why do 124 lock cylinders fail?
 

on my '87 124 wagon, the driver's door lock recently failed. so this door will not open with the key. have 2 original keys, both look OK, neither work.

so the key stopped opening the door without any warning. it didn't get sticky or difficult to use over time, just stopped a few days ago. this is a bummer because there is a keyless entry / alarm system installed also, that has worked perfectly for about 7 years, and about 2 months ago that failed, burned component on the board, so we had to go back to using the key to open and lock the doors. now the only way to get in the car is the passenger door, the hatch lock doesn't work either. it's a mess :-( this is otherwise a car a car that's in really good condition and well maintained.

the ignition lock did the same thing a few years ago, however the ignition cylinder, in retrospect, probably gave some warning before it fail however i didn't recognize the signs 'til it was too late. now i have to get the bad cylinder out and replace it, have searched on doing it and it looks like by taking the door apart and loosening the latch i should be able to remove the cylinder without the key being able to turn it.

i am wondering what people's theories are as to what makes the lock cylinders fail.

Wear and tear? I dunno, it's 25 years old. Most other vehicles would have already gone to the junkyard due to engine failure.

When I removed the ignition lock cylinder from my 1991 300CE, it came out in 2 pieces. The brass parts were pretty robust and didn't appear to have any problems. IIRC it was the hollow aluminum cylinder housing with various slots milled into it that was the weak point. Some of the milled slots were such that there were only very thin spots that held it in one piece. The collar of the cylinder broke away from the cylinder body.

not sure if this is for real but my wife was just quoted $965.00 for a replacement door lock cylinder. that's retarded. prices on this kind of part are way higher in canada than in the USA, haven't understood why, but this seems ridiculous.

does the cylinder come attached to a new car?

I had to replace mine, I do not remember exactly, but I think it was $350ish just for the part.

i might pay $350 for the driver's cylinder. still looking into how my wife could have been quoted $965 for this part...

Easy answer here...replace the $50 keyless entry unit and move on with more important things.

Good luck!

this part:

GUIDE. CLOSING SYSTEM (Required: 001 LESS KEY,LEFT; BURGLARY ALARM SYSTEM) for Mercedes (1247600777)

is $964.00 from mercedes-benz canada. shocking.

for sure about the keyless entry. it's not a 50 buck system in the car, it's a proper alarm that's been installed into the wiring of the car, not just on the lock pump. i've installed the cheapo lock pump units and they're fine. i tried to repair the board of the unit in the car that failed and that was a waste of time, removing / desoldering the failed chip destroyed the board. i didn't want to cut into the harness yet again with a new keyless system but it's looking like the best solution.

Your lock seized up because of lack of use.

i guess. it's been used a lot in the past 2 months since the keyless unit cacked, but for sure years of disuse prior to that likely has something to do with the failure now.

i wonder if anyone has any rehabilitation tricks, maybe the cylinder can work again?

Try to get it moving with a good rust releaser and remove it from the door clean it up and lube and it will last for years, Many locksmiths can open them and fix them.