1942 MB Rolling Chassis - Project All-AmericanPosted in How To on May 1, 2002 Comment (0)
Project All-American is finally rolling. It took a lot of phone calls, a fleet of UPS trucks, and a great degree of patience from all involved parties, but our '42 MB is standing on its own four feet (Metaphorically, of course. They're actually a kickass set of Goodyears). For all of you who've been following the stories involving the buildup, you'll know that we'd previously had a front Dana 44 built by M.I.T. in El Cajon, California, and a rear Tera60R built by Drivetrain Direct in Corona, California. Both units came together smoothly and have been anxiously awaiting a frame to reside beneath and a set of springs to support them. Once we had all the components on hand, we set out for the Four X Doctor in Burbank, California, to bring everything together.
While the actual setup of the rolling chassis didn't really take all that long to carry out, the process leading up to it did. There was the matter of ordering the custom frame from Matkins Extreme Jeep Frames and working out the details of its construction. We spoke with Alcan Spring in length regarding the custom leaf spring design, all the while involving M.I.T. and Drivetrain Direct to ensure that we'd achieve the accurate pinion angles and spring perch widths. With that all said and done, hanging the springs on Revolver Shackles and bolting up the 37x12.50R15 Goodyear MTs mounted to 15x10-inch MRT bead locks was a cinch. Look to the sidebars in this story for more information about ordering custom frames and springs for your 4x4, and check back next month for another stage of the All-American buildup. Stars and stripes, folks. Stars and stripes.
Custom Frames: The Big Picture
A frame is a frame is a frame. Think so? Think again. While every vehicle frame serves relatively the same purpose, as a structural piece functioning as a bridge between two axles, a number of critical factors levy into the strength and quality of each frame. These critical factors include material, the amount of material used at the stress points, and geometry. Mild steel is the material of choice in boxed frames, which have been used by Jeep since 1976. The amount of material used is most easily determined by looking at the cross section of steel in the frame.
This figure relies on rail height, rail width, and rail wall thickness in order to be derived using a formula we'll list below. As for the geometry of a boxed frame, the only factor of major importance is internal leverage, which can be figured by dividing the vertical dimension of the framerail by the wheelbase. In the case of a stock CJ-7 frame, where the wheelbase is 94 inches and the rail height is 4-1/2 inches, the leverage factor is 0.048. The leverage factor is directly proportionate to rail height. For comparison purposes, we can also factor a relative strength coefficient. This is done by multiplying the leverage factor by the cross section.
For a stock CJ-7 frame with a cross section of 2.08 to 2.13 inches, this figure is 0.101, a much lower number than the 0.167 achieved by the Level II Extreme Matkins frame constructed for Project All-American with its 2.98-inch cross section. One element that changes this number drastically is that when a frame is bent (as opposed to cut and welded), the cross section reduces at the bend, resulting in a significantly lower number, depending on the radius of the bend. The metal can also become fatigued at the corners, allowing the geometry of the tube to be compromised by partial collapsing and making the tube even weaker than the cross section and leverage factor figures may reflect. Cross-section and leverage factor are as important to a frame as cubic inches, bore, and stroke are to an engine.
The manufacturing process of a frame is another important factor in its strength. There are three common processes for making box tube frames. As we previously mentioned, the bending method has the disadvantage of weakening the structure at the bent areas. In mandrel-bent applications, pieces of metal are inserted into the tube to limit collapsing within the tube. This method requires more material than others but is still advantageous in that it's more economical and has a smooth appearance. The fastest process, a process used by most major automobile manufacturers, is the platen-forming method where two pieces of flat stock are pressed into a C-channel and welded together face to face to form the box tube. The strongest and most labor-intensive process is the cut-and-weld method, in which each section of rail is cut to the desired length and welded to the next cut section in line.
This method is required by NASCAR and is the primary method used by Matkins in the construction of its heavy-duty Jeep frames. There are other methods as well, such as hydro-forming and impact-bending, but these are the most common on the market.
So with all of that churning through your head, what more do you need to know to order a custom frame? Not much. Matkins keeps it simple by asking just a few questions of prospective customers; year, make, and model of vehicle (the company now offers early Bronco and FJ40 frames in addition to its Jeep lineup), preference of bent or welded construction, how you use the vehicle (competition or trail use), and modifications desired, such as extended wheelbase, custom suspension setup, and so on. After filling in the blanks, you should be just a couple weeks out from having your custom frame in hand.
Matkins Project All-American Extreme Jeep Frame Dimensions:
Wheelbase: 79 in
Vertical dimension (rail height): 5-1/4 in
Rail width: 2 in
Rail wall thickness: 7/16 in (bottom rails); 3/16 in (all others)
Cross section: 2.98 in
Leverage factor: 0.066
Relative strength coefficient: 0.197
Stock CJ-7 Frame Dimensions: Wheelbase: 94 in
Vertical dimension: 4-1/2 in
Rail width: 2 in
Rail wall thickness: 3/16 in
Cross section: 2.08-2.13
Leverage factor: 0.048
Relative strength coefficient: 0.101
Leverage factor (Lf): Lf = H/L
Cross section (Cs): Cs = [2x(H-T) + (2xW)]xT
Relative strength coefficient (S): S = LfxCs
Wheelbase = L
Vertical dimension/rail height = H
Rail width = W
Rail wall thickness = T
Custom Springs: Easy as Orderin' a Pizza Pie
For those particular applications where off-the-shelf products just won't cut it, custom leaf springs are the solution. Since we were carrying out a fairly extensive vehicle buildup, we decided that this was one of those applications and contacted Alcan Spring to meet our needs. The company suggested a Wrangler-style spring because it's a proven design and would greatly increase our off-road ability from that of the shorter and skinnier stock flatfender springs. Since we were already ordering our custom frame with a few mods, we had the staff go ahead and reposition the spring mounts on the frame to accommodate the longer springs.
The new springs are constructed of 5160 high-carbon spring steel and were custom-built for our application, taking vehicle weight and type of usage into consideration. The company features a seven-leaf pack with extra torque leaves in the rear packs that measure 25 inches from eye to eye. Alcan offers a build sheet so customers can list in detail the components of their vehicles to better determine overall vehicle weight and describe their level of usage. As always, more information is better than less since the springs are custom-made for each vehicle, and the less variance in vehicle weight the better the springs will operate.
Another item to keep in mind when ordering a custom set of springs is spring rate, or the amount of energy it takes to compress a spring through its first inch of travel. This figure is expressed in lb-in and is the determining factor in how much the spring will compress as load is increased. There are four physical dimensions that can affect the spring rate of a leaf pack: number of leaves, leaf length, leaf width, and leaf thickness. Spring rate can be calculated with the formula listed below.
Goodyear MT/Rs and MRT Bead Locks:
Almost Too Cool for Their Own Good
Daddy needed a new pair of shoes. Shoes with bead-locked laces and plenty of traction. A combination that would dice through sand and loose dirt, climb rock faces in a single bound, and chug through the deepest of mud at negative air pressures without missing a beat. Well, we found 'em. The Goodyear Wrangler MT/R is not only one of the most capable tires on the market, it's also one of the best-looking ones. Featuring a kickin' tread pattern with high, stiff lugs and sidewall grabbers, the MT/R is easily recognizable in any size configuration on any vehicle. With its three-ply sidewall construction and Durawall Puncture Resistance Technology, it's also one of the most durable tires around.
Making it even prettier to look at and ever able on the trail are the 15x10-inch MRT 36-bolt Steel Rockcrawling Wheels. MRT has been making bead-locked wheels for more than 20 years and hasn't stopped improving upon them since. The 36-bolts ensure that the tire bead won't slip off the wheel even when running ultra-low air pressures. The wheels are available in a variety of sizes, including custom applications. We opted for the black steel D-window design.