Gas Cap seal fixed/charcoal cannister deletion?

[kat]

I have noticed gas leaking out under my gas cap and a blackish soot around it. Lucky, my Bronco isn't painted yet but hopefully soon.
But for the life of me I can't find the replacement seal for it on any of the vendors sites. I have duel tanks and really don't want to buy new caps for both of them if I can find a seal. My end game is to put black billet covers on my stock caps.
Thanks for any direction

 

[Broncobowsher]

Never seen that seal available separate. Replacment cap is the only fix I have known about. Pretty common replacement due to failing emissions.

 

[kat]

Never seen that seal available separate. Replacment cap is the only fix I have known about. Pretty common replacement due to failing emissions.

That's what I was afraid of...thanks

 

[71broncman]

I have made my own replacement seals out of some thin rubber sheet material. I have a couple on my 75 F250 that have been on there for 6 or 7 years, with no signs of failing. I also have one on the main tank on the Bronco for a couple of years too. I've found that the rubber that is used on the new replacement caps starts failing after a couple of years. The rubber I use an EPDM, which has a better resistance to heat, sunlight, and ozone, than nitrile (which is more resistant to oils and gasoline). This works for me, and I don't have to buy a new gas cap every couple of years.
Mark.

 

[DirtDonk]

But you also have another issue, and that's that to have gas leaking out the cap you have to have gas backing up into the filler neck. Which does happen of course, but it's not supposed to.
If it's a factory tank it should have an air space unless you top off when you fill. If it's an aftermarket tank I'm pretty sure most of them leave it up to the fill-er (you) to not fill it all the way.

A new cap and gasket "might" fix the leak, but then again it might not. Vapors don't push hard so don't always need a perfectly tight seal. Liquid gas can push hard under the right circumstances and may just push past even a brand new seal.
Besides, these were not always the best fitting caps and fillers anyway. Plus if there is any damage/deformation to the seal surface of the filler neck from age and thousands of fillings, you may not get a perfect seal even if the cap could do that.

Are you still running a fully functional charcoal canister system? Yours would in theory have had the then-new style with the canister on the firewall and nothing next to the driver's shoulder.

Good luck either way. Maybe a little bit thicker material than original and make sure that the filler opening is smooth?

Paul

 

[kat]

I have made my own replacement seals out of some thin rubber sheet material. I have a couple on my 75 F250 that have been on there for 6 or 7 years, with no signs of failing. I also have one on the main tank on the Bronco for a couple of years too. I've found that the rubber that is used on the new replacement caps starts failing after a couple of years. The rubber I use an EPDM, which has a better resistance to heat, sunlight, and ozone, than nitrile (which is more resistant to oils and gasoline). This works for me, and I don't have to buy a new gas cap every couple of years.
Mark.

I actually thought of that but had no idea what kind of rubber to use. For future reference what is EPDM and where would I buy it?

But you also have another issue, and that's that to have gas leaking out the cap you have to have gas backing up into the filler neck. Which does happen of course, but it's not supposed to.
If it's a factory tank it should have an air space unless you top off when you fill. If it's an aftermarket tank I'm pretty sure most of them leave it up to the fill-er (you) to not fill it all the way.

A new cap and gasket "might" fix the leak, but then again it might not. Vapors don't push hard so don't always need a perfectly tight seal. Liquid gas can push hard under the right circumstances and may just push past even a brand new seal.
Besides, these were not always the best fitting caps and fillers anyway. Plus if there is any damage/deformation to the seal surface of the filler neck from age and thousands of fillings, you may not get a perfect seal even if the cap could do that.

Are you still running a fully functional charcoal canister system? Yours would in theory have had the then-new style with the canister on the firewall and nothing next to the driver's shoulder.

Good luck either way. Maybe a little bit thicker material than original and make sure that the filler opening is smooth?

Paul

Well I TRY not to over fill. When the pump clicks I stop, I can hear the gas rushing up the tube. I am not running a charcoal canister. The surface on the necks look fine, but since I have already bought the new gas caps I will keep an eye on what happens next. I don't smell gas but can see a stain of it on the body under/down the body like its doing it when I go down the road. The black soot around the caps had me baffled though...thanks Paul

 

[Glass Pony]

Dirtdonk makes some good points.
The gas cap I had it was held together with a big square rivet. It was loosening up and the gasket was shifting so the cap had to be replaced.
If the gas caps are going to be painted body color I would get new ones and better yet get a third one and send them all with the Bronco to paint.
Ask me how I know this.

 

[Broncobowsher]

If you are doing a body colored gas cap and getting a new one to start. I would get a couple spares and let them all get painted. Because if you don't you will loose it, or maybe even worse drop it and scratch up the paint and have that in your hand. If you have a spare (or two) at home, you will probably never need them.

 

[kat]

Dirtdonk makes some good points.
The gas cap I had it was held together with a big square rivet. It was loosening up and the gasket was shifting so the cap had to be replaced.
If the gas caps are going to be painted body color I would get new ones and better yet get a third one and send them all with the Bronco to paint.
Ask me how I know this.

If you are doing a body colored gas cap and getting a new one to start. I would get a couple spares and let them all get painted. Because if you don't you will loose it, or maybe even worse drop it and scratch up the paint and have that in your hand. If you have a spare (or two) at home, you will probably never need them.

I don't plan on painting them, Im putting billet covers on them once I get them. And yes I feel your pain on having extra gas caps. Back in the '80s when I had my first Bronco (and before the web) I lost mine and finding another one was a pain in the ass. From then on when I pump gas I keep the cap in my hand...NEVER put down the gas cap...NEVER

 

[Broncobowsher]

I always set the gas cap on the driver's seat. Pointy end up.
Never lost one that way.

 

[kat]

Ok I seem to be having the same issue after replacing my old gas caps. Both the rear and aux tank are stock with no charcoal canister attached. Getting pressure built up and still getting this black soot around the caps.

Auxiliary tank gas cap

Rear/main tank gas cap

Hard to see against the dark color and sanding

 

[75MIKE]

Old inner tube works well.

 

[reamer]

I've always kept the gas cap kinda loos, if I tighten it down, next time I fill-up I hear a "hiss" of releasing suction (almost vapor lock)

 

[kat]

Old inner tube works well.

The fuel caps are brand new

 

[kat]

I've always kept the gas cap kinda loos, if I tighten it down, next time I fill-up I hear a "hiss" of releasing suction (almost vapor lock)

I was thinking vapor lock but why is there black stuff around the cap? Also I would be scared to keep my cap loose, scared it would fall off going down the road

 

[reamer]

vapor lock is a suction action....

 

[DirtDonk]

Never seen the black soot stuff around a filler before. I'm guessing it's not unique to yours, but I've sure not noted it before.

Because your gas caps on the '76 are not "vented" (they don't normally allow vapors to vent outside) you are probably building up pressure and it's leaking past the gasket. The sooty stuff might just be dirt collecting on the slight moist environment left by evaporating fuel spray. Not enough to actually look wet, but enough to collect fine dust.
You might find the cure as "simple" as reinstalling a working evap system that lets the tank breath outward, but catches the fumes before they get into the air.

Paul

 

[reamer]

What would cause pressure in the thank though? if the fuel pump is pulling ( or pushing ) fuel out of the tank, the void must be made up. It must be something in the return system (if you have one) but then again in a stock set-up there is no "pushing" in the return system except for heads and exhaust system...

 

[kat]

Never seen the black soot stuff around a filler before. I'm guessing it's not unique to yours, but I've sure not noted it before.

Because your gas caps on the '76 are not "vented" (they don't normally allow vapors to vent outside) you are probably building up pressure and it's leaking past the gasket. The sooty stuff might just be dirt collecting on the slight moist environment left by evaporating fuel spray. Not enough to actually look wet, but enough to collect fine dust.
You might find the cure as "simple" as reinstalling a working evap system that lets the tank breath outward, but catches the fumes before they get into the air.

Paul

It does build up pressure, when I open the gas cap it does hiss alot. This may be a dumb question but how do I make a evaporator system?

 

[reamer]

Hiss is the vacuum, Air going in....