. I told him I would remove the lock from the door and bring it in. He was quite confident that if I remove the lock he can get the key out. I found out yesterday he will be away for 2 weeks starting today.

Last night I remove the door handle together with the lock cylinder. I consider myself mechanically inclined so I want to give it a shot myself. I looked at the assembly and tried every conceivable way to extract the cylinder to no avail.

lock handle assemblies - lock cylinder held inside the right assembly (arrow points to y-shape actuator); I used the cable tie to compress the spring to make work easier.

I refer to the factory service manual and it says:

To remove the lock cylinder:
1) Remove the door handle (ref section xyz)
2) Remove the lock cylinder from the handle

Typical useless German shop manual so common today.

Upon close inspection I can see someone previously has tried and cause a superficial crack on the plastic by plying on a wrong spot hoping to release the cylinder. I now know I am just retracing all his steps up to the point he decided to live with the broken key in the sliding door lock.

I could see that the lock cylinder has a pin which the Y-shape plastic actuator of the unlatching mechanism attached to the metal pin of the lock tumbler. The Y-shape plastic actuator has a double barb designed to lock onto the cylinder pin's shoulder. To me it is very clear that the design intends the assembling of the two parts in the factory, but not to be separated in the field - hence unserviceable. To remove the lock cylinder one have to destroy the plastic barbs and buy a new handle assembly which comes with the Y-shape actuator.

arrow points to one of the two opening where you can see the plastic barbs

 

arrow points to pin of the lock cylinder installed into the y-shape actuator by 2 plastic barbs

Still undeterred, I drilled 2 small holes to try to insert a taper metal rod to pry out the barbs. In no time it confirm my fear that the barbs simply does not budge. I would estimate it requires a few tens of pound force during assembly.

I checked the cost of the door handle ~$25
I also checked the cost of the lock cylinder ~ $85

I proceeded to remove the cylinder by melting the plastic barbs with a soldering iron. It took a bit of struggle and I removed the lock cylinder.

drilling 2 holes to ply the barbs did not work

pieces parts after melting the barbs with soldering iron

From the hour long experience tried the extract the key we knew the key is wedged in there very tight - most likely due to the burr and deformation created when the key was broken. My locksmith told me once the cylinder is out he can remove the pins and springs and the key stub should come out.

Unfortunately it is all very untimely. He told me starting today he will be on a trip to a 2 week long locksmith conference/training.

Since I have the lock cylinder out I want to give it a shot myself. I have a working understanding of how lock tumbler work.

tumbler partially extracted from cylinder bore

 
I worked on it to extract the tumbler from the cylinder but it cannot be done because of the key stub and the other 10 or so pins. I tried to remove the pins and springs. There is no way for them to come out and I suspect they are designed to be non-serviceable.

I figure out I can verify this if I go to the dealer parts department.
 Mercedes' part manual shows one can either buy a lock cylinder with matching keys, or just the lock cylinder. The former is less then half the cost of just the lock cylinder. Clearly this is another sign that the latter requires Mercedes to build you a lock cylinder based on your VIN.

I gave it last ditch attempt to remove the key stub with the tumbler back into the bore.  I tried using crazy glue to hold the outer pins compressed. I was able to do so with a few pins but after awhile I decided it is a lost cause.

i tried

I am convince the broken key stub is wedged inside very tight. I went to the dealer.

I was correct that the tumbler pins cannot be extracted in the field. The lock cylinder with the matching key is no longer available. I would not want it anyway because I would have a unique key for just the sliding door. The stand alone cylinder costs ~$86 and requires the VIN and mileage to order.

By now I am convinced the odd my locksmith or any locksmith can extract the broken key is very unlikely. I cut my loss and order the lock cylinder and the handle which the dealer said can be here in a few days. Total of both parts is $110. It had been a lot for work but I learnt something new alone the way.

Once I receive the parts I have to press the lock cylinder into the handle. I am very curious the force require to accomplish it.

My neighbor's wife bent her ignition key with remote control for her VW Eurovan. I told him the key cost $250 or more and he was shocked. I know horror story of folks lost their only remote control key far away from home.

I had never break a key inside a lock in my life. Neither have I ever lost a car key while on the road far away from home.