Difference between gas tanks?

My kid has an 80, D100 stepside. /6, A833OD. Pretty clean, he (overpaid) via EPay out of Mississippi. but one issue with it, is that its gas tank has a split in it, the PO put some kind of tar like goo on it to "get it down the road". The problem showed up just before the kid parked it for the Illinois road salt season, he started seeing a "drip" on the driveway.
Anyways we have been looking for a gas tank for it since. this one has the longways tank, between frame and driveshaft. The only tank I have found within a sorta reasonable distance, from a 72-80 has been modified, someone modified it and put an aftermarket float/sender into it so I passed. Ive been able to find a few for (as the interchange at the junkyard says) '81-87 D/W series.

2 different optional capacities aside (in the 81+ trucks), a 20 and a 30 gallon, what is the difference between the "correct" tank for the '80 vs the '81-up? Is (are) the difference(s) enough to keep me from putting the '81-87 tank into the '80 frame? Filler neck location within tank, ohm differences in sender throwing the factory gauge off, shape/size of the straps,etc? If there was an ohm difference in the sender, would the original sender from the '80 fit right, in the newer tank?

don, on facebook a guy named mark c. reeves has 2 tanks for 78 truck. it is under 72-93 truck section. 1 frame tank and 1 rear tank. hope this helps

Located where? I see you are also in Illinois
Where is this Facebook guy?
I don't do Facebook, never have. have to have the kid look that one up.
I picked up a tank from an 84 today, got while the gettin was good. I hope, anyway.

So do you guys know what if any differences in the 84 tank vs an 80 tank?
Also the kid's is a step side. Does THAT make a difference? Vs a sweptline?

brackets probably. look on caar-parts.com and look for tank.

The in frame tanks came in (2) sizes - 18 gal and 20 gal. If you're looking at a 30 gal it's gotta be the aux rear tank. The difference between the 18 and 20 is the shape of the nose. The 20 is square and the 18 has a big recess to clear the transfer case. With a short bed regular cab 4wd there is no way a square nose 20 gal will fit. My short bed reg cab 2wd LRE also has the 18 gal tank and I don't know that it has to have it. I will say that if the square nose fits it would be real tight against the cab floor.

The biggest difference with the early 80s tanks is the dome for the vent and roll over valve. Pretty sure the fuel fill is in the same spot vs 80/down. IF they're taller / wider to sneak a couple more gallons in, it can't be by much because there really isn't that much room under the bed / next to the drive shaft. It seems pretty unlikely that Chrysler would change the straps but can't say I ever really looked.

The easy way to crack a tank is to have it crooked when you're snugging up the straps. If you get the front wedged under the top flange of the frame rail, it will split somewhere when you tighten down the straps. You can melt a split shut with a soldering iron as a short term fix but the plastic is stupid thin in spots and the crack will often come back. It's very often worth the effort to take the bed off and swap the tank from the top. Part of that is the clearance between the tank, the axle and the xfer case. Part of that is about getting to the nuts where the straps attach to the frame cross member, especially the front one. Another option is cut the strap right where the threaded part begins, drill a hole in the strap and use a generic tank J bolt.

Excellent response RWG75 !

While I no longer own one of these trucks, I just learned something from your post.

72-80 long beds could have a 28 gal saddle tank. I have a few trucks with them. I don't think they will fit a short bed.
Another option is the Ramcharger 36 gal rear tank.

Have you checked around to see if there is shop that can plastic weld it.

Yes, RWG, great info with pic!

Ive had both an 81 and an 83 LWB that had the 30 gallon tank in them. Definitely NOT mounted behind the axle "Ramcharger style". mounted just like the 18/20 gallon tanks mount.
The particular truck I am needing a tank for is a shortbed/2wd/ so Id be "stuck with" the 18/20 gallon version anyways.
I just got an 85 LWB, have not even looked under that truck yet, to see what tank it has in it.

Went with a mustang tank, partially for availability (all parts can be had right now off the shelf) but more to balance out the weight over the wheels and even out the aesthetics by replacing the old filler location opening with a led turn signal. Can upload more pics if interested in the process. Later
Sergio

This tank has been for sale for awhile, it's just too bad they are so big and not really something people are willing to ship, nor worth the shipping cost.

https://fortcollins.craigslist.org/pts/d/evans-1979-dodge-d100-adventurer-pickup/7065167848.html

Man that is one nice truck , any way to see more of it . Thanks Gary

instead of trying to install the 84 tank I found him (81-87 seem pretty plentiful) he insists "it won't work" and has had the original tank in 3x for plastic welding attempts and it still leaks.... 1st 2 times as soon as he put 5 gallons of gas in, 3rd time he thought all was good for like a week.... I have done plastic welding (no, Im not the one who tried to fix his tank) and it's tough to master and different for various types of plastic.
as an update I had to go to a funeral in Cape Girardeau MO a few days ago. Stayed down there a few days and checked every yard I could find heading east across extreme southern IL and into Paducah... not a dam Chevy so not a one to be found.....

BUMP
Need to find this tank HELP
That one in ft Collins the ad is dead. Anybody know them?
There's 2 79sin local yards both with the much larger tank so no good. Found 2 75sand those are both longness and way different.
Anybody know this Mark c Reeves that was referenced earlier in thread? I don't do Facebook, I had my wife look/ there's like 8,Mark c Reeves, don't know which one had the tànks for sale can't believe this is becoming so difficult