Is the mach 1 inner (twist) gas cap from under the pop open cover Mustang specific?

[Animal Lawyer]

Was given nice pop open gas door, no inner cap. Is it a mach 1 specific item (in which case does anyone sell them separately? or, is it generic and easily obtainable?

 

[ArtBBQ]

My 71 doesn't have an inner cap. There's a rubber seal on the inside and when you push the cap close that's what seals off the gas tank. 

 

[Stanglover]

 Pop open gas caps were not the safest and why they were discontinued about mid 72's. The repops have an inner twist cap, so the outer is basically a show piece.

The original 71 through about mid 72 only had a rubber disc to seal.

 

[Mister 4x4]

Mine was missing the outer 'flap & seal' portion when I first got it, so I picked up a reproduction flip-open unit with the inner twist cap.  The inner cap only has thumb ridges around the circumference, and is not easy to get completely sealed, or back off again once on. 

I did find a Stant replacement cap at O'Reilly's with some tabs, but they won't let the flap close - stops about a 1/4" short.  With some minor trimming of the tabs, I'm pretty sure I can make that work, but it's just a matter of trial & error and finding time between other projects.  Having the tabs will help greatly, but aside from threatening to wear the fingerprints off your fingers, the inner twist caps with the repops work just fine.

 

[giantpune]

My 73 had a pop open cap on it when i got it.  No inner twisty part.  It just pops open and there's a hole to the filler.  The cap has a rubber gasket that seals on the filler neck's metal rim. I guess its not original to the car but added by a previous owner.

 

[detritusmaximus]

I thought I read that Ford made the change to having a twist of cap and the repros are of that item?

 

[jscott]

My car (Sept. '71 build date)  came with the stock, original pop open gas cap with just the rubber seal.  I recently changed to the repro pop open cap with the inner screw on cap, works and looks fine.

https://www.kentuckymustang.com/Gas-Cap-Pop-Open-1971-1973-ACP-p/1975.htm

 

[secluff]

   Any flip-down style fuel cap with an inner twist-on cap is aftermarket as Ford never released any such setup.
 There were some early '72 Mach 1's that did make it out the door with the flip-down cap. (Just like the 4bl Ram Air cars) Since this was a running change, there is no way to give an exact day the switch was made to the 72/ twist on cap. When '72 production started the flip-down filler cap was still part of the Mach 1 package. Although the Ford part number never changed, the '71 era cap was marked Autolite and had a "D1ZA". prefix. Since Ford was in the process of transitioning from Autolite to Motorcraft in '72, the OE installed flip-down caps could have either brand name and have a "D2ZA" engineering prefix. Ford was still locking horns with the Government over the '71 cap issue. During some accidents and rollovers, the cap was not sealing as well as the twist on caps and was experiencing fuel spillage issues. The '71 caps were revised four times and still did not resolve the leaking problem. All the revised 72 sales brochures and order guides I have (as of 1/72) show the twist style cap on the Mach 1. Since several new emissions and safety-related laws were going into effect on January '72 I can only guess that is when Ford changed the cap and got the Feds off their back. Little did they all know, the Pinto issue was yet to come!

 

[Stanglover]

   Any flip-down style fuel cap with an inner twist-on cap is aftermarket as Ford never released any such setup.
 There were some early '72 Mach 1's that did make it out the door with the flip-down cap. (Just like the 4bl Ram Air cars) Since this was a running change, there is no way to give an exact day the switch was made to the 72/ twist on cap. When '72 production started the flip-down filler cap was still part of the Mach 1 package. Although the Ford part number never changed, the '71 era cap was marked Autolite and had a "D1ZA". prefix. Since Ford was in the process of transitioning from Autolite to Motorcraft in '72, the OE installed flip-down caps could have either brand name and have a "D2ZA" engineering prefix. Ford was still locking horns with the Government over the '71 cap issue. During some accidents and rollovers, the cap was not sealing as well as the twist on caps and was experiencing fuel spillage issues. The '71 caps were revised four times and still did not resolve the leaking problem. All the revised 72 sales brochures and order guides I have (as of 1/72) show the twist style cap on the Mach 1. Since several new emissions and safety-related laws were going into effect on January '72 I can only guess that is when Ford changed the cap and got the Feds off their back. Little did they all know, the Pinto issue was yet to come!

 Steve, I was waiting for you to chime in a clear up the mystery..... or add to it! However, below are my 2 April 1972 Mach 1's. The light pewter one was bought from the original owner in 1980 (as a parts car). Don't be put off by the 73 stripes on it. It needed to be painted and a friend who owned a 73 gave me the stripes. The red one I also bought in 1980. That is the one that got away, I should not have sold it in 1991.

 

[cwalker509]

The first two pics are from my 72 GT-351. It has the separate twist cap. No idea if it is original but the pop open caps WERE std for 72 GT-351. It is spring loaded. The last pic is from my 71 Mach. It flips down and is not springloaded. It has the rubber seal.

 

[secluff]

The Mexican GT351 Mustangs were not American-built and therefore did not have a typical U.S.-type VIN or have to meet the emissions, safety, or any other standards that U.S.-built vehicles had to meet. These bodies were shipped to Mexico as incomplete or Knock Down kits with no VIN. Most people didn't even know these cars existed until a few years ago so accurate info was more than difficult to obtain. What pictures I have seen do show a Mach1 style cap. Since the version with the inside twist cap is an aftermarket item that was not available in the '70s, it wouldn't be original to your GT351. You can see the definite appearance differences between it and the cap on your Mach1. 

The VIN on yours should start with AF01 with the next two letters defining the year and month of manufacture and the next five numbers the consecutive serial number. And by the way...you have some nice vehicles in your fleet. 

 

[Animal Lawyer]

so, does anyone know does acp sell the inner twist cap separately, or alternatively, can I buy a replacement rubber gasket and is there a way to mount it to the acp repop mach1 cap?

 

[MikeGriese]

Are you asking if you can "convert" an aftermarket flip top cap to one that seals to the filler neck without the inner cap?  If not, it's easy enough to make a new rubber gasket if that is all you need on the inner twist cap. 

 

[Stanglover]

Is it me or is the pop open cap on the blue/green car upside down. It would be very hard to put gas in with the cap lifting upward.