Locking Gas Cap

This component is part of the Fuel Tank.

Caution when using the locking gas cap. Fuel is dangerous!


Sedan Gas Cap
  • The proper cap for W113 cars is Unvented.
  • When tightening the cap, be sure to turn the cap clockwise until it has definitely hit the stop position...turn the cap about 1/3 around or more.
  • The inner cork (or rubber) lining is fairly thick on some caps and will cause the cap to tighten and appear to be fully seated before the cap has reached the actual stop point. The key can be turned and removed from the cap at this point and the locked cap will spin and appear to be properly seated but after driving a while, a cap not fully seated can fall off.
  • Best to try to turn the cap hard clockwise a few times to make sure it cannot turn further before locking the cap.

Chromed SL gas cap.

The sedan gas cap on the right is identical in construction to one type of chromed SL gas cap.

Filler Cap Key Numbers

If a car was sold originally with a Ymos cap the lock number for the key is stamped on top of the hexagonal column between the words "Ohne" and "Lüftung". It usually reads something like "TA077" where the "T" indicates either a door key or a fuel filler cap key ("Türen und Tank"). Sometimes this leading "T" was omitted and only "A077" or similar identifications are seen. If the lock number is missing then this is most likely a replacement cap.


It is not possible to replace cylinders in caps made by Huf:

Huf gas cap


The process for taking apart a locking gas cap is as follows:

Re-assembly is the reverse of the foregoing information.


Components on the Back of Fuel Cap

On the back of the Fuel Cap there is a retaining collar, spring, locking collar and cork seal.
The hexagonal column has a groove cut into the corners and also has a locking notch in it.

Removing the Retaining Collar

The locating tab needs to be prised out of the notch.
Push down on the retaining collar and turn at the same time until the collar is free to be removed.
The locking washer and spring will lift off.

Note : If all you want to do is replace the cork gasket then this is where you prise out the old gasket and install the new one.

Replacement gas cap seal (gasket) is available from Mercedes with a choice of cork or rubber. They are for two different locking caps but both the cork seal and the rubber seal fit a locking cap.

The part number for the rubber seal is: 140 471 00 79. ($3 in June 2008.)

Re-assembly is the reverse of the foregoing information.

Removing the Free Spinning Collar

On the circular disk there are 2 small oiling-type holes one of which will be half covered on the inside.
Insert a small screwdriver in there and push to the outside of the collar and pull on the column, the whole column section will come off of the free spinning collar.
Note : The key moves a small metal piece that slides in a groove. It is under tension of a small spring that can jump out.

Removing the Key Tumbler

The key tumbler mechanism is retained in the circular centre spindle by a C- clip.

Note :When removing the tumbler, the Key must be inserted to prevent the small pins inside the tumbler from falling out.

At this stage the key combinations can be changed.

Further Dismantling

The chrome collar on the tumbler is held on by two pressing points. It can be removed by prising them apart.
Only do this if you really NEED to.

Below are instructions on how to replace the cylinder in a Ymos locking gas cap.