The ’73-’87 GM truck (’73-’91 for Blazer and Suburban) is the Jeep of the fullsize truck world. There is an incredible amount of aftermarket support for this GM 4x4 platform, which includes our ’85 1¼-ton military CUCV pickup. When it came to attacking the suspension of our fullsize truck project, the sky was the limit. Everything from complex and expensive multilink coilover suspensions to bolt-on soft-ride leaf packs are available. We decided to keep our truck durable, simple, and easy to replicate. This will help us avoid some of the common issues which are frequently associated with overly pliant suspension systems such as steering problems, axlewrap, and driveshaft binding. Originally, we thought we could fit 40-inch tires with only 4 inches of lift, and it can be done. However, our 18/39.5-15 Interco Super Swamper Bogger tires mounted on 15x12 Eaton beadlock wheels from National Tire & Wheel are a little wider than most, so they would have required quite a bit more fender trimming, and likely would have necessitated the removal of the inner fenderwells. We wanted to retain these because they hold the factory dual battery tray and other underhood components. Sticking with the overall simplicity theme, we bumped up the lift to 6 inches. All of our suspension mods were bolt-on, with one minor exception. Here is what we assembled on our CUCV. Keep an eye out for the next installments where we’ll improve the steering and add a few other off-road tricks to our truck.
Step By Step
1. The starting point for our front suspension is a pair of Tuff Country EZ-Ride 6-inch-lift springs and SX6000 shocks. The springs feature urethane bushings and a 465-pound spring rate. Grease the bushings prior to installation. We detailed the front lift with longer stainless braided brake lines and heavy-duty shackles from Offroad Design.
2. Offroad Design specializes in modifying fullsize trucks for off-road use so the new shackles are way stouter than the stock parts, which can bend when abused off-road, especially if they make contact with the trail when dropping off ledges or rocks. The new shackles are zinc plated, include urethane bushings and drilled Grade 8 bolts with grease fittings to keep the suspension assembly moving smoothly and squeak free.
3. With the 6-inch springs installed, our stock steering system was far from ideal. Tuff Country offers a raised steering block for a GM Dana 60 front axle (PN 70102), which will work fine in most street applications, but we plan to upgrade our entire steering system for better performance on- and off-road. We also need to compensate for our ridiculously wide wheels and tires.
4. Always install fresh U-bolts with your new leaf springs. Used U-bolts can be weakened from rust, stretching, damaged threads, and so on. It’s cheap insurance to keep your axles under your 4x4. Don’t forget to cut off the excess threads once they are torqued to spec. A 4 1/2-inch angle grinder loaded with a 0.045-inch cutoff wheel makes quick work of overly long U-bolts.
5. To lift the rear of our GM truck, we opted to keep the factory leaf springs and install an Offroad Design 4-inch-lift shackle flip. This requires the removal of the factory shackle-bracket and rivets. A grinder, air-chisel, or torch can be used. We prefer to use our Miller Spectrum 375 X-Treme plasma cutter that can literally hose away the heads of the rivets. Shackle bolts sometimes need to be torched to be removed. We were lucky, ours simply unbolted.
6. The Offroad Design shackle flip bracket (right) provides 4 inches of lift by positioning the ends of the leaf springs downward 8 inches further than the stock shackle bracket (left). This will alter the pinion angle a bit, and in some cases may require correction. Our truck has a 3-degree wedge installed under the leaf pack that we will remove when making another upgrade later on. This should put our pinion angle close to correct.
7. The Offroad Design flip brackets come complete with all the hardware you need to bolt them to the frame using the original holes as a guide. Several of the holes need to be drilled out to 7⁄16-inch. Keep in mind that some trucks may require new shackle bolts, bushings, or shackles. Rust and age can take their toll on these parts. Inspect them carefully and replace if needed.
8. We finished up the rear suspension with a pair of Tuff Country SX6000 shocks and an Offroad Design stainless steel extended brake line. We had to fabricate an extension for the proportioning valve so our rear brakes would work properly. Since the shackle flip rotates the axlehousing, we had to cut and reweld the passenger-side shock mount for shock-body clearance. A reciprocating saw made quick work of cutting the ends off of our exhaust to clear the leaf springs.
9. We used a combination of tools to trim the inner and outer front fenders. A reciprocating saw and an angle grinder with a cutoff wheel make the heavy chopping easy. An air saw was used for the more precise cuts and a regular old 2 1/2-pound sledgehammer beat portions of the inner fenders out of the way. We still have a bit of trimming left to do to keep the tires from rubbing at full flex when turning. We’ll also need to add some longer bumpstops.