1959 GMC Adventure Bus Build

baipin

Member
Being dismayed by rent prices, liking a bit of adventure, and a good project, I decided to buy a bus in the summer of 2020. I'm a guy in my late 20's, finishing up school, on the way to working as an elementary teacher and planning on living up in northern Ontario's more remote communities in this thing, and traveling in the warmer months.

I was initially planning on a Thomas C2 4x4 owned by Schlumberger as a wellhead maintenance crew transport... but that went for many times more than it was worth at auction, so I figured I'll just build my own 4x4 bus. How hard could that be for your first 4x4 build, right? 🤪 So, I ended up with this guy from Saskatchewan:

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Basically rust free by Ontario standards... It's just surface rust, and way less than anything I could find over here that was only 10 years old.

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Got working on an interior buildout while I waited for the bus to get here. I'll be living in this thing full-time. Details have since changed but the overall layout remains the same.

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Took delivery of the bus in late August of last year. The curved glass was all intact, which was a nice surprise.
Found out it had a 283 small block, and it runs well, but, the plan has always been to swap to a mechanical diesel. I'm not looking for great fuel economy, but 4 MPG as it was, is terrible...

I began by removing the front axle and fabbing some offset shackles to fit new 47" Chevy springs (2.5" to the original 2" hanger). Yeah, the spring are kind of short, but this is budget build, and for a bunch of reasons that involved weird curves in frame, and a shackle hanger integral to the front crossmember, I could not put shackles at the rear and opted to keep them up front. The front will have air assist.

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Railroad track makes a great press punch 😎

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Got a Dana 60 for the front. Moving the spring mount 1.25" forward makes everything sit nicely.

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baipin

Member
Opted for a Sweet Mfg. servo to give the bus some power steering, but with a hydraulic cylinder between the axle/tierod:

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I eventually painted and rebuilt the Dana 60, and got that under the bus:

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Mocking up draglink length. Since the shackles are at the front, the steering box is behind the axle. This necessitated a custom steering arm:

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I also got a VERY good deal on BFG Bajas + asymmetric 24 bolt H1 wheels and tires. All from 2019. Given that they're two-piece rims, they're easier to work on by myself versus 22.5" OTR truck tires, better bead retention at low pressure, and more road-friendly tread versus other military tires. High enough capacity for my needs, too.

Getting that axle under the bus was brutal on winter nights - the only time I had free to do that work. Stupid me didn't bother to truss/beef it up, so it'll coming out after I free up some space in my shop...

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In the meantime, before I could re-tackle the axle; I finished doing gaskets and seals on this Rockwell T-136-27 airshift case a few days ago, painted it up tonight, but this is how she looked when I got her. Also built an air shifter for high/low range (normally lever operated). This drastically saves on valuable interior floorspace; I'll have two dash-mounted valves now.

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baipin

Member
I finally got a chance to re-tackle the Dana 60 front:

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The inner C's were gusseted on the top and bottom. I researched common failure modes in Oka front axles, since those trucks have a max GVWR in line with my bus. Of those that failed, many had bent tubes and/or bent inner C's. This should fix that. Outers snapping and ring gear failure presumably from extreme deflection of a low-pinion axle in a front application, also happened to a lesser extent. 35 spline outers and a load bolt from Jantz engineering should fix both of those things.

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Before the axle goes in, this guy will first:

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Found a great DT360 runner, locally. Little brother to the DT466. I prefer it over the 6BT, though they're both excellent mechanical diesels. Gave the engine, and the frame, a new paintjob.

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Getting the engine in there was an absolute chore. Very tight fit:

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Don't worry, the gap around the harmonic balancer has since been embiggened... ;)

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That's all for now.
 
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ExpoMike

Well-known member
I cannot give this enough Likes!!! This is sweet and now I want to build on but I have too many projects. LOL Looking forward to the build!!!
 

baipin

Member
The gearbox looks like an Eaton 5 or 6 speed. Please enlighten us.
Yessir. Eaton FS6406A 6 speed with a DT360 on one end and a T-136-27 Rockwell transfer case on the other. 1550 shaft to the rear, 1410 to the front. 63:1 crawl ratio with 3.54 gears.

Got the transmission for next to nothing because the previous owner thought he damaged it in a rebuild. Turns out he just forgot to install the brass shims on the output bearing retainer... Took them off and threw them all away, I guess.
 

baipin

Member
You’re going to make a great teacher!


Sent from my iPad using Tapatalk
Thank you, I'm excited!


Thanks! I have a Dana 80 that I was planning on using. The problem with this is it's about 69" wide from wheel surface to wheel surface. Not wide enough for Humvee tires as is. I'll have to either use spacers (e.g. Stahl Steel) or recenter my humvee wheels. I'm confident I could fabricate a safe, well-balanced recenter. Spacers are both more expensive and seem more prone to failure from what I've read. Thoughts?

If I decided to sell the Humvee tires, that'd open me up to 22.5 OTR tires, which would let me put a massive rear end in there and dramatically increase GVWR if need be (an identical frame was used in Chevy Viking 40 and 60 trucks up to 15,900lb payload/25,900lb GVWR).

As it is, the bus has a two-speed 15,000lb axle with unworkable ratios... 6.40 high 8.72 low, and I don't think higher gears were ever made. 1.66" shafts 12.75" ring gear.

The Dana 80 has a 11.25" ring gear and 1.50" shafts by comparison. Still rated for a higher GAWR than I'll ever need with Humvee tires run as singles on the rear, but if you can think of any larger rear ends that could accept a 16.5" wheel I'd be interested. All I can think of is the 11.50" AAM with 12.00" AAM gears.
 
What’s your estimate of total fully loaded weight and weight distribution? Remember that whatever you estimate, add ~20%
What’s the gvwr on the vehicle?
My guess is that something with more load capacity than 37x12.50R16.5 would be good.
 

baipin

Member
What’s your estimate of total fully loaded weight and weight distribution? Remember that whatever you estimate, add ~20%
What’s the gvwr on the vehicle?
My guess is that something with more load capacity than 37x12.50R16.5 would be good.
These tires have a 4,540lb load capacity, so they're more than sufficient as the "weakest point" I think. Curb weight is approximate, but it should be between 9500lbs and 9700lbs as a shell with the engine, trans, t-case,axles; everything but the interior conversion/solar. This is based on a 8,720lb bus nearly identical to mine, with a similar body and axles - just with a 460 gas engine, E4OD, and BW transfer case versus my DT360, FS6406A, and T136. Estimate for water and fuel is 500lbs. Estimate for water is 500lbs, fuel 360lbs, tank 40lbs. Therefore 10,000lbs to 10,200lbs curb. Therefore 10,400lbs to 10,600lbs curb. (edited numbers).

I expect the interior and solar to weigh 2000lbs-3500lbs With a 20% increase, that's 3500+700=4200lbs at the max. (Just did some calculations and suspect a weight of 2400lbs; 2900lbs with a nominal 20% increase).

Therefore, the bus - fully converted - should come in between 12,400lbs and 14,800lbs. I do not know the actual GVWR because tags are missing, but I'm designing everything around an a 15,000lbs goal.

I expect FGAWR to be 6,500lbs, RGAWR to be 8,500lbs. These numbers came from not wanting to overload the tires on the rear (technically I could go as high as 9080lbs and remain within spec) and not overload the low-pinion front axle. I know the low pinion 9.75" Dana 60 ring and pinion is used in front military applications up to 6500lbs by Dynatrac. I will have a load bolt in mine, however, which dramatically reduces deflection under the most severe conditions (from 0.030" to 0.003"). The way I've trussed my axle, should make the axle housing itself stronger than the 7000lb rated F550 Super Dana 60. I used FEA to model this, so I'm fairly confident in those numbers.

Do you think an estimate of 2000lbs to 3500lbs, not counting the 20% addition, is accurate? That seems in line with weights for skoolies and long wheelbase sprinter conversions from what I've seen. It's a 17.5'x7.5' interior, FYI.
 
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Maybe, but your numbers are still a bit low. The drivetrain difference alone is more like 12-1300 lb. The trans alone is 360 lb.
. Don’t know how many people you’ll have but I carry 440L = 966 lb water in my 16’ camper. Fuel is 7.2 lb/gal, you’ll want 60-100 gal so more like 1000 lb for fluids. Maybe 3000 lb for interior is safe.
You’re pretty obviously not looking for a speed demon that will cruise at 75-80, correct?
I’m very subjective re tires but for something like this if you like bad roads, and need to go briefly offroad sometimes to be out of sight at night, “ideal” for this size/weight category would be 335/80R20 (~40-41”, 5000-6500 load capacity, speed limited to 68mph).
In my mind to maintain good offroad mobility one should be below 75% tire max load rating. With all the crap on tends to carry (in my case, recovery gear and since my chassis is a unicorn spare parts and tools) weight climbs.
Went over your numbers again. You’ll be at ~14000 before adding all the extra stuff. Since you’ll presumably stay in North America tools and parts and recovery gear might be as little as 500 lb. But still very close to tire capacity in rear and as long as you’re confident in front axle capacity…I’d look for a rear axle with capacity 10-11000. Like Earthroamer axle capacities. I really really like your drivetrain choices (motor, trans, TC).
 
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baipin

Member
Maybe, but your numbers are still a bit low. The drivetrain difference alone is more like 12-1300 lb. The trans alone is 360 lb.
. Don’t know how many people you’ll have but I carry 440L = 966 lb water in my 16’ camper. Fuel is 7.2 lb/gal, you’ll want 60-100 gal so more like 1000 lb for fluids. Maybe 3000 lb for interior is safe.
You’re pretty obviously not looking for a speed demon that will cruise at 75-80, correct?
I’m very subjective re tires but for something like this if you like bad roads, and need to go briefly offroad sometimes to be out of sight at night, “ideal” for this size/weight category would be 335/80R20 (~40-41”, 5000-6500 load capacity, speed limited to 68mph).
In my mind to maintain good offroad mobility one should be below 75% tire max load rating. With all the crap on tends to carry (in my case, recovery gear and since my chassis is a unicorn spare parts and tools) weight climbs.
We talking 75-80 kilometers or miles per hour? ;) If miles, absolutely not! If kilometers, yeah, I'll take it on backroads around 80km/h or 50 mph. Class 8 trucks are speed limited to 105km/h up here, so I have little reason to go faster than them on the freeway...

The 335/80R20's look great. I just don't know where to find MPT81's up north here, let alone for a decent price. Interested to see what shipping would cost to the border though... I usually get tires from militarytires.ca but they don't have any options in the 40-43" sizes at the moment, that are also light enough (i.e. not 300lbs per wheel/tire combo).

You are correct, I missed half of my fluids. I had 60 gal. of water at exactly 500lbs. Fuel was another 50 gal. at 360lbs. but I may bump that up to 70 gal. at 500lbs. So, bus weight would be between 12,800 and 14,900lbs.

I'll definitely be carrying tools, so a 15-20% increase in total conversion weight is probably fair.

The Earthroamer (Dana S111, S130, etc) axles are excllent choices, though the hubs and brakes are simply too big for these wheels. I'd use one if I could. The Dana 80, if sticking with these tires, is definitely sufficient. The guy who sold them to me offered to trade them in for something else if I wanted to go to 20's in the future. In that case; finding 20" wheels for the front are is also an issue. Though I suppose I could use aluminum MRAPs, an adapter plate, and then cheap steel 20's for the rear to keep costs down, since tire wheel weight is a lot less of an issue there. With 20's, I could increase my rear GAWR massively and I'm sure there's something at the local truck yard worth using.

Thank you for all the tips - highly appreciated!
 
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