1969 GT500 Gas Tank Vent Tube / Fuel Vapor Line

[stangs-R-me 120]

Just noticed a 1969 Shelby "Fuel Vapor Line" on CJP yesterday ...

https://www.cjponyparts.com/69-70-shelby-gt500-om-fuel-vapor-line-1969-1970/p/MUV1011O/

This is similar to what my 1967 FAIRLANE had.   There was a small hose barb on the gas tank adjacent to the filler pipe, a short jumper hose between this barb and the vent tube which went towards the passenger side quarter panel.   It then looped around up inside the quarter then bent down and went and met with another short hose that exited out somewhere in the bottom of the trunk drop-off.

I always wanted to duplicate this on my Mustang and would have added a threaded bung to the inside of the fuel neck so I could screw a hose barb fitting in it ... would have needed to design & bend a tube run to make it look stock, so I just never got around to it.

I'm guessing they had to do this on the Shelby's because the exhaust port was directly below the gas filler and having gas expand and leak out of the vent-dent and onto the exhaust port would not have been smart !!   Not that it is wise to have gas leak all over the LP light either, but it was obviously acceptable on regular Mustangs. 

So the question is, where was the small hose barb ... on the gas tank like my Fairlane or on the filler neck ??

Anyone have pictures they can share as I'm very tempted to adapt this much better vent system to my Mustang.

Doug 

Edited February 12, 2018 by stangs-R-me
edited title to better fit discussion

[stangs-R-me 120]

Went searching on the concoursmustang forum to see if I could dig up any more info or photos on this fuel vapor line.

I did not find any pictures, but it was apparently a recall - fix for 1969 & non California 1970 GT500 only.  

All GT500's just like GT350's left the factory with a non-vented gas cap and vent-dent filler neck like regular Mustangs, and this recall included flattening the vent-dent and this added fuel vapor line along with other hardware for the install.   Filler pipe was then modified to accept a hose fitting.

Doug              

[69ShelbyGT350H 61]

From what I read, it was a recall only for the 69/70 GT500. GT500's were said to have "Pop Back", where unburned gas would ignite in the exhaust system and could potentially ignite any raw fuel that has spilled out of the vented gas cap and onto the exhaust pod. Guess the GT350 did not have this issue with the "Pop Back" ?

[Ridge Runner 1,112]

Torinos had the same vent tube as the fairlane ,it was a nipple in the filler tube ,a short piece of rubber fuel line connected to a metal tube that ran down the tail panel and folded up into the top of the quarter and exited through the bottom of the rear of the lower quarter,i believe there was a flapper valve on the metal line were it exited through the quarter

[Vicfreg 771]

Here is what I found....  Here is the link, text below.    Also lot's of stuff on these vented fuel tanks and design related to the 1971 and later Pinto fires.  This is why the Ford "service" replacement gas caps for the cars with flip down gas caps were the screw on type.  My 1968 Mustang has a flip down gas cap, and it has popped open on occasion....    

 

https://www.diyford.com/shelby-mustang-history-19691970-gt350-gt500-end-line/

 

 

....But the crowning achievement of the Shelby-unique rear fascia styling had to be the exhaust pipes, which exited in the center of the rear face.  But the great appearance was not without issue: the close proximity of the vented fuel cap to the exhaust outlet might not have been one of Shelby’s better ideas from a safety point of view. The fuel cap continuously vented gasoline vapors from the tank, resulting in a fuel vapor cloud lingering around the fuel cap. Fuel vapors, being heavier than air, tend to settle toward the ground, and as the fuel vapor cloud settled, the design of the car’s rear fascia dictated that they settled right into the area of the exhaust outlet.

Under certain running conditions, when the carburetor was set just right and there was a rapid backing off of the throttle, the engine could backfire. It was known as “pop back” and it was unique to the GT500’s 428 powerplants. On a couple of occasions, this pop back ignited the fuel vapor cloud and actually set the tail end of the car on fire! It was incredibly ironic that one advertising tag line for the 1969 Shelby was “fire, and refinement” but that was not the kind of fire either Ford or Shelby Automotive had in mind. The fix was to install nonvented fuel caps and replumb the fuel tanks so that they were vented via a hose that exited at the bottom of the rear quarter panel, away from the exhaust exit.

GT350s and their 351 powerplants were not subject to pop back and didn’t receive the plumbed tank venting. The whole deal was a very close call, as some worst-case engineering analyses actually had the pop-back ignition of the fuel vapors work its way back to the fuel tank, causing an explosion. The few fires that were experienced were small and, save for some damaged fiberglass and paint, caused no catastrophic effects.

 

[stangs-R-me 120]

Thanks for that Vic ... don't think I've ever seen/read such a detailed write up on '69-70 Shelby's,  however no pics of how this recall vent tube was run (not that I really expected any). 

My Scott Drake repro GT Gas Cap assy. came with both the OE plunger set up as well as a screw on cap.   I initially set it up with the now "show-only" plunger since my car survived all these years & 150k miles like this already, but switched to the screw on cap because it really is a much better solution. 

I ended up ordering the vent tube assy. from CJP as I really think this is the best tank vent solution for ALL classic Mustangs, not just the one application that Ford decided to do a recall on.   I'm sure the taller Mustang (vs. long & skinny Shelby) Taillight is going to be in the way, but having the tube will give me an idea of how it needs to be run.   I'm hoping just a few tweaks to the Shelby line will make it work, but if not I'll just bend a new line and once past the taillight, duplicate the bends of the Shelby line so it terminates at the same point.       

It has been probably 30 years since I had gas expand and come out between the cap & filler neck and run down my paint job.   But I learned how to avoid it ... key is to never fill up with gas without putting some miles on before parking it in the sun on a hot day.   That I've not put more than 500 miles on it a year for 25-30 years either, so less chances for it to happen. 

Doug  

[Vicfreg 771]

Doug, where and how does it connect to the filler neck?   I am interested in this also

[stangs-R-me 120]

20 minutes ago, Vicfreg said:

Doug, where and how does it connect to the filler neck?   I am interested in this also

Posted on the concours forum figuring if anyone had what I was looking for someone there would.   Soon after Jeff Speegle posted some pics as well as the RECALL instruction sheet ...

 http://www.concoursmustang.com/forum/index.php?topic=17420.new#new

... like magic, all the info I was wanting !!

Looks like the tube will pass by a regular Mustang taillight bucket without too much problem as well.

Doug

[stangs-R-me 120]

Studying the install drawing (with a magnifying glass as it is a bit small & blurry), here is what I see:

Drill & Tap 1/8" NPT (actually says pierce a 5/16" hole) 7/8" from back of fill neck flange at a 45Deg angle towards passenger side.

Flatten out the VENT DENT on the filler neck.

Drill a 9/16" hole in the SIDE of the truck drop off 7" forward of B-U light hole & 4" down from floor.

Drill a 1/2" HOLE in the frame rail 1" from the bottom and guessing 6" (hard to read) from closest hole to the rear.   I'd make it so it is inline with the one in the drop off ... if this is 6", then good to go.

Run a piece of fuel line hose from the tube in the trunk out the drop-off (seal with body sealer), and then into the frame rail.   So any fuel that makes it this far will drip inside the frame rail and eventually evaporate.  

Heck I'm 99% sure my Fairlane's hose just hung out the bottom of the quarter panel near the trunk drop off, so they are getting a bit more sophisticated with this install.

Doug

 

 

[Vicfreg 771]

Wow. That is really wild. I have never seen that modification. Also not sure I would dump fuel in the frame rail.   But, very cool to see the original instructions.   

[stangs-R-me 120]

Vent tube is still on back order at CJP, but ordered up another filler neck this morning because I had $10 in RPM points expiring today.  

The new CJP filler neck I just installed 2 weeks ago with the "unleaded nozzle insert" in it ...

... did not come with a "vent-dent" like it should have so I added one.   With this GT500 Vent Tube a neck with "no vent dent" is required, so figured I'd order up another neck before my RPM points were gone.

I've also come up with a solution for installing the 1/8" NPT hose nipple in the filler neck.   I plan on using a McMaster Carr 6630K14 1/8" NPT Lock Nut on the inside and either a 2nd lock nut or a washer & gasket on the outside sandwiched between the fitting's hex and OD of filler neck:

Not sure if I will run the hose into the frame rail or let it just drip on the ground like my Fairlane did.   Will figure all this out and do the actual install in the Spring when car is not tight against the back of my garage hibernating.

Doug

[Shep69 149]

Doug our early Aussie falcons had a similar set up . The filler was vented with the fitting pictured below and then run into the wheelhouse. I was thinking about doing this as well .

 

[stangs-R-me 120]

Mark ... thanks for that, interesting that for what I'm assuming to be a factory installation they still modded the neck. 

$17.50 is kinda steep though, the McMaster nuts are $2.22 US Each + s&h.   I can order extra nuts if you (or anyone else) wants them added to a filler neck INSERT order.

Doug

[Shep69 149]

8 hours ago, stangs-R-me said:

Mark ... thanks for that, interesting that for what I'm assuming to be a factory installation they still modded the neck. 

$17.50 is kinda steep though, the McMaster nuts are $2.22 US Each + s&h.   I can order extra nuts if you (or anyone else) wants them added to a filler neck INSERT order.

Doug

Those ones I posted are designed to be welded in Doug. I assume you were going to try and put it in without welding . 

I would be interested to see how this could be done . The fitting in the photo has a large shoulder so you could possibly cut a thread on the outside and fit a nut to secure it. 

They were originally factory fitted .

[stangs-R-me 120]

14 hours ago, Shep69 said:

Those ones I posted are designed to be welded in Doug. I assume you were going to try and put it in without welding . 

I would be interested to see how this could be done . The fitting in the photo has a large shoulder so you could possibly cut a thread on the outside and fit a nut to secure it. 

They were originally factory fitted .

Fitting in picture looked to be BRASS, so I assumed it went on the inside and had some sort of gasket sealing.

That makes much more sense, but the goal here is to be able to remove fitting so you can get the neck in & out AND to avoid needing to have the whole thing re-plated ... so yes, no welding.

Doug        

[Vicfreg 771]

I am thinking of using a fuel cell bulkhead fitting.  6AN needs a 9/16' clearance hole, so should work.

https://www.summitracing.com/parts/vpe-16892?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-vibrant-performance&gclid=EAIaIQobChMIubCu2v-d2QIVSi-BCh1Y_QFyEAQYBSABEgJcg_D_BwE

[stangs-R-me 120]

2 hours ago, Vicfreg said:

I am thinking of using a fuel cell bulkhead fitting.  6AN needs a 9/16' clearance hole, so should work.

https://www.summitracing.com/parts/vpe-16892?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-vibrant-performance&gclid=EAIaIQobChMIubCu2v-d2QIVSi-BCh1Y_QFyEAQYBSABEgJcg_D_BwE

Too bad they don't offer a -4 size (7/16") which is closer to 1/8"NPT.   Larger the dia. the harder it is going to be to flatten the radius of the tubing enough to seal.

Doug

[stangs-R-me 120]

I finally got the vent tube from CJP last week and have it mocked up in my trunk.   They thankfully shipped it in this huge 12x16x37" box filled with air pillows so they did not tweak the tube to get it to fit in the box like they typically do for tubing.   Tube actually makes a bend towards the drop off (vs. pointing straight down as shown in the recall diagram), so I will just put the hole where the tube is pointing at.   

Dimensions on the blurry drawing (thanks Jeff Speegle) ...

http://www.concoursmustang.com/forum/index.php?topic=17420.new;topicseen#new

... appear to be 4" from B-U lamp hole and 4" down from the drop off which closely matches where the tube is pointing to.   If these two dimensions really are 4 & 4", the drawing is definitely NOT drawn to any scale as the horizontal 4" is 2.5 times longer than the vertical 4".   Then the frame rail dimension appears to be 6" back and 1" up which would not line up with the other hole like the drawing shows.

There is a rib in the drop-off that is about 4" back from the back-up light wiring hole, to the center of this rib is about 4-5/8".   With tube installed in trunk with tube clamp at the outer taillight mounting screw (per drawing & pics), the jumper hose between tube & nipple at the neck, and some pitch on both the run from the neck & after the 90Deg bend in the quarter, the hole needs to be around 2" down in the center of the rib.   If the hole in the frame rail is really 6" forward of the front tie-down bracket bolt, that would be about 9" forward of where the hose comes out of the drop off.   In the last pic showing the drop-off & frame rail, the black marking in the upper left corner is where the hose would come out and the circled mark in the lower right in the side of the frame rail is 6" forward of tie-down bolt & 1" up.

Doug
 

[stangs-R-me 120]

Modifying the neck for the nipple ...

Drill 13/32" hole using a step drill 7/8" back from the flange at a 45Deg angle per drawing (used a tape and centered halfway between 12:00 and 3:00 spots):

Need an 1/8"NPT x 5/16" hose stem and a 1/8"NPT sealing nut (5530K14 from McMaster Carr).

Put gas cap on and capped off nipple then filled with water to test for leakage. 

[Shep69 149]

Hi Doug. What are you sealing the vent fitting with. 

[Machspeed 219]

If I may ask, am I missing something here? I fully disassembled my 69 Mach 1 and don't recall any kind of vent apparatus. Never recall any issues either. Why this? 

[stangs-R-me 120]

9 hours ago, Shep69 said:

Hi Doug. What are you sealing the vent fitting with. 

The pipe nut has a Teflon ring that seals against the threads as well as the surface.   I will be adding either a small gasket or permatex between the outside washer & the neck upon final installation as well. Just nice to see the Teflon in the nut actually did make it leak free by itself.

[stangs-R-me 120]

2 hours ago, Machspeed said:

If I may ask, am I missing something here? I fully disassembled my 69 Mach 1 and don't recall any kind of vent apparatus. Never recall any issues either. Why this? 

As I mentioned in the first post, I had a '67 Fairlane Hardtop and it's gas tank was vented in a similar manner.   To me, it just seemed to be a way better way of venting the tank and I always wanted to design something similar for my Mustang.   The Mustang gas tank is vented by a dent in top of the face of the filler neck ... this was likely cheaper than using a vented cap and definitely cheaper than having a vent tube.       

Back in the 80's when I used to drive this car all Summer, there were many times where I had the car parked out in the sun and the gas in the tank would expand and run out of the filler neck and down on the paint as well as all over the licence plate light.   A sure way to have this happen was to fill up with gas and then park it.   After having this happen a few times, I then would only fill the car up with gas when I knew I would be driving some miles afterwards or was going straight home and putting it in the garage.    Even following this routine, I had it happen a couple of times so I obviously did not burn enough gas to get the level low enough to avoid the issue.    

 The Fairlane filler neck was behind the license plate in the bumper and unlike the Mustang, there is no painted body surface or LP light below the fill neck.   I had gas expand in this Fairlane a few times and since the gas cap was old and did not seal very well, gas would drip on the ground behind the licence plate rather than go up the vent tube.   No paint to get damaged and the LP light is above the neck, so no real big deal.   Finally found a NOS non-vented gas cap for the Fairlane and that fixed it.

Ford did make an attempt to keep gas off of the Mustang LP Light Assy. by installing a $0.50 rubber flap over the light, but was this a real and effective solution ??

To me, a Mustang with its painted taillight & lower valiance panels as well as a light assembly located below the filler neck needs this feature more than the Fairlane did.   And since Ford Engineers went through the effort to actually design a retro-fit vent tube kit for the '69 Shelby GT500 recall, you bet I want to install a similar set up on my lowly 351W GT Hardtop.

Regular Mustangs obviously don't have the Shelby central exhaust exit directly below the gas cap that caused the issue and prompted the recall (interestingly only for GT500 even though GT350  shares the same set up).   But are the issues stated above not good enough reasons ... if not safety reasons ... that make this a worthwhile mod for any '65-70 Mustang ?? 

The only classic Mustang application that would not benefit or need this mod is a closed loop EFI conversion with a vent canister.

Doug

            

[Machspeed 219]

Very informative, thank you, Doug! I never noted any issue with my car in this regard, thus the query.   Thanks again!

[stangs-R-me 120]

Not liking how the GT500 vent ends up in the frame rail, I've been racking my brains on how to improve this part of the recall installation.  

I've scanned in both the '67 and '69 Fairlane fuel system diagrams and attached below.   The one on the '67 exits the trunk floor drop-off towards the back on the passenger side just as I remember.   On the '69 Fairlane diagram, it looks like it exits the trunk floor BEHIND the gas tank towards the center of the car.   I'm thinking the reasoning behind this is the '67 Fairlane with dual exhaust had the tail pipes exiting behind the rear tires and in '69 on certain models they can also exit straight back like a Mustang.   '67 vent tube location would have likely been too close to the passenger side tail pipe so in '69 they routed the tube inward and behind the gas tank.  

Really like the idea of getting this out from behind the left rear tire AND further away from the left tailpipe.   So instead of just drilling a 9/16" hole through the drop off so the hose can pass through it per the GT500 recall, I'm going to put a 1/4" Female Pipe bulkhead there (207-04-04-STL, pdf below).   A 1/4" pipe to 5/16" hose barb will then go on the trunk side with a short piece of hose connecting it to the vent tube.   On the outside, I'm going to put a 90Deg male pipe to inverted flare fitting and run a second 5/16" tube run towards the back, 90 bend then over the exhaust tip behind the rear valance.   It will then bend down 90Deg behind the gas tank with the tube ending near the bottom of the valence.   I will install a tube clamp to support the end of this tube run close to the 90Deg bend and it will have some pitch to it as it goes towards the center so any fuel that ever gets this far can run out.   Finally, a short piece of 5/16" hose will then be clamped to the end of the tube and drop down about 1" below the valance panel, which is still about 3/4-1" higher off the ground than the bottom of the tank itself so should be in a safe spot.   I thought about just making the tube longer and letting it hang down, but a piece of hose is flexible (if were to somehow get bumped) and is more like how Ford did it on the Fairlane and likely for the same reason.

Much better spot than in the frame rail, behind the left tire, or near the tailpipe !!

Doug

1967 Fairlane Fuel Tank & Vent Line.pdf

1969 Fairlane Sedan Fuel System.pdf

207 Series Bulkhead.pdf