Whose rear mounted tank for C20/C25

[rgunlock]

Hi, I've gone through dozens of threads on rear mounted fuel tanks and filler options. While I've gotten a lot of good ideas, the threads I've seen are hard to sort out details.

I've got a 71 GMC C25 that I'd like to convert to side fill versus coming up in the bed 4 feet back (including open tailgate) that it has now. Who makes a side fill tank with mounting flanges for C20/C25 that doesn't have problems with interference with frame crossmembers, bed cross sills, etc.? --Thanks

[rgunlock]

I ask because its my impression that the rear frame rails are different between C10 and C20 and might affect the position of the tank mounting flanges. Vendors like LMC don't seem to make a distinction between C10 and C20 for these and I'd like to get a tank specifically for my C25. I've tried contacting Boyd's Welding for a tank because it looks like a good one, but its listed for C10 and I haven't been able to get a response to my PMs or email through their website.

So what have you used, or what can you recommend?

Thanks, Rick

[Wobpb377]

To my understanding the only major differences are the suspension parts. Heavier duty for the c20 (3/4 ton)

[rgunlock]

Thanks. If that's the case no problem. I was under the impression that the frame rails were taller for 3/4 and 1 ton versus 1/2 ton. If that's the case, the tank mounting flanges would need to be lower to keep the fill and vent pipes above the frame rail.

[Wobpb377]

Hope someone else chimes in as I don’t hVe a lot of experience. Juts what I read and who’s to say all is true on here.

[rgunlock]

Yeah, I've been doing searches more focused on frame differences than what tank to use. Most of what I'm finding indicates that the 3/4 ton frame is thicker material than the 1/2 ton frame, but the frame rail height is the same.

If that's true, I'd think a tank advertised for C10s would work for me.

[toolboxchev]

Originally Posted by rgunlock

Thanks. If that's the case no problem. I was under the impression that the frame rails were taller for 3/4 and 1 ton versus 1/2 ton. If that's the case, the tank mounting flanges would need to be lower to keep the fill and vent pipes above the frame rail.

To my understanding, through this site, the frame rails are the same, they were made of a high strength metal.

[Andy4639]

I don't know about the frame differences but I just did a rear frame tank install on my 68. I used a "no limit' 19 gallon tank with side fill. You have to cut the frame out but the tank comes with a stiffener piece to weld back in. It also gives you the flat plate strips to use but I decided to slide it into the frame and didn't use them. This gives a little more ground clearance.
I had them do the electric fuel pump mod also so if later on I decide to go with fuel enjection.

[Slowboat]

Is there also and additional rear brace for the c20?

[68Gold/white]

rgun,
Be patient, someone here knows, exactly!!! I do not...

[rgunlock]

Thanks guys!

I know that I should have about 3" between the bed floor and the top of the frame rail to run the filler and vent hose as long as the tank lines them up between the bed cross sills. It looked like (from pictures) the Boyd tank fill pipe was intended to point through that space as long as the top of the tank is at the correct level. So perhaps notching the frame like Andy shows might not be necessary although that looks like a nice tank. On my LWB, the tank would be located more forward in the frame with another crossmember behind it. I'd have to get more measurements to see if that "no limit" tank's filler location would work. From memory I'm thinking it would come out very close to the wheel well.

I did find a post from SS Tim on this site that indicates only a 0.07" difference in height, but I'm thinking that refers to the portion of frame below the cab. In the rear where the tank would mount I know it isn't nearly 6" tall.

C10 127"- 6.04" section height, 2.53" flange width, 0.156" thick, 2.98 section modulus

C20 127"- 6.11" section height, 2.46" flange width, 0.194" thick, 3.71 section modulus

I'll keep hunting for info and watching this thread. Thanks again for those chiming in.

[Andy4639]

Rob @ No Limit is a member here and he may would build you a tank wherever you want the fill tube. I know on this tank you have 2 options, either top fill are side. I would think he would be happy to put it wherever you needed it.
Would be worth a call.
(865) 940-1503

[rgunlock]

Thanks! I'm familiar with Rob from years spent on this site, but had no idea he did custom tanks.

[rgunlock]

Originally Posted by 68Gold/white

rgun,
Be patient, someone here knows, exactly!!! I do not...

No problem with being patient on this one. This truck's bed has 4 holes used at some point for fillers, including 2 large ones that used to be for auxiliary tanks. Plus the original in the cab. I want to patch at least the 4 holes in the bed before cutting a new one!