Hello, all:
Is there an easy way to disassemble the gas cap to inspect the locking function? I can turn the key in mine, but, it never locks (spins free?). I notice that there are three tabs on the inside surface of the red portion that the white portion rides on. I've tried to lever the white portion up over these, but, something seems to be holding it all together. Any information would really be appreciated.
Michael L.
1986.5 Prussian Blue Metallic AT/LSD


To get the gas cap apart you need to immerse it in very hot water to make it more flexible then using three hands pry on all three " Tabs" . Once inside you will find a broken bit which of course is not available as a separate part ....

Jim Bailey


Hi Michael,

Don't know if you'd already disassembled the gas cap, but I just did that a couple weeks ago - with the cap on the fuel tank! I used a 1/8 inch flat blade screwdriver with a square shank( it doesn't bend as bad as the round shank) to pry the tabs one at a time. You have to use a little persuasion, though. I was worried about deforming the red part, but it seemed to get back to its original shape.

Once the tabs have cleared the white part, push on the keyhole to separate the red and white part. I wish I knew how to call them:)

Good luck!

R de Guzman


Hi All,

One quick question for the Rennlisters out there. Is there a fairly  simple way of replacing the lock cylinder in a gas cap? My old gas cap stopped locking properly, so I bought a new one w/ key. Can I swap out the new lock for the old one? Anything to avoid carrying another big 928 key around :)

'88 S4 auto w/ LSD

Re-keying the gas cap lock is actually pretty simple. The trick is getting the thing apart without breaking the plastic. The inner (white) part of the gas cap snaps into the red outer shell. You will have to find yourself something thin and flexible and slide it between the outer and inner shell. I use a couple of plastic shims that also are useful for removing a windshield without cracking it.

You might consider heating the cap a little before starting on it and wearing gloves. I think 200 degree F is probably reasonable. Either wrap it in plastic and boil it or put it in an oven. Heating will expand the outer shell and make it more flexible. Now we can have a debate of how much the inner shell will expand.

Once you are free of the tabs holding the two pieces together the inner part just slides out. From there it will be easy to see how to remove the cylinder. You can just take the tumblers out and swap them around. There are four different sizes and I believe the gas cap lock is not fully populated. Just make sure the little - hell tiny - springs remain in the cylinder since they are what makes the lock work.

You can try to just swap the cylinder from the old cap, but the tumbles can get worn and not all cylinders are the same.

On trick to remove a cap that is stuck on and just spinning or locked and you do not have a key is to drill a hole through the top of the red plastic and insert an awl. This locks the two pieces together and allow the inner part to twist off. Just be sure to drill inwards to avoid hitting the tank material.

One other tip. If you have all the new tumblers in and are using a slightly worn key I put in the key and then touch the any edges of the tumblers sticking out with a small fine file. This will prevent any stickiness or catching.

But then I am sure 928 International can do it for you too. If when you are done you have any miscellaneous parts left over I will be glad to take them. Get enough parts and a couple / three broken caps become one good one.

Good Luck

Dan Brindle

I was curious about this because the cap on my '84 doesn't work -- the key works in the tumbler, but the cap doesn't lock.

When the cap is locked, is the handle supposed to free-wheel when you turn it? The owner's manual doesn't say.

Anyways the pics show the disassembly procedure. Take a flat-blade screwdriver and gently pry off the plastic piece. If it seems like you are going to break the plastic, move the screwdriver about 45 degrees around the cap and try again. Don't worry, the plastic won't break.

Then pull out the tumbler assembly out from the cap. There is a U-shaped retainer which you remove, and at that point the tumbler comes out of the housing.

After disassembling mine, I found a broken plastic cam (see last pic). I'm not sure if this really explains my non-working cap. It seems like the owner replaced the little spring with a much more forceful spring, with the result that the cam doesn't retract back into the white plastic tumber housing, but I doubt anyone would go to that much trouble.



I kinda thought that the cap should pry off, and I tried really hard but it would not come off.
It already has a chunk broken out of it, did not want to break anymore.


The Gas cap has no metal lock barrel retainer and will need no drilling. Inside the cap between the red and white sections are three molded plastic retaining flanges, (on the red part) that lock onto the shoulder of the white center section. Warm the red portion with hot water or a heat gun until the flanges are flexible, and, using three hands and 3 flat blades, CAREFULLY force back the tabs while pushing on the key to press the white section out of the red cover.

Jerry Feather made this solution to open the cap locks. He is making and selling a complete device for doing this in a professional way.