Piston Slap: Fuelish thoughts on dropping a gas tank?


Viktor writes:

I own a 1954 Plymouth Belvedere with a screen/filter inside the gas tank. I need to get in there and get the filter cleaned or replaced. Is dropping the tank a job I could perform myself?

Sajeev answers:

If you’re like me, dropping a fuel tank is a miserable experience. But that’s mostly because I’ve had the misfortune of doing the deed with 10+ gallons of gas in it, lacked a lift, and lacked adequate help (at least initially). But I learned a fair bit from the experience, so I recommend any able-bodied person to try it, provided they drain the tank before dropping it.

The tank in question. eBay | Moparpro

From what I see here, the Belvedere is a pretty straightforward chassis in the gas tank department. There are two straps, bolted at one end and slipped into the body at the other. There are hoses that connect the tank to the filler neck and the engine, consider replacing them all if they are 20+ years old. Protect the tank during this procedure by putting something between it and the jack, like a plank of wood. Don’t have a jack? Get a friend to help.

With a floor jack underneath to take the load off, unbolting the straps will be easy (use penetrating oil if corrosion is problem), and the tank will take a controlled fall down to Mother Earth. Once on the ground, it’s only a matter of a few bolts (or possibly a locking ring, removed with a flat tool tapped free with the help of a hammer) to pull out the filter/screen assembly you mentioned.

To be honest, installing a new sending unit might be a good idea at this point too. Do what you see fit to the tank, raise it back up to the chassis (with a friend or a jack), and reinstall the straps. Because of the location of this part and its potential exposure to corrosion, the bolts might be hard to re-install after all these years of use, so use penetrating fluid on the threads (or chase them) to ensure nothing strips out.

That’s it! Honestly, I made it sound more difficult than it truly is; odds are you won’t need to chase threads and spray penetrating oil, but I threw it out there just in case. So drain the gas tank, get the tools handy (i.e. cut a piece of wood for a floor jack beforehand), and recruit a friend to help. Time everything right and it can likely be done in a couple hours or less!

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    Like a lot of things, dropping a fuel tank is generally “more easily said than done”, so don’t get to thinking that Sajeev has over-stated the task. Anything that’s been exposed to decades of wet roads, grime, and potentially salt or other ice-melt chemicals will likely fight you more than a little. If not, consider yourself lucky. Having said that, I think the advice given is sound…just don’t set out to do the job in a “couple hours or less” with a commitment to have the car somewhere in three hours. If it works out that way, great, but more likely you’re going to run into some things that will take up to DAYS to get loose and/or effect replacements of repairs to unforeseen recalcitrant parts.
    As just one example of potential problems which Sajeev glossed over: many cars in the past were given heavy applications of tar-like undercoating (I used to do it to all my vehicles in the ’70s through the ’80s). If your car has it, you might take several hours just to LOCATE the strap bolts and drain plug, let alone loosen them! 🙄
    It’s not an earth-shattering job on a ’50s car, just be ready to face some challenges and not think you’re going to just zip through the job without issue. Other than that – go for it!

    Well, I’ve owned quite a few ’50s era vehicles, and have dropped more than a few tanks in my day, Sajeev, so we’ll just chalk it up to experience! 😉
    I would almost bet on rounding off a fitting or breaking off a bolt due to excessive corrosion, too, but I don’t know the actual undercarriage condition of this Plymouth. However, if original to the car, I’ll definitely lay excellent odds that the tank doesn’t look like the picture you posted (clean, shiny, undented, etc.)!

    If it is a steel tank (which I imagine it is), one thing to be prepared for is that all of the points where the fuel tank makes contact with the body are rotted. The other thing to be prepared for is that the steel lines in the frame are rotted too.

    My recent tank drop for my 94 Blazer ended at around a grand in parts and every part of the fuel system from the tank to the throttle body being replaced. Your example is probably a bit mechanically simpler but be prepared for some surprises.

    If you are doing this without the benefit of a lift, get your hands on some scissor jacks – you know, the ones that come with the compact spare in most cars. If you can round up at least three of them, even a partially loaded tank can be dropped with a minimum amount of grief

    Here is the deal.

    Sanjeev covered it well but there are key points to notice with what he said.

    #1 Drain out as much as you can. Empty tanks are not heavy.

    #2 Have at least one other person. This in most cars is a two person job. Even a third can help if you miss a ground wire.

    #3 How rusty and how rotted can depend much on where you live or where the car was from.

    We did a tank in a car last year that sat for 20 plus years. Once out we inspected and even though the car was in good shape the tank was damaged inside. While out that is the time to check many items and often best to replace them. If a new tank is available now is the time to do it. Same with the sending unit and straps. Replace any rubber hoses on the lines that may be hard to reach. same on clamps.

    Pulling an average tank is not hard just takes a bit of planning and 4 hands.

    Now some cars can be a major issue as in the later Corvettes where the rear suspension and exhaust and transaxle must be removed. Unless you have the tools it can be a task. Note the later Vettes have a panel to replace the pump from inside the car. They fixed the issue.

    On a 1950 Hudson, the inlet and screen can be removed from the tank without removing the tank from the car. Likewise, the gas gauge sender. The front of the tank is angled, and these items are attached to the angled part with small screws. There is just enough room to get them out.

    Before I took out the tank, I would take a careful look at these items.

    Good advice, but if the picture that Sajeev included in the article is accurate, the sending unit is in the center of the top of the tank (that’s the filler inlet and vent tube in the corner) and likely not accessible like the Hudson. However, there is always a possibility of enough room or other access methods that should indeed be investigated before just launching into a full-on tank removal. Older cars often have a lot more room designed into them than newer stuff (I’m totally ignorant of what 1950s MOPARs are like under there). Additionally, there are “mods” that can be made. For instance, a buddy with a ’69 GTX was having fits with an in-tank pump/filter unit for his aftermarket EFI set-up. After a couple of removals, he said, “I’m not dropping that tank anymore!” (And he has the benefit of a hoist). He cut an 8″ x 8″ panel out of the trunk floor and put some tabs on it with Dzus fasteners. A split rubber vacuum hose covers all of the edges of the panel and hole. A rubber mat covers the trunk floor and hides it all. Voila! Easy to turn four Dzus heads, lift the panel, and have 100% access to the top of his sending unit, pump, and filter where they enter his tank.

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