Truck Lifting Techniques - Lift and Separate

We &8217wheeled a mid-1970s GMC with a 2-1/2-inch lift for long enough to realize that we wanted more ground clearance and better approach and departure angles. After several conversations with Scott Ward and Rody Jarve at 4 Wheel Parts Wholesalers, we went with a 4 Wheel Parts 6-inch Genuine Suspension lift.

The kit includes only blocks for lifting the rear, but our original springs were sagging so badly that we added the optional rear springs, which provide about 2 inches of lift and work with a 4-inch block. Generally speaking, as spring arch increases, wheel-travel potential decreases, so a lift is often detrimental to axle articulation.

The stock springs on this truck had sharply cut edges and nothing between the leaves.

New springs can have advantages over old ones, which will help them flex more. The new Genuine Suspension rear springs have rounded ends and Teflon friction pads to help them move more freely.

We had the 6-inch kit installed at the Burbank, California, 4 Wheel Parts Wholesalers outlet. In addition to the springs, blocks, and U-bolts included in the kit, you’ll need a steering correction of some sort. A Pro Comp 4-inch-raised steering arm was chosen for this truck. With any lift and steering correction, the drag link will need to be adjusted to make the left and right turning radius equal. On 1970s GM trucks, Jarve says to adjust the drag link until the pitman arm is 90 degrees to the framerail with the tires pointing straight forward.

The other gotta-have-it in our book when doing a 6-inch lift on these trucks is longer brake lines. Pro Comp DOT-approved braided steel lines were used front and rear, and have plenty of length without drop-down brackets.

We used a 22-degree ramp-travel-index (RTI) ramp provided by Mike Duncan of Four X Doctor to test the travel of the suspension before and after the 6-inch kit was installed. A ramp is a great measuring device for axle articulation and can help you determine what is limiting travel. Notice that we retained the 33x12.50-15 tires: This keeps the tires from hitting the fenders with the 6-inch lift, although it doesn&8217t increase the clearance under the axles.

All of the numbers and details of our ramp testing can be found in the Ramp Test chart. The first item to hit in the rear was the exhaust tailpipes. Once these were cut off, the emergency brake lines held up the rearend. These were disconnected for now, but drop-down brackets need to be installed for safe use of the e-brakes.

The next items we tried on the ramp were Warrior Products sway bar disconnects available through 4 Wheel Parts. These made the single largest improvement in ramp travel and on the trail. We&8217ve found them easier to hook back up than the JKS units available for Jeeps, but we also found a hammer is handy for moving the bar down over the stubs.

The next trip up the ramp showed that the rear shocks were maxxed out while the front ones still had several inches of travel left. The Eliminator XLT shocks that come with the Genuine Suspension kit max out at 29-1/2 inches (for this application) while the Pro Comp ES 3000s (PN 332000) stretch to 32-1/2 inches. Measure your shocks off the 4x4 to compare the lengths on the truck with the suspension at full droop. Also inspect the shock mounts at full droop: If the shocks are cocked in their mounts, they may be limiting travel without being fully extended.

Next, Jarve loosened the front spring clamps by prying the tabs up slightly. Other springs have a bolted-together clamp that allows the spring pack to flex an inch or so. On this truck, loosening the clamps resulted in the 17-point improvement on the ramp, and it was a free upgrade.

Finally, 4 Wheel Parts greaseable leaf-spring bolts were installed. These polyurethane bushings are fluted to hold lube, and the through bolt is drilled and fitted with a grease zerk. These didn’t increase axle articulation, but the stock rubber bushings were shot so the new bushings greatly improved axle control. On the rear of this truck, the bolts hit the shackle hanger at full droop, but trimming the bolt didn&8217t improve the RTI results. Our final improvement on the ramp came through removing the overload spring on the bottom of the Genuine Suspension rear leaf springs. This lowered the cargo-carrying capacity of the truck, but made a significant difference in wheel travel.

After all of the modifications, the truck ramped better with the 6-inch lift than with the 2-1/2-inch lift, but the biggest difference off-road was the extra 3-1/2 inches of clearance under the rocker panels. The improved wheel travel was noticeable in situations like this where the short lift didn&8217t place any load on drooping tires resulting in tire spin. Only in extreme situations did the 6-inch lift completely air a tire.

With the shorter lift, the front bumper grazed this ledge while the 6-inch lift left plenty of room to spare. Running the trail with the 2-1/2-inch lift resulted in the front bumper being tagged and pushed into the fenders on both sides. The rear bumper caught just about everything, and we scored two dents in the lower sheetmetal on the passenger side. With the taller lift, the rear bumper was the only thing we still hit.

The tires stuffed much farther into the wheelwells with the short lift, but this only resulted in the tires trying to remove the fenders. The ramp revealed that the truck actually has more travel with the 6-inch lift, and the suspension and tire combination proved just right for moderate to extreme off-roading.