GMC Topkick 4x4 Expedition rig

Britboaters

Observer
I retired 3 years ago, and my wife and I got a large 5th wheeler and a 3/4 ton Dodge diesel. We live in SC and have travelled Out West over the last 3 years, including Overland Expo, spending about 6 to 7 weeks each trip in AZ, NM, CO, etc. I was getting tired of towing such a large rig (10,000 lbs) and started getting inspired by some of the rigs we saw at Expo.
In February this year we did a 4 week self drive safari in Botswana and Namibia. A Ford Ranger truck, an Alu-Cab "hard top" rooftop tent, a GPS and the two of us had a fantastic time. A complete opposite to the 5th wheel, and such a memorable trip.
So we decided we needed to downsize. We looked at several different ideas, and as usual got lots of inspiration from Expo. Particularly "Rebelzilla", a 4 wheel drive conversion to an Isuszu NPR crew cab. Finally we setted on a couple of key criteria for us - a bed my wife could walk around to "make", and a separate toilet with a door.
This meant ideas such as Lance slide-in camper wouldn't work. So, doing some layouts, we decided a 14 foot long box would be about right.
We looked at 4WD drive options for Isuzu NPR, but felt the truck too small. We then looked at Isuzu FTR, a 26,000lb truck; but finding appropriate front axles, etc got complicated. We really wanted the FTR as it is a cabover design, so great visibility, and the cab had enough space for my wife to lay down behind the front seats.
We finally settled on a GMC C4500 4x4 Topkick. This is a 17,500 lb GVWR 4WD truck. We found a 2007 single cab diesel with 100,000 miles in FL, so nice and clean. WB of 152". For the 14 ft box we need to lengthen the frame to 176" WB, one of the factory options. This will be the first task, when I get the truck this weekend.
After studying the GMC Upfitters manual, I believe I can move the axle back, and lengthen the frame behind the axle, rather than cutting the frame.
Some statistics:
GVWR 17,500 lb
Chassis / cab weight about 8,300 lbs, to be confirmed
Payload 9,000 lbs
14 ft standard delivery truck box, 150 lbs/ft = 2,100 lbs
Box contents estimate 2,000 lbs
House batteries - 6 x 6v golf cart 500 lbs
40 gallons fresh water 350 lbs
Other stuff about 1,200 lbs, - additional diesel, propane, spare wheel, winch bumper, etc
Total "load" about 6,300 lbs
So total truck weight, with tanks full about 14,500 lb estimated.
Trying to keep front axle load at about 6,250, and rear about 8,250 lbs.
Planning on 335/80R20 Michelins or Contis; so with these weights, 30 psi front, 45 psi rear. This is the recommended pressure for highway speeds !!!
It looks like an offset of 5.5 inches on 11" rims should allow me to use same wheels back and front. Two valve holes will be required though.
Planning on 3 point mounting of body using some rubber bushings I found at a company called "Lord". This will require a subframe to be added to the standard box.
So, I'm posting all this here cause I think it's a good idea to "give back" a little to the Forum, as I've got so many good ideas here.
Also I'm very interested in any help I can get along the way.
So I'll be posting photos as I make progress, and reaching out for help, please.
Hope some of you find this interesting
Bob
 
Your weight numbers are underestimates, possibly by a factor of up to 2.0. Only 40gal of fresh water? You should at least double that. My chassis weight was 6200kg. (Kg, not lb!!) The truck now weighs 12600kg completely full - 612L fuel, 440L water, spare tire plus unmounted 6th tire, batteries, generator, winches, front bar, recovery gear, tools, spare parts, camping gear etc etc.

Charlie
 

Britboaters

Observer
Thanks Diplo for the link. We thought hard about a Lance camper, but one of the major criteria is a walk around bed, as my wife has back issues. We're planning a Murphy bed, so the space will double for a table during the day.
Thanks Charlie for the feedback, but I don't think I'm far off. To be confirmed, when I get the current utility bed off the truck, at a local scale.
I'm trying to get the total well within GVWR. I take your point on water. 80 gallons would only add about 350 lb. My problem is fitting everything in the box, while keeping the weight off the front axle. I have built a spreadsheet to figure out C of G and axle loads. We'll see what the actual chassis cab axle loads are, then go from there.
Thanks
Bob
 

edlaffoon

Adventure Every Day
I take your point on water. 80 gallons would only add about 350 lb.
Bob

Not trying to be contrary but water really depends on your consumption. you may not need 80 gallons, on the other hand you may need 180 gallons. Do you know how large your current tank is? How much do you usually consume? What type of toilet will you use? How long are you planning on going between fills?

If you are smart with the sink/shower, and use a water-less toilet you could easily get away with 40 gallons for 5-7 days between fills.

Everything else seems nice and round, but i always add about 10-20%. I don't think you will exceed your GVRW though.

I'm excited for you man, the Top Kick/Kodiak is one of my absolute dream rigs.
 

Britboaters

Observer
Good questions Ed.
We don't have any data on water usuage. It's all compromises. In a fixed size box, more water means less something else...
We're planning a traditional toilet, and low flow showers, etc.
Once we get the box, and start mocking up the layout, we'll see how much space is available.
So far the project exista as a bunch of spreadsheets, and diagrams. One of the points of posting on here is to get the benefit of a lot of collective experience.
However, I really do want to stay as light as I can, within a budget.
"More light" should mean less stress and cost.
Thanks
Bob
 

DiploStrat

Expedition Leader
Was not proposing the Lance, per se, only noting what had been done with a Topic.

N.B. Two adults, showering daily, cooking, etc., use about ten USG per day. That is taking Navy/military/camper showers. So the questions are:

-- How long do you want to stay out, and,

-- How clean do you have to be?

The truck in the avatar had a ten USG tank and a two USG Coleman jug. Two of us crossed the Sahara. But we like our current 40 USG tank a lot better.
:)
 

superbuickguy

Explorer
I love that you're going to post this in this forum - but you may also want to check this forum http://forum.expeditionportal.com/f...EarthRoamer-Global-Expedition-Vehicles-Unicat for ideas as well. Most of the people there built their own rig thus their results and solutions fit well with the blueprint you're planning.

you said something - that you enjoyed Africa - are you planning on take this to Africa? How will you get it there? any thoughts on the near or far east? Russia? How about air conditioning? generator(s)? solid waste? I'd lean towards the 2x planned - but that's because I'm not a planner and it's basically what's always happened with my rigs. It's obviously not you, and you clearly plan far better then I ever have....

have you read the Turtle Expedition stuff? they've built several rigs just like what you're planning - really neat people too... https://turtleexpedition.com/
They also freely answer questions (don't you love it when someone volunteers someone else that they've only met a couple times in passing?)... while their solutions aren't your solutions, not having to reinvent the wheel when your solutions parallel can be pretty cool as well.
 

Britboaters

Observer
Buick,
Thanks for idea of the other forum, some good reading there.
We're really thinking of US, CA & MX right now, who knows in the future.
We're planning a sizeable solar system, 3 large panels, to give about 2+ kw-hours over the day. With 6 - 6volt batteries and all the controllers / inverter we should be able to be independant, we believe. This is quite an expensive system, over $3,000 total. We are currently planning a simple window AC unit in the back wall, but should probably consider something more efficient from somebody like Sun Power technologies, although cost is a factor. Not planning on a generator.
Regarding "solid waste" - We're thinking tradional black water system. I'd like to go with a translucent tank so I can see the level, but my wife is not impressed. I said we could hang a curtain around it; then she was even less impressed !!
We've spoken at length with the Turtle folks and got lots of good ideas.
I'm flying to FL today to pick up the truck. Then we'll start on stretching out the WB, and extending the frame at the back.
It will be great once we get the truck and body, so we can plan the storage space under the box. There's a lot to get under there, such as additional fuel tanks, 1 black and 2 gray water tanks (one each side), propane storage, house batteries, and boxes for tools, straps etc, space for folding chairs, BBQ and so on. Hoping I can find a fuel tank I can fit behind axle, between the frame. And also would like to put an ASME propane tank between the frame rails, but have read about issues in filling it, and also how can I see the gauge ?
Does anybody know a wrecking yard, preferably in the Southeast where I can find a factory fuel tank for the rear ?
Thanks
Bob
 

DiploStrat

Expedition Leader
...
Regarding "solid waste" - We're thinking tradional black water system. I'd like to go with a translucent tank so I can see the level, but my wife is not impressed. I said we could hang a curtain around it; then she was even less impressed !!
...

For what you are planning, I would strongly recommend a Natures Head composting toilet (which is what we had) or a cassette toilet. Both are much, much easier to deal with outside of the US. Friends of ours, whose truck has traveled to over 55 countries still use their black tank, but with a macerator pump.

Propane can be an issue for shipping and filling, especially in Central and South America. With as heavy a truck as you are planning, you may want to consider diesel and electric appliances. If diesel, using a small, dedicated tank so that you can run on kerosine can help with altitude. We mostly use an induction cooktop - clean, fast, doesn't heat up the cabin. About the only thing it doesn't do well is simmer rice.
 

superbuickguy

Explorer
Solar power. I have 200 watts of panels on the top of my suburban and run a Rooftop Coleman Mach 8 low profile air conditioner off the panels. You cannot have enough panels, and with a/c unit itself. I got lazy, my original plan was to build a unit for the suburban (we do K9 Search and Rescue so the dogs need to be kept cool - but we also live in Seattle so cool only for 3 or 4 hours a day with a fan or two for the balance). The Mach 8, though 'only' 10k btu is way too large for the Suburban so this winter I'm going to do what I originally envisioned. With that said, 5k btu is about right - and that's what you're suggesting using to cool a space at least 3x larger in volume. You can run the a/c unit off solar but there are a whole bunch of caveats to doing so. With 2, 100 watt panels (24x48 each), you can generate enough power to run the a/c for 3 hours every 2 days. Outside of that, you'll be running a generator. Eventually I'm going to do what a very insistent person said is impossible (well, the running the a/c was impossible to start, but this was doubly impossible) and that is downsize the system but then run all of it off an electric pump from either a Volt or a Leaf a/c system.

The key is comfort level. For what I'm doing, it'll work fine. I live in Seattle so a 20 degree temp drop is more then adequate. SC or the desert SW, you'd need far more. Also recognize that efficiency through better insulation pay dividends on several levels. Another thing to consider is that while black is fashionable, silver is cooler.

the tl;dr is this - insulate well, and talk to an HVAC tech for sizing of the unit.
 

Britboaters

Observer
Thanks for you comments and suggestions.
I picked up the truck from Orlando Thursday. While driving home, on I95 near Savannah, I was rear ended by a semi, and pushed across the lanes into woods on the median.
The truck I believe is totalled, hood smashed, axle torn loose, and spring hanger torn off, windows smashed, and so on. Luckily I'm good, just a little sore - WEAR YOUR SEATBELT ALWAYS !!!
There was a 6 inch gap between the utility bed and the back of the truck. The bed hit the truck hard and put a crease in the back of the cab. There is now a 6 inch gap between the bed and the cab again. Amazing there is so much movement possible between those 2 items.
Anyway, there's one less GMC Topkick 4x4 vehicle to choose from now for this project.....
The truck will be probably be written off, but may well be repairable. If i buy it off insurance I'll get a Salvage title, I assume. When I convert to an RV and re-title does anybody have any idea if the new RV title will be "clean" or still show salvage please ?
Also, how do I post photos please ?
Thanks
Bob
 

Paddy

Adventurer
Dang that sucks. I guess it's lucky that it happened now before all the work of conversion.
 

edlaffoon

Adventure Every Day
Wow that stinks, I'm glad yall are ok. No matter what you will probably forever have a salvage title, and rightly so as that is what the vehicle probably is now.

There are a lot of photo hosting websites. I use photobucket but I have a very old account so it's still free for me. Others use imagur etc. You upload your photos to those sites then copy the "IMG" link into your post.

Don't give up, I was really looking forward to this build. I'm sure you will work it out.
 

Britboaters

Observer
Well I'm back. The insurance totalled the truck, as expected, although they've not given me a salvage value for it yet.
4x4 Topkick & Kodiak are hard to find, in good shape, without some very expensive power company bucket or something on the back.
I've found a 2003 C4500 Topkick 2WD near me in exceptional condition. The WB is about right for a 14 foot box, so that saves some work. Odometer shows 15,000, but the rear tires seem to be original and are well worn, so I'm guessing 60,000 or so. It's Duramax, 300 hp with a 6 speed ZF stick shift. But the guy want's a premium for the mileage, and won't accept it's probably bogus; oh well.
So if I bought this truck, and the wreck, I could pull the xfer case and front axle from the wreck. The xfer case should bolt into the frame, in the "stock" position, after new holes are drilled. The xfer case is divorced, so need a drive shaft from transmission. Original OEM driveshaft will fit front, and an original OEM will fit the rear. The axle should bolt right in, although I will have to swap the springs to get the 8,000 lb axle rating. The 4WD switch should be easy to wire in as well.
The 2003 truck have no emissions issues, and the truck I've found has the 300 hp Duramax.
The axle ratios are 5.13, so in OD 6th gear on the ZF transmission, and 335/80R20 tires, I'll be at 1950 rpm at 60 mph. That should be fine.
I got the original GM build sheets for both trucks. They show the weight of the 4x4 chassis cab at 7,950 lbs, so pretty much my original estimate. So my target total weight with all fluids should be about 14,500 lbs. The GVWR of the truck is 17,500, so that should be good.
So if I can cut a deal with the insurance, the project will be back on next week !! First thing is to go to Savannah to pick up the wreck, after Irma passes by.
Does anybody want parts from a 2007 Chevy Topkick - Duramax, Allison 1000, etc, etc.

By the way we'll be at Overland East representing "DriveBotswana", a self drive safari company based in Southern Africa.
Please stop by and chat.

Bob
 
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