How to Build a Custom Rollcage with Seating for Eight
Christian Hazel’s M-715 rollcage build review.
Back in 2008, as the technical editor of Jp magazine, I covered the buildup of my 1968 M-715. I purchased the former US Army Jeep as a basket cases in Boise, Idaho, for $800 and turned it into a 400hp off-road 'wheeler and family fun wagon. Most of those stories are online if you search "The Evil Truck" on fourwheeler.com, but unfortunately a lot of the original photo captions didn't transfer with our latest website update. Additionally, I always take way more photos than I need to for any given story, so without the shackles of predefined print space limiting how many photos and how much text I can use, I'm free to expand on the original story of how I built a custom rollcage with seating for eight in this highly popular and capable Jeep.
Even though I originally built the truck with the factory T98 transmission and NP200 transfer case backing a 290hp Chevrolet Performance 350 V-8, I eventually upgraded the drivetrain to a Ranger Torque Splitter, SM465, and 3.0:1 Atlas T-case. The new drivetrain really expanded the truck's off-road performance and increased the freeway speed to the point that it just wasn't all that safe running around with only the low-back buckets and no 'cage to keep your head intact in the event of a catastrophic rollover. Besides, if the big Kaiser Jeep did roll over with the battery box between the recovered factory low-back buckets, you couldn't even dive for safety. I decided it was time for an upgrade in the safety department and a good opportunity to increase the seating capacity to better fit my growing family.
I bought some mini kid-sized Empi Race Trim seats that would fit my smaller kids. For the adult seating, I got four Corbeau Baja Ultra suspension buckets and two Baja Ultra Wide buckets, which are a bit more comfortable for larger people. I didn't really know exactly how I wanted the seats arranged so I set them on the driveway next to the Jeep and sort of played around with various configurations to see how I could most comfortably fit seating for eight. I eventually settled on three rows comprised of two Baja Ultras with an Empi Race Trim in the first row, two Baja Ultra Wides in the second row, and two Baja Ultras with an Empi Race Trim in the third row.
I stripped the factory seat and battery box form the interior. The battery boxes and the sheetmetal underneath them are notorious rust and rot zones on these trucks because it's not uncommon for corrosive battery acid to leak, especially if the truck was improperly stored with old wet-cell batteries. Thankfully, my truck was in good shape with only some light surface rust eating through the hearty military green paint job. Note the wing window glass secured in the factory storage spot with replacement Beachwood Canvas straps.
With the interior completely stripped and swept out, I was ready to start the rollcage build. I decided I wanted as much safety as possible, but I also didn't want to get rid of any of the functional things like opening glove box door, the previous-owner-fabricated sheetmetal storage box on the doors, the wing window storage, and roll-up windows. That meant my cage would need some clever planning that would increase the build complexity, but I did my best to keep it as simple as possible. When building a rollcage, anytime you add a bend, you're adding weakness, so I eventually settled on a traditional front and rear hoop configuration with straight runners, front and rear cross bars, and longitudinal door bars.
Another thing I really didn't want to get rid of was the factory rifle mount. Even though I didn't have an M14/M1A that would drop right in place on this Vietnam-era US Army surplus vehicle, trinkets like these are a huge part of a historic vehicle's character and should be retained if at all possible.
Because this truck was a relatively low-level off-road machine that would see duty on only moderate trails, I decided rather than tie the rollcage straight to the frame, I'd instead use extra-large floor plates with different-sized plates underneath to prevent punch-through. I built my upper plates ridiculously large and using the normal floor plates as templates, traced where I needed to drill my mounting holes.
I drilled the upper plates and punched through the thick M-715's floor and secured the rollcage plates with the 0.120-inch-thick plates on the underside. Simple Grade 8 washers would probably have done the trick just as well, but resistance to punch-through is increased as you spread the load, so bigger is better. Using dissimilar-sized plated top-to-bottom also helps prevent the floor sheetmetal from tearing should the worst happen.
For the same reasons I decided against tying the rollcage directly to the frame, I decided to use less expensive HREW (hot rolled electric welded) tubing instead of DOM (drawn over mandrel) or chromoly. I bought about 160 feet of 1.75-inch, 0.120-wall HREW from my local steel supply company and had it delivered to my driveway.
One thing you have to know if you're planning on working with HREW tubing is which way your bends are going to go. You always want to keep the welding seam on the inside of your bends when at all possible. If you put the weld seam on the outside, it can weaken or even tear open the tubing.
Ideally, I would have converted my bender to an air-over-hydraulic setup, on which I could snug the tubing into the bender and bend it with a pedal on the floor, while keeping both hands on the work. However, my bender is a regular old manual unit, so to keep the hoop propped up and oriented correctly requires three hands. I found that one of my curbside recycling barrels with an angled lid makes a darn handy sawhorse that I can carefully position as needed, along the tubing to angle it up or down to hold it at the proper orientation until I start bending. Once the bending starts, the tension of the bender on the tube more or less holds it in place. It's not perfect, but my results are really good, so it's how I generally work. As for the bender mount, I normally have it bolted down to concrete anchors in the middle of my garage floor, but when I built this cage, I had another unfinished project Jeep sitting in the way. To build a makeshift bender mount, I welded a couple tabs to my trailer tongue and slid the bender between them. I cinched the tabs tight with a bolt and the bender was perfectly stable. I built the rear hoop with a slight dihedral on the downbars, so they came down at an angle to almost meet the body tub and then kicked back in to clear the rifle mount and other impediments, ultimately connecting to the center of the floor plates.
With the rear floor plates and hoop set in place, I built the floor plates for the front hoop. I wanted the front hoop to somewhat follow the angles on the windshield and dash before kicking down towards the firewall. I radiused the corners to avoid sharp angles and employed dissimilar-sized upper and lower plates to help avoid sheetmetal tearing and punch-through.
I built the front floor plates out of two large pieces of 0.188-inch steel plate that I welded together to join the two planes of the floor. To better follow the contour of the floor, I whipped up a makeshift brake in my vise using some heavy-wall 1-inch tubing to contour them as needed to sit flush with the floor sheetmetal. When done, I bolted each side down the same as the rear plates and then started figuring out how I wanted the front tube to run.
The front tube wound up being a heck of a piece of work. I first made the upper bend to kick the tube down at the same angle as the outside of the windshield frame keeping mindful to squeeze the inside of the tube bend far enough out to clear the glovebox door, yet far enough in that the window cranked could still be used. The margin for error wound up being less than 0.120-inch per side, so it really put my bending measurement and three-dimensional thinking skills to the test. Once I got that angle right, I had to put slight bends in the tube roughly two-thirds down the dash to kick the runners both back in towards each and to angle the upper part of the hoop at the same rake as the windshield frame. Then, at the bottom of the dash, I kicked the downtubes forward to meet the floor plates. It's pretty easy to mess up things like this because you've got to build one side of the hoop pulling through the bender one way, and then basically reverse your thinking and bend from the other side of the hoop on the other.
So, in other words, you build the bends for the passenger-side tube from the top-down, but then you've gotta flip the hoop over in the bender to do the driver side from the bottom-up. It pays to stop and think hard about what your bend is going to do and which way it's going to form as the tube feeds into the bender. Once I got the hoop built I chopped the ends to match the angle of the floor plate and tacked it in place, holding the top up with one of the Beachwood Canvas straps at the windshield frame
Once I got the front hoop built and slung into place, I cut our straight runners and tacked them in place to the front hoop. With the front and rear connected I could then focus my attention on the cross bars, longitudinal braces, and then move on to the seat mounts.
The dash cross bar is always a simple one to build and lends a ton of strength to the whole cage system. I often use a 1.5-inch, 0.120-wall tube here because it makes it easier to fit, but honestly, I can't remember sitting here 12 years later if I used a 1.5- or 1.75-inch tube on this project. It was a fullsize with plenty of room, so maybe I used the same tubing as the rest of the cage. Chop the tube roughly 1-inch wider than you need it, notch each side roughly 0.5-inch deep, and boom—a perfect fit every time. I chose to put the dash bar low on this project for several reasons. For starters, its position here is right between two bends, and it's also the only place on this hoop that are perpendicular to the floor, requiring no angled notching (not that that's a big deal). The position allowed easy opening of the glove box and didn't obscure the view of the gauges like a top-mounted bar might.
I build some longitudinal runners that extended along the door opening and kicked in to meet the rear hoop downbars. These bars not only greatly stiffen the cage system, but make a good place to build your seat mounts off of.
The longitudinal door bars tied into the front downbar just above the floor. I kept them relatively low on purpose, so you wouldn't trip over them as you're entering or exiting the vehicle.
Once I was happy with the cage build and had ensured all my notches were tight and the bars were all square, I used an old moving blanket to prevent the wind from blowing my welding shield gas away and burned everything in. Back then, my welder was a 210-amp Hobart Iron Man 220-volt welder (PN: OM-927) that was an excellent performer for anything from light sheetmetal work to building axle housings.
With the front cage mostly built, I turned my attention to mounting the three seats. For the little Empi Race Trim seat, I welded some steel tabs directly to the heavy battery box mount, which worked out really well. I then removed the Empi and worked out a plan to get the Corbeau Baja Ultra seats installed.
A trap I sometimes let myself fall into is being reluctant to mix square and round tube when building a rollcage. In reality, there's nothing wrong with square tubing for seat mounts and, especially in this case, the 1.25-inch, .0120-wall square tubing made it a lot easier to build my bucket mounts. I built short spacers to lift the cross bar over the transmission hump in the rear and then started working out the front.
For the front seat mounts, the transmission hump in the floor was much too tall to simply stretch a bar across from one end to the other, and I really didn't want to cut or dent the tunnel. Instead, I built separate driver- and passenger-side bars off the door runner bars that connected to a tab bolted down to one of the factory seat bracket mounts. It wound up being a pretty simple solution, and the end result was clean and unobtrusive once the seats were bolted in. Happy with the fit after test-mounting the seats, I welded everything together and moved on to the rear cross bar and harness mounts.
The last bar needed for the front part of this half of the M-715's rollcage was the rear cross bar. Originally, I wasn't going to bother building one, but I was using Corbeau harnesses with shoulder straps, and the cross bar made a safe and secure place on which to put the harness mounting tabs. I positioned the cross bar in such a way that the side window and canvas top footman loop strap mounts were easily accessible and then burned everything in.
I wrapped up the front rollcage build by bolting the Baja Ultra buckets, Empi Race Trim, and Corbeau harnesses in a few days before heading out to Moab Easter Jeep Safari. Because the cage wasn't completely finished, and I wasn't sure if I'd still be adding to the front part, I left it unpainted but gave it a good rub down with WD-40 to help keep humidity and rain from flash-rusting the steel. Notice I wound up putting a slight bend in a couple pieces of 1-inch, .0120-wall DOM tubing and welded them in between the front downbar and outer runners. These served as both a grab handle for ingress/egress as well as a gusset to help add strength.
I loaded the M-715 on my trailer behind my 2007.5 Ram Megacab and hit the road from San Diego for Moab. We hit rain around Victorville, and by Beaver, Utah, we were getting snow. At first, the snow was something of a novelty with the kids wanting to get out and catch snowflakes. However, by the time we rolled past Richfield it was really coming down and as we approached Fish Lake National Forest on I-70 speeds were down to about 10 mph in near white-out conditions. We passed several vehicle rollovers and accidents, eventually pulling into Moab just before sunup. What usually takes 3 hours took 10, but oiling the cage paid off, and during all that snow-soaking, the steel remained relatively rust free.
Once back home from Moab, I got back on the building the rear of the rollcage. I built up three identical hoops, each with a slight dihedral and the widest part of the downtubes sitting a tidy 0.25-inch inside the top of the bed. The middle hoop wound up mounting to the top of the inner fenders, which on an M-715 bed are insanely thick and sturdy. I hit the middle hoop with a chop saw to ensure each of the three hoops sat atop the bed at the same height.
With my oldest lending his special brand of help, I drilled the thick steel of the bed to accept the foot plates. As usual, I used large foot plates to help punch-through and backed them on the underside with plates, nuts, and washers.
Once I got the M-715 bed floor drilled, the hoops were loosely bolted in place, and I turned my attention to building the stringers to connect them.
Although seemingly simple, when you're taking four separate pieces of tubing and attaching them via notches to curbed pieces of steel, it's easy to mess up an angle and make the cage look out of square. Using some spring clamps, I took a lot of time to ensure the bars were not only evenly spaced, but aligned horizontally. Don't forget to take the time to step back and inspect your work from a ways off from different angles. Once again, as soon as I was happy with the placement of the tacked tubes I burned the joints together with my Hobart and moved on to the daunting task of fitting the five seats in the bed.
Because the M-715 is a truck, and I did at one time use it to haul heavy loads for my avocado grove, I wanted the ability of keeping the bed for utilitarian uses if the need arose. Because of that, I built a subframe onto which the seats mounted. The seats and harnesses mounted to the subframe, which was securely fastened to the massively thick M-715 steel bed floor. By removing eight Grade 9 mounting bolts, I could slide out the whole seat assembly and load the bed. If I needed even more hauling flexibility, I could unbolt the rear rollcage and use the bed to haul whatever I needed. At least, that was the theory. In reality I never did remove the seats or the rollcage.
To allow enough legroom for adult passengers, I wound up pushing the second-row seats just between the wheel tubs. The Third Row just spilled over the top of the rear tub. I used this vehicle for countless parades, birthday parties, and outings at max capacity.