G30 box van build

[DesertDiver4]

Hi everyone, I posted this in the full size domestic section, but I'm thinking it would be better here. I have been reading this site for a while, wanted to start a thread to document my g30 build. It's a surplus airforce radio van, with the 6.2l diesel. 23,000 original miles. First thing I'm going to need is new tires I bought a set of 16" rims to make the tires selection better than with the original 16.5s. Anyone have any suggestions on tire size, and the best AT tire for this truck? I'm thinking bfg at ko2 in 235/85/16 right now, but I'm open to suggestions. I'm going to be doing some offroading with it, and eventually will want to put a locker in it, maybe do a 4x4 conversion at some point, but that would be a long way off.

 

[borison]

Looks like a nice blank slate. Looking forward to your build.

 

[tgreening]

I'm not a good judge of wheel openings but based on my Ford, the 235/85r-16 will fit, but that's about as big as you'll be able to go without modification of some sort.

Huge pass through. That thing is ripe for some seat swivels up front. Jeaaaalous....

 

[DesertDiver4]

I have also been thinking about swivels up front but I'm in the early stages of planing the layout, want to get it on the road and take some test trips with it first. Is there a easy way to see what gearing it has in it? The 6.2l doesn't seem super powerful, with so much load, and I don't want to put tires on it that are too big with the current gearing.

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[tgreening]

Easy answer is usually the door sticker will have axle codes that will tell you factory gear ratio.

Hard answer is that sticker is long gone and you crawl under and look for a tag on the axle that will have codes you can decipher.

Hardest answer is you pull diff covers and start counting teeth. Or a semi-accurate way is jack the rear end, rotate a tire one full rotation and see how many times the driveshaft rotates.

 

[DesertDiver4]

I'll check the door Jam tonight and see if it has something

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[mezmochill]

Size is perfect and you've got the side door and a pass through.

This is about the perfect shell.

Have fun!

 

[UHAULER]

My friend had a similar van, it was a 1975. He put a manual 4 speed it in with 285/75/16 on the back and 235/85/16 front. He lifted it a little bit with some heavier/ longer front coil springs and some wrecking yard rear springs.

 

[DesertDiver4]

Cool van, why did he go with different size tires?
No sticker in the door jam, doesn't have a glove box, just a little compartment on the engine cover, no stickers there. Tried to get the axle codes last night but its infested with black widows under there so I'm going to have to get some spray this weekend and check under there better.

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[UHAULER]

Cool van, why did he go with different size tires?
No sticker in the door jam, doesn't have a glove box, just a little compartment on the engine cover, no stickers there. Tried to get the axle codes last night but its infested with black widows under there so I'm going to have to get some spray this weekend and check under there better.

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There wasn't room in the front for the 285's

 

[DesertDiver4]

Got some relatively new, used tires on the van, went with 245/75r16 they fit fine I think I could even go bigger without any issues. I decided on used tires because I didn't want to buy new ones and change my mind on the size a year from now, this way I can get it on the road while I'm building it. Couldn't find any axle codes under the hood, got the underside sprayed so I'm going to climb under there today and see what I can find on the axle.

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[DesertDiver4]

Jacked up one rear wheel and marked it and the driveshaft for one Rev of the wheel I get ~2.1 revolutions on the driveshaft, does that mean I have ~2.10 gears? Does that seem right?

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[DesertDiver4]

Nevermind, I answered my own question, looks like I have 4.10 gears, have to spin it twice with only one wheel in the air. I guess that explains why it seemed like pretty high revs on the freeway, I should probably either go with lower gears or get bigger tires, right? How hard is it to change the gears in one of these?

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[tgreening]

Nevermind, I answered my own question, looks like I have 4.10 gears, have to spin it twice with only one wheel in the air. I guess that explains why it seemed like pretty high revs on the freeway, I should probably either go with lower gears or get bigger tires, right? How hard is it to change the gears in one of these?

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Doing gears is a tried and true by-the-numbers technical project that is determined to be voodoo science anyway. IOW getting it right can be a real hit or miss endeavor, in spite of following procedure to a T. Around here farming that out will run you about $500 for quality gears and install kit and another $400-$500 in labor. The way I see it is that is money WELL spent because you probably don't have a drop out center section which means you'll be doing all your trial and error laying on your back under your rig. Ive got close to $4,000 in mine but I used top flight parts, put lockers front and rear, and for a change let good sense dictate I should farm that project out.


You should probably look up the stats on that 6.2 and find out where it's rpm happy place is re HP/Torque and go from there. Mine came with 4.10 gears which as I recall made it a bit high in the rpm dept on the highway, but it gave me a bit more low end grunt. Not enough btw because my junk clocks in at about 10.5K rolling, and the idi was struggling after the 4x4 conversion. Considering my 37" tires I went with 4.88 gears, which put me within about 100 rpm of where I was before the bump up in tire size, and turbo charged the silly thing hoping to pick up some grunt while still keeping the gearing within reason.


Anyhow, I think smart move on the tires till you figure out your end game. No sense spending top money on good rubber you might not keep.

 

[DesertDiver4]

Doing some more research I think I need a gear splitter, or maybe do a trans swap to one with overdrive. Peak torque on this engine is 1850 and I would like to get my freeway rpm closer to that, it screams on the freeway right now. I might still do the gear swap but I'm not sure if I would need it if I got the gear splitter or od transmission. Gear splitter seems nicer but if I do a 4wd conversion I'll need another transmission anyway, right? So maybe I need to consider that. Anyone know how possible it would be to do the 4wd conversion without buying the $2500 kit, it seems like a crazy amount of money for what it is.

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