1978 Gas Tank Removal/Replacement out of an M body

John Davis

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Has anyone ever removed and replaced the gas tank out of an M body before? Any tips or tricks you can share? Any suggestions on replacement tanks? Are they re-popping these or will this be a junkyard find that's boiled out and restored?

Thanks!

JD
 

Aspen500

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It's fairly straight forward. Unhook the fuel and vent hoses and unplug the wiring. Ideally the tank would have as little fuel in it as possible of course (fuel is about 8 lbs/gallon). Support the tank and remove the straps. Then it can be lowered while moving it to the passenger side to slide the fill tube out of the grommet. It's a good idea to replace the fill tube grommet, and they are available also. If the original sender lock ring is in good shape, reuse it. The aftermarket rings don't fit tight enough in most cases, and then there will be a leak.

The tanks are readily available new. Same tank fits any late '79 and newer F/M/J body coupe or sedan (not sure about wagon to be honest). Early '79 F is slightly for the venting, and '76/early '77 is completely different but that won't affect an M-body anyways so,,,,,,,never mind, lol. The fuel sender is available also for most applications, along with the tank straps.

Here's a link for Rock Auto as an example. You can get them from many sources though.

1984 DODGE DIPLOMAT 5.2L 318cid V8 Fuel Tank | RockAuto
 
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BudW

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It is many times easier if the tank is empty (as opposed to having 18 gallons of gas in da tank), or as empty as you can get.
Having car on a lift and using a transmission lift/lack underneath makes the job many times easier - but for most of us that is a dream

There should be a grounding clip on the main fuel line, that needs to be popped off (and not lost somewhere).
I highly recommend cutting the three hoses (main, return and vapor) and then worrying about disconnecting - after tank is out of the way. Once tank is removed, remove the three hose pieces from lines and from tank to make correct length new sections of hose.

There are two attaching bolts towards the front of the tank. Be sure to soak those bolts a few times with penetrating fluid before starting.
Have a jack to support the weight of the tank before removing the bolts. With tank supported and bolts out, allow the straps to drop down. You can then twist the straps so they can come out of their socket(s) then get 'em out of your way.

Once hoses are disconnected and weight of tank is on your support, then, he he, try to slide the tank off of the fuel filler neck. This part might be the most difficult. I have had to disconnect the fuel filler neck from body and drop the tank/neck together before. I have also cut the remaining part of the rubber boot/sea/grommetl before - to get that neck loose.
ALWAYS use a new filler neck to tank grommet - part number 4002010, which is still available new from Dodge (this part fits all FMJ's, and a few other Chrysler products).
4002010 Gromment.png

Note, there are two different grommets with same part number. The above is one version. Either version (tapered or squared) will work fine.
The grommet needs to be installed in tank first. Use of a little something to lubricate the filler neck is advised, when inserting neck into tank.

BudW
 

Kramer79

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Always nice to have good lube when inserting things into openings. Sorry, couldn't resist. :p
Haha - yes that was actually my toughest part, getting the fuel tube into the new grommet - I sanded it with fine grit, then used oil on it… holding and twisting the whole tank to get it back on was the toughest part. Also if I remember correctly the back nuts have those cheap almost threaded washer clips, if they do break then it’s sawzall time. I went rock auto new tank and straps, when you see the inside of an old tank, rarely worth it. I also sprayed the outside of the tank with a can of silver I had around… for the tank top I used a thin plastic foam sheet, like under a laminate floor type thing so no moisture is retained, but it’s not metal on metal when you crank the straps down. I also got a new fuel pick up as the old was was disintegrating… but now my gas gauge barely works! Good luck! Gas vapors are extremely flammable, so any cutting even near an empty tank… careful!
 

slant6billy

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With the exception of the gas door difference on the M body, the F body (later 77 and newer) is practically the same. Check out the removal and new install on the 79 as reference:
 

M_Body_Coupe

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If you do end up disconnecting the fuel filler tube from the body of the car (I find that to be the far easier way to get all this done), check the availability of the following gasket at the local Mopar dealer:

4185037 GASKET, Filler Tube to Wheel House Panel

This is a foam (don't remember of closed or open cell) that goes between the plastic cup the filler neck attaches to and the body panel (sheetmetal).

Let me dig up the Part Book scans and I'll attach, it's item #6 in that diagram.

MOPAR_gask_tank_1.png


MOPAR_gask_tank_2.png
 

Hayzoos

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I had a hard time finding protector strips for between the tank and the straps. I found entry door threshold weather strip or garage door bottom weatherstrip works great. It may hang over the sides of the strap a bit but can be trimmed if you want, a little extra is good though. A little tape around the front, back, and middle of the strap and strip keeps it in place as you assemble.

Most tanks are anti-corrosion treated. Painting or other addition finish can help keep the corrosion at bay. I had once used a zinc (galvanizing) silver paint on a tank. I never got to see if it worked well because the car was totaled before one winter season's road salt could be administered.
 

Mikes5thAve

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The last new tank I installed I clear coated so it wouldn't get any of the brown flash rust type stuff on it. That was maybe 17 years ago and still good.
 

compubert

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I typically use 80lb felt "tar paper" when the tank goes back in, non absorbent and allows some creep of the bands when tightening - and you can trim the excess off with an exacto knife or utility blade. Just try not to scratch the finish on the tank any more than you have to so it wont rust.
 
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