How To: Replace w124 ignition cylinder barrel

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Mercedes Calls it “Lock Cylinder”
Part Number 126 460 02 04 which is £65 + VAT (£76.38)
The shroud Mercedes calls it “Cover”
Part Number 124 462 28 23 which is £10.40 + VAT (£12.22)

Mercedes Croydon quoted £50 to replace it, but only if the key turns the ignition on.

My description below only applies for when you are able to turn the key on.
If you can’t turn the key, keep trying until you succeed (in anything between minutes and days).
I triumphed in turning the jammed key after 45 minutes of jiggling. The success was possibly after I inadvertently succeeded in breaking the inside tongue.
Once your key starts hesitating or jamming, it would be a good idea to replace the cylinder.
Mercedes dealer will be able to order (1-2 weeks) a cylinder that your old keys still fit. Otherwise, you will have to carry 2 keys (one for ignition and another for doors/boot)
The dealer will want to see your V5 and proof of identity to order for you. Non-refundable payment in advance.
The dealer will not give you the ordered key cylinder unless he sees your car. If it is not driveable, you either have to tow it to the dealership or show him a DVLA SORN declaration. Vowing, pleading and begging are futile.

 

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1- Prepare your DIY pin by cutting a thick paper clip at an angle of 45 to 60 degrees. You need 2 of these
Bend the other end so that you know were the bevel is pointing even when it is out of sight.

 

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2- Flatten and smooth the cut edges by filing it or rubbing against concrete.

 

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3- Now your pin is ready. You need 2 of these

 

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4- Remove the lights switch by pulling it forcibly.

 

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5- Unscrew the big #24 nut

 

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6- Have a look at this picture before removing the facia strip. Familiarise yourself with shapes of the hook on the left and retaining clip on the right, to avoid breaking them.

 

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7- To avoid breaking hook or clip while removing the strip, insert a screw driver between clip & hook to free the right clip.

 

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9- Remove the facia strip that covers the key noting the 2 hooks on the left and a single retaining plastic clip on the right.

 

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9- Remove the five 8mm retaining bolts. There will be 3 on the right and 2 on the left.

10- The facia will consequently drop on your lap like in the picture (the 5 arrows point to screw holes).

 

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11 This is all the exposure you need to replace the ignition barrel. There is no need to remove anything else.

 

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12- First of all, let us understand how things work. The black ridge has to be depressed to free the cylinder barrel.

 

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13- We have just inserted the key here. We have not turned the key. The key is therefore still in OFF position. This illustrates why you can NOT access the slot unless your key turns.

 

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14- To access the cylinder latch (the first ridge in the diagram), you have to align the slots together by turning the key. In here, the slots are still NOT aligned and needs a bit more turning.

 

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15- Here, the slots have been fully aligned. The key is roughly half way between OFF and ON.
Some people call it position 1, others Position 2.
I don't care, I just eyeball it. You can't miss it.

 

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16- A front view with the slots aligned. note the ridge (latch) that you will have to depress to be able to free the barrel cylinder. It is the small horizontal line in the top.
You will be able to introduce the pin bevel the wrong way and I think this may either break it or just lock it in place even harder.

 

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17- Another view from the inside. Note the black ridge in the slot above that you will need to depress. Also note the 2nd slot at the bottom.

 

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18- MECHANISM OF THE DEEP LATCH:
This is what you will see after removing ignition barrel and its covering shroud.
When your 2 DIY pins go all the way, they will lift the arms at the 2 long arrows,
thereby pulling the outside RIDGES at the 3 arrows (which act as a latch) to free the shroud.

 

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19- A view of how the key sits in the metal shroud.
Note the inside channel where the shroud will be held in place by the RIDGES (deep latch) of previous picture.

 

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20- This shows you what happens when your 2 DIY pins go all the way in pulling the ridge inside and freeing the cover (shroud).
Here, the latch has disappeared inside.
Compare this picture with the next where the latch is in view.