1973-1987 GMC Suspension Buildup
From the June, 2009 issue of Sport Truck
By Kevin Lee
Photography by Kevin Lee
We started with the rear suspension....
We started with the rear suspension. We removed the bed from the truck to gain better access to the rear suspension and the area of the frame that was going to be cut. We removed the rear bumper and disconnected the electrical wiring and gas fillers. The eight bolts were removed; two of which had to be ground off at the head because they were spinning in their holes. To make the job as easy as possible, we removed the tailgate and the wheels and tires and lowered the frame as low as it would go on the jack. That done, just two people were easily able to lift off the bed.
Once the truck was jacked...
Once the truck was jacked up again, four jackstands were placed under the frame: two at the rear and two in front of the front spring mount. The four jackstands must be used in this manner to avoid stress to the frame while it’s being cut. With the jackstands in the proper position, we slowly lowered the rearend housing so that all the tension was off the springs. We removed the shocks and then the U-bolts that held the rearend to the leaf springs. It&8217s not necessary to remove the rearend completely; just lower it at this point. Be careful not to overextend the brake lines or the driveshaft.
The front spring bolts were...
The front spring bolts were removed from the spring hangers, then the rear spring bolts were removed from the spring hangers. The leaf springs were lifted out and set aside. Our truck has a GVW of 10,000 pounds, so it has the eight-spring pack with the overload. We were initially going to reuse them by removing a few of the leaves, but after inspecting them closer, we discovered a couple of broken ones. We decided to get a new set from Detroit Eaton Spring.
A template is included with...
A template is included with the flip kit instructions. It must be cut out and used as a guide to mark the frame in the area to be cut.
Before we could mark the frame,...
Before we could mark the frame, we had to remove the stock bumpstop. It&8217s held in with a rivet that we ground the head off of, and then we knocked the bumpstop loose with a hammer. The template is marked with a guide hole that corresponds to a hole in each framerail. Line up these holes and scribe around the template.
We then drilled a 1/2-inch...
We then drilled a 1/2-inch hole at each corner of the inside radius of the cutout. This allowed for a gentle curve at the corners to prevent stress cracks at the end of each cut.
We moved the brake lines and...
We moved the brake lines and electrical wires out of the way, then used a grinder with a small cut-off wheel to carefully cut along the marked lines. It’s important to take this slowly so you don’t cut too much. Don&8217t do this with a cutting torch; that will change the temper of the framerails.
After the edges were deburred,...
After the edges were deburred, we slipped the C-notch insert over the framerails by gently tapping the insert with a hammer and a block of wood. The left framerail’s lower edge had a rolled lip that wouldn&8217t let the insert slide on all the way, so we had to trim a little more off that edge. Once that was done, the insert fit right. Eight 1/2-inch holes were then drilled through the frame--six through the side and two through the bottom--to bolt on the insert. Once the holes were drilled, the supplied bolts and Nylok nuts were installed. With the C-notches secured, we installed the new urethane bumpstops.
The new Detroit Eaton Springs...
The new Detroit Eaton Springs leaf springs came with urethane bushings that we easily pressed in with a C-clamp.
The rearend was raised up...
The rearend was raised up to the framerail. We installed the new four-leaf pack springs from Detroit Eaton Springs under it, using the original hardware.
The saddles were then installed....
The saddles were then installed. We made sure the locating-pin hole in each one went toward the front, per the instructions. The U-bolts were slid down over the axle into the spring plate, and the Nylok nuts were installed. We tightened the nuts slowly, alternating from one to another to ensure they were evenly tightened. The rearend should sit in the saddle but not touch the bottom. If the gap is greater than 1/8 inch, trim the saddle taps to get the proper fit.
We finished the rearend with...
We finished the rearend with a set of KYB shocks from Performance Suspension Components (PSC). The only extra hardware we had to get were two shorter bolts and narrow Nylok nuts for the lower shock mounts. This was necessary because with the flip kit, the U-bolts came right down along the outside of the mount, which allowed the longer bolt to hit the U-bolt.
With the rearend done, we...
With the rearend done, we moved to the front suspension. We disassembled the entire front suspension and then cleaned each part with some Marine-Clean from Resto Motive.
The control arms along with...
The control arms along with the new urethane bushings from PSC were taken to a local frontend shop to have the old bushings removed and the new ones installed. The upper arms&8217 cross-shaft nuts were removed, and the bushings were knocked out with an impact. The new bushings were coated with assembly lube and pressed in. The old ball joints were removed, and new ones were bolted in their place.
The lower arms&8217 bushings...
The lower arms&8217 bushings were even harder to remove. After 20 years of road grime and moisture, they had become almost welded in place. To remove them, we burned out the old rubber with a torch and knocked out the metal sleeve by hitting it with an impact.
The lower cross-shafts were...
The lower cross-shafts were thoroughly cooled before the new bushings were installed. Make sure the notch for the crossmember-locating pin in the lower shaft is on the topside of the front of the shaft. The old ball joints were pressed out, and the new ones were pressed in.
The reassembled control arms...
The reassembled control arms were installed onto the crossmember and torqued down to the recommended specifications. Be sure to locate the crossmember pin in the notch on the lower cross-shaft before tightening the U-bolts.
Our Early Classic Enterprises...
Our Early Classic Enterprises 2-inch-dropped spindles and 2-inch-dropped coils were installed onto the lower control arm. Be sure to install the coil with the smaller end up and with the end of the lower coil against the relief in the lower control arm.
We slowly jacked up the lower...
We slowly jacked up the lower control arm and made sure the top of the coil properly slipped around the raised portion of the inside of the crossmember. Once it was in correctly, we pushed the upper arm down and installed the upper ball joint nut to secure the assembly.
Before the suspension components...
Before the suspension components were assembled, they were painted with Eastwood&8217s Detail Gray. Before we disassembled the original tie-rod assembles, we noted how many threads were showing, so we could reassemble the new ones to the same length. This, we hoped, would allow us to get the frontend alignment close enough to drive the truck to the alignment shop. The tie-rod assemblies were installed onto the centerlink, which was then installed.
To take full advantage of...
To take full advantage of our truck&8217s new, tightened suspension, we opted for a rebuilt variable-ratio steering box and a new rag joint from AGR. Every component has to play its part, and if one of them is sloppy, the whole package is going to feel loose. The rag joint, which connects the steering box to the steering column, is very seldom changed and if worn-out can really make the suspension unresponsive. AGR also has new intermediate shafts available with universal joints at both ends that eliminate the rag joint and make the steering ultraresponsive. The downside is this solid connection also transmits all the road feel and bumps through the column.
This truck was bought in Fresno,...
This truck was bought in Fresno, California, and driven home to Los Angeles. After we tore apart the front end and inspected the brakes, it was a wonder to us that it had made the trip. The front pads were all the way down to the rivets, which had already started digging some pretty deep gouges in the rotors. They were beyond the point of rescue by turning, so we contacted Raybestos for a set of its Brute-Stop rotors. We packed the new wheel bearing from PSC with grease and installed them into the rotors.
We liberally coated the spindle...
We liberally coated the spindle shaft with high-temp grease and carefully slipped the rotor assembly in place. The outer bearing, washer, and spindle nut were then installed. The nut was tightened until a slight drag was felt and then backed off slightly, so the cotter pin could be installed.
Rebuilt brake calipers were...
Rebuilt brake calipers were picked up from a local parts store, and new Street Legal braided-steel lines and bleeder valves (which allow one-person brake bleeding) from Russell Performance Products were installed. We also installed new carbon-metallic pads from Southbay Motorsports, which come with the edges chamfered to help quiet them.
Here&8217s the truck before...
Here&8217s the truck before we did the work.
The "after" shot shows a noticeable...
The "after" shot shows a noticeable difference. Not bad for a weekend’s work. The truck now has a slight bit of rake and a much lower look without being so low that it&8217s impractical. Now all it needs are some new wheels and tires.
No system on your truck affects your driving enjoyment more than the suspension. You may have a 500hp big-block under the hood that can roast the hides, but if the suspension is loose and unresponsive, the truck is going to be miserable to drive. On the other hand, if it handles like a slot car, you can have an anemic six under the hood and still have a blast tearing through some twisties with your foot on the floor.
When it was time to freshen the suspension on our '77 GMC 1/2-ton shortbed, we decided to set it a little closer to the ground and tighten it up with polyurethane bushings. Our truck had a GVW of 10,000 pounds, so it rode a little firm and sat kind of high. We decided to go with a 4/6 drop and contacted Choo Choo Customs for a flip kit. We used a C-notch from Belltech in the rear and 2-inch-dropped spindles, and 2-inch-dropped coils from Early Classic Enterprises (ECE) took care of the front.
To ensure we'd get the kind of handling we wanted, we turned to the experts at Performance Suspension Components (PSC) for a complete rebuild kit, including graphite-impregnated polyurethane bushings and a set of KYB gas shocks. For the steering box, we turned (pun intended) to the knowledgeable people at AGR. They rebuild and customize a wide variety of boxes--everything from stock replacements to ultraquick 12:1 boxes. We opted for one of the company's variable-ratio sport-valved boxes.
We set a weekend aside, and with the help of a few friends, we soon had the truck torn down and back on its way to road-warrior status.
4920 Rondo Dr.
Performance Suspension Components
Belltech Sport Trucks
2822 E. California Ave.
Choo Choo Customs
7801 Lee Hwy.
PO Box 1235
Early Classic Ent.
5843 E. Clinton Ave.
Russell Performance Products
225 Fentress Blvd.
263 Shoemaker Road
Southbay Motorsports Design
14664 Deon Dr.