TECHL INE

COMPILED BY VERNE SIMONS EDITOR@FOURWHEELER.COM PHOTOS: VERNE SIMONS, DIESEL POWER PRODUCTS, ROB BONNEY FABRICATION, AND FOUR WHEELER ARCHIVES

CHEVY SQUARE BODY CUMMINS SWAP

I’ve been a fan of the magazine for as long as I can remember. When I was a kid, at the store with my mom I used to grab any and all off-road magazines off the shelf and read them. You can only spend so much time looking at potato salad with your mom. Often, I came home with several of the magazines back when there were a ton. I’m sad that most of those magazines are gone, but I’m glad that Four Wheeler is still here. I’ve never written in with a question but thought I would today.

I’m contemplating building a new (to me) tow vehicle although this is still all hypothetical. Something that I can use to tow my trailer with off-road toys or a camper that won’t break a sweat with a load behind it, and something that I can take down sandy backroads or to the campsite without worrying about getting stuck. I’d really like something that can tow about 10,000 pounds or a bit more with a crew cab for space. I really love the Cummins engines (the 12- and 24-valve 6BT engines) but finding one of those old Dodge trucks that has any life left is hard these days, and the crew cab trucks are expensive or pretty rough. I also like the style of the old GM square body trucks and think that might be the best place to start since they seem to exist as Crew Cab trucks for sale locally with some regularity. So, I think I’d like to build a Cummins-swapped square body Crew Cab but have a few questions.

First, am I stuck finding a used Cummins or can a crate engine be sourced from somewhere? Secondly, what’s the best transmission to use? What about the transfer case? Do I need to find a 4x4 Crew Cab square body to start with, or can I start with a 2WD Crew Cab and convert it to 4x4? Do I need to box the frame? Any insight or ideas would certainly help.

MARK VIA EMAIL

WHERE TO WRITE

Have a 4x4 tech question you want answered in Techline? Drop an email to editor@fourwheeler.com or message us through our Facebook page at facebook.com/fourwheelermag. All letters become the property of Four Wheeler, and we reserve the right to edit them for length, accuracy, and clarity. Due to the volume of mail, electronic and otherwise, we cannot respond to every reader, but we do read everything. You’re not alone in being sad at the loss of most of the many awesome off-road magazines, and you are also not alone when it comes to wanting to build a Cummins-powered square body 4x4. On both topics we agree. We can’t help bring back the other magazines but will keep working hard to make Four Wheeler the best it can be. In regards to a Cummins-swapped square body Chevy, others have had the same idea, making the task a bit easier for you. In the end, it’s hard to deny the classic styling of the square bodies and they are plentiful, which means there are many great sources for parts and more. In order to make this project happen you will either have to be good at fabrication and at finding a deal on good used parts, or you’ll need to have some deep pockets to fund the build, as the price of the components can add up quickly.

To answer your question about sourcing an engine, our buddy Cooper at Diesel Power Products tells us there are a few new and several remanufactured crate Cummins 6BTs available in the aftermarket. You can spend what you want on a new or remanufactured engine at a place like dieselpowerproducts.com or start the hunt for good used parts. You can choose the Cummins diesel best-suited to your needs—12valve, 24-valve, Common Rail, or 6.7-liter—but be warned, we have heard some pretty sad tales about folks buying junk used diesel engines.

For transmission choices you have a couple of decent options, but in the end, you should select based on what route you want to take and what you want your truck to do. If you can source a used engine locally, it may even come with

a transmission that can be serviced or rebuilt. You can choose between one of the reliable and venerable five- or six-speed manual transmissions or one of the heavy-duty automatic transmissions that can be mated to the Cummins blocks. In manual flavor, you can opt for an NV4500 five-speed, a G56, ZF6, or NV5600 sixspeed. As far as automatics go, you can run a built 47RH, 47RE, 48RE, 68RFE; Ford 5R110 or 6R140; or an Allison without any problem. We’d stick to a name you know in the aftermarket to source a transmission, like ATS, Suncoast, or Firepunk, assuming you don’t have a local transmission shop to build you one to suit.

When it comes to what transfer case you should use, that again may depend on your parts source. Here again, the path of least resistance would be to go with the transfer case that came from the factory with the transmission you are running. Another nearly bulletproof and safe option would be to source an NP205, which is likely the strongest transfer case commonly used in trucks like this. NP205s are available in driver-drop (Ford) or passenger-drop (GM) configurations to match the front axle you will use. NP205s have lots of upgrade options from places like Offroad Design and are pretty easy to rebuild.

Speaking of axles, you’d probably be better off with a Dana 60 in front. Either a passenger-drop kingpin-style from a GM or a driver-drop Dana 60 from a Ford (the latter being much more common).

That brings us to another part of your question: Should you start with a two-wheel-drive or a four-wheel-drive square body GM truck? Again, the answer is that it depends largely on what you can find. Ideally, you could get ahold of a GM 1-ton Crew Cab 4WD with a kingpin Chevy Dana 60 front axle and an NP205. But those trucks are rare to come across.

When it comes to boxing the frame on a square body Chevy it’s more than just a really good idea. The frames on these trucks, while beefy, can always use some additional strength and some of the 4x4 frames of this era are known for having weak spots around the steering box mount. Luckily, and getting back to what we said above when talking about 2WD vs 4WD, Rob Bonney Fabrication (RBF, robbonneyfab.com) has steering box outer reinforcement plates for ’73-’87 Chevy K series vehicles, and frame boxing plates for most GM K series trucks built between 1967 and 1987 and Suburbans built between 1973 and 1991. RBF also has frame boxing plates for ’73-’87 C30 trucks with plans to expand into C20 and C10 trucks soon. The company designed these frame boxing plates specifically for trucks receiving Cummins swaps, although many can be modified to be used even if a Cummins swap isn’t the end goal. RBF also has a few other parts available for GM-toCummins swaps including motor mount kits, radiator and intercooler mounting parts, battery trays, and a high-mount alternator bracket kit.

Finally, we love the idea of this build and want to do one for ourselves, too. You should end up with a stylish, solid rig that will tow with the best of them and should last for decades.

REPLACEMENT PADS FOR THE DYNATRAC PROGRIP BRAKE SYSTEM

I’m the owner of the Jeep JK that Verne Simons and I put the Dynatrac ProGrip Brake System on a few years ago for an article on fourwheeler.com. The Jeep is still doing well and stops great, but the brake pads are getting pretty worn down and I would like to get new brake pads that perform as well as the Dynatrac ProGrip did when we first installed them. Please let me know what I should do.

CHAD VIA EMAIL I had to dig into the memory banks a bit on this one. The Dynatrac ProGrip Brake System we installed on your Jeep uses the factory calipers and upgrades the brake rotor size to increase brake performance. So, in theory, stock replacement brake pads from your local auto parts store would work. Having said that, the pads that come from Dynatrac are a proprietary compound, specially formulated to work with the given caliper pressure and larger rotors, so the best idea is to use replacement brake pads directly from Dynatrac (dynatrac.com). These brake pads are very competitively priced, basically costing the same as parts store replacement pads.

One of the nice things about the Dynatrac kit is that the stock wear parts will work in a pinch. For example, if you are away from home on a long trip and need to replace your worn brake pads with what you can find on short notice they can be found at a local parts store.

You can also look at EBC Brakes (ebcbrakes.com), which has brake pad options with different compounds. EBC has been in the business of making performance brake pads and rotors for decades and lists both YellowStuff brake pads and Extra Duty Light Truck, Jeep and SUV brake pads. The YellowStuff is EBC’s flagship top-selling high-friction brake pad for improved braking that offers improved performance. These pads are also smooth and quiet with excellent cold bite coupled with high-temperature fade resistance. YellowStuff may cause more brake dust than stock or Dynatrac pads. The Extra Duty Light Truck, Jeep and SUV pads offer higher than stock performance and are designed for towing and off-road use. They may be some of the longest lasting brake pads available. Both of these performance brake pads for a JK will work with the Dynatrac ProGrip Brake System. FW