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How to Repair Your Ignition Lock


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All parts used in these pictorials are available at the diesel parts for sale page


How to repair your Ignition lock if your key is stuck or broken

So you have got a key that is stuck, or won't turn your ignition lock?  This can be one of the most frustrating things to deal with on your old Mercedes car.  I recently had an 85 300 D in the shop for some other maintenance.  Now I knew the key had been a little tough to turn from time to time, but I ignorantly ignored it.  Well like all things in life, "Mr. Murphy's law" was working overtime that day.  I had just turned off the car and taken the key out of the ignition, when I just knew something was not right.  On instinct, I put the key back in to tried and start the car, but it was not to happen.  Over the next few days totaling several hours, I wore a blister on my finger, used graphite, silicone spray, banged the lock, vibrated the lock with a sander, etc.  You name it I tried it!  Every trick I could find on the internet to get that darn lock to turn, I tried it.  At that point my only real option was to call a lock smith and pay him about $400 to have him remove the hardened steel theft resistant tumbler.  Or was it........

Safety and security tips:

Please remember to recycle all your used fluids at an appropriate recycling center.  Be mindful to not spill or splash fluids on yourself, others or the ground.  Also as a safety tip please remember anytime you are working on, around or under your car, to wear safety glasses and secure the car with wheel stops and approved jack stands! 


Well I don't know if it was the thought of spending $400 on some lock jockey drilling up the car, or me not wanting to be "beaten" by a 20 year old car, but I decided I was going to remove the lock or else.  So follow along on my quest to save the $400 and do it myself......

On this pictorial, I am assuming several things: 1) You are fairly handy with tools 2) You already know how to remove the dash cluster 3) you are not scared to get intimate with the car 4) You are not afraid to do a little "grinding"

I would say this job rates a solid 4-5 on the difficulty scale.  Most DIY'ers can do this, just be patient.

Ok first go ahead and remove the dash instrument panel cluster and set it aside. 

Next we want to "drop" the steering column down a bit.  There are 2 large studs that hold the column to the dash support.  Remove the large nuts and washers.  Don't pull the column down yet.



Now if you could just pull the entire lock assembly off the column, then it would not be "theft" proof now would it?  Looking under the dash at the lock assembly, you will see a U clamp with a large bolt running though it securing the lock assembly to the column.  Remove the clamp.  Now locate the pin that holds the lock to the column.  Normally this pin can be pushed in when the key is turned, but you cant turn your key, so the pin is in the locked position.  What you must do is grind the pin below the surface of the steering column.  ***Now understand by doing this, you may render the steering lock portion of the assembly null and void.  In other words, if you  choose to re-use the lock assembly, and just install a new tumbler and key, the steering wheel may not lock when the key is removed.  If this is NOT acceptable, then you will need to go get a new or used, lock assembly that has the pin intact.

So using your small grinder or dremel tool, grind the pin just below the surface of the steering column.  This was the smallest grinding bit I had, so it made a bigger grind area than I wanted, but it worked.  Next time I would have used a dremel with a smaller bit, and left the column material untouched.  Never the less, my steering wheel locks like it was new after the repair was done because I got another used lock assembly..

When the pin is ground down, you will be able to feel the lock assembly get real loose in the column.  At this point it is time to drop the column down a few inches.  I removed the bolt securing the dash on the left side, right below the parking brake release.  Just look under the dash and you will see it.  This will give you just enough "slop" to pull the column down.  Now very carefully, pull on the dash right under where the ignition switch is, and simultaneously start pulling the steering column down.  As the column starts to move down you will have to manipulate the key assembly to clear the opening in the dash.  You will get the hang of it as you are doing it.  It is really not that complicated, but kind of hard to explain it in words.



When the column is down enough to allow the lock assembly freedom from the dash, then you can just pull the lock assembly out of the column.  Then remove the single wire to the key buzzer.  Also mark the placement of the 2 vacuum lines on their respective ports.  Do not get them mixed up, you car wont shut off!  Don't try to remove the mess of wires connected to the back of the lock assembly just yet.  The 2nd pic is what the column looked like after the lock assembly was removed.



Lock assembly removed and showing the pin ground down on the lock assembly.  The main function the pin has, is to keep the lock assembly from being pulled out of the steering column by a thief.



Now the problem with my lock was sticking tumbler pins, that would not allow the steering column lock to disengage.  By turning the lock up side down and shaking it, then pressing the column lock pawl with my thumb, the key turned very easily.  Viola!  Now I have a turning lock cylinder.  I did this several times and the key would only turn with the lock assembly upside down.  Hmmmm  we may have 2 problems with this unit as we will find out later.  If you key is broken inside the cylinder then shaking it upside down will more than likely allow it to drop out.  You may have to use a small pick and a shaking motion to get it to free up.



Now after you have had your victory dance, and turned the key enough to satisfy your sense of domination, then its back to work.  Turn the key to the second notch on the black ring and leave it there for the rest of this project.  Now you may disconnect the harness assembly at the back of the lock assembly.



Now its time to take out the lock cylinder.  Turn the cylinder with the key to the 2nd mark on the black ring.  Then take a small paperclip and insert it gently between the lock cylinder indentation and the black ring.  Your goal is the get the paperclip into the small hole inside the tumbler.  By doing this, it will hold down the locking mechanism so the black ring will unscrew.  Keep the key and paperclip in their same positions while unscrewing the black cylinder.  


With the cylinder unscrewed, you can pull the tumbler straight out of the lock assembly




This is what the assembly looks like with the lock cylinder removed. Next pic is with the cylinder in the assembly, minus the black ring.   My lock assembly was also defective, so I went the junk yard and got another one that was smooth.  Now we are ready for installation................




Front, side and rear view of the lock cylinder.  Not the small hole that the paperclip fit into on the front.  Note the large square locking pawl on the side that engages the black ring, to prevent the black  ring from turning with the paperclip removed.


This is a close-up of where the paperclip is going, and the hole it goes in.  Note the behind the hole is the lock cylinder pawl.  Normally with NO paperclip in the hole, the pawl is in the up position like it is now.  This keeps the black lock ring from being unscrewed.  Seeing the lock cylinder can help you when removing the lock, because you can see why you need the paperclip.



Take the new ignition tumbler and insert it into the black ring.  Make sure the cylinder locking pawl that will be depressed by the paperclip, is in its proper position in the black ring.  Look into the back and you will see what I mean.  Then turn the lock cylinder to the 2nd position and insert the paperclip to depress the locking pawl.  Making sure the lock cylinder is in the proper orientation to the locking pawl groove.



Reinstall the assembly you just set up, on to the lock assembly.  It may take a few tries to get everything lined up.  Once the cylinder and black ring start to line up, tighten the black ring back down on the lock assembly.  Keep the key and paperclip still, while screwing the black ring on.  Once you get the ring nice and tight, try to make the 2nd hash mark on the black ring, line up with the indentation in the lock cylinder.  It will probably NOT line up perfect, but as long as its close, its ok.



Next is just the reverse of disassembly.  Install the rear harness on the lock assembly.  Slide the lock assembly back on the steering column, making sure the locking pin lines up in the hole you ground down on the old assembly.  If you are reusing the original lock assembly just get it close, but now the steering wheel may or may not lock.  Hook up the "key in buzzer" wire.  Put the clamp back on the steering column but don't tighten yet.  Move steering column back to it upright position and secure.  Install the 2 vacuum lines back on the lock assembly.  Reinstall the lower panel.  Reinstall the dash cluster.

Now test the key and make sure the car will start and shut off.  If it does not shut off you probably got the 2 vacuum lines reversed on the lock assembly.  Put graphite in the lock to keep it working smoothly.

Now that was not so bad was it?