Truck Arm Suspension Design: 67-72 C10 Suspension Upgrades

Once we got the cab off our 1968 C10 truck project, we found a clean original shortbox frame with one glaring flaw; a nasty modified rear crossmember. This tipped the scales for us in favor of our 1967-1972 Chevy C10 G-Comp Rear Suspension kit. Not only does this kit come with fresh crossmembers and truck arms to repair any damaged or rusty original components, it also adds a ton of adjustment options. Follow along as we show the and talk through a few tips and tricks to help you along the way. But first, let's take a step back and talk about Chevrolet C10 suspensions.

But there’s more to the story than that. These trucks also left the factory with suspensions, engines, and drivelines that are still up to the task when called into duty in modern traffic. Unlike some contemporaries, GM utilized a fully independent front suspension and a “truck arm” rear suspension that was so good it was used in NASCAR until very recently.

It’s worth noting that we’re obviously talking about ’63-’72 Chevy trucks. Though there was a body redesign in ’67, much of the chassis and suspension was very similar for those years from ’63 until the birth of the Squarebody in ’73. Since the above video highlights progress on our ’68 C10 project, that generation will be the focus of this article.

One interesting note about the dynamics of this setup is that there is some anti-roll geometry built in to the design. To understand this, think about an early Ford rear suspension with a torque tube. Since there’s a lone pivot point at the back of the transmission, there is no resistance to either side of the rear axle moving up or down (besides shocks and springs, obviously). Then, think about the extreme at the other end of the spectrum. A T-Bucket with a pair of radius rods that extend straight forward from the housing to the outside of the frame. With the front pivot of the rods so far from each other, the entire housing must twist in order for one side to significantly rise or fall independent of the other. So, with the C10 setup, that short distance between pickup points at the center crossmember adds some roll stiffness to the rear, without producing a huge bind as in the T-bucket scenario described above.

It’s also worth noting that the panhard bar, or track bar, can also be used to dial in the suspension. The stock car guys got really good at panhard bar adjustments that would plant the rear tires on an oval. The G-Comp C10 Rear Suspension that we installed in the video above offers multiple panhard bar pickup points to allow adjustment not available in the stock setup.

Quite simply, the truck will sit lower if you replace the stock height rear springs with lowering springs. But this will only get you halfway there. As you approach 5 inches of drop, things start to get wonky with the stock geometry. In particular, the panhard bar will be running at an odd angle and the shocks will be laid down enough that their travel and function will be adversely affected. Speedway Motors offers a rear lowering kit that corrects both situations with a new track bar and frame-side mount as well as new shocks and shock mounts. This is the right way to do a budget drop. And don’t forget the C-notch.

We went one step beyond with our ’68, as detailed in the video above. We replaced the truck arms and springs with new pieces as supplied in our G-Comp 1967-72 Chevy C10 Coilover Truck Arm Rear Suspension Kit. This kit comes with new truck arms to replace rusty originals, a new crossmember, and new brackets for the truck arms that allow multiple mounting points and will allow us to dial in the instant center to increase forward bite. It’s also worth noting the cool cams that make it possible to align the rear suspension. As we alluded to earlier, the panhard bar and brackets in this kit also have multiple points of adjustment to further dial things in. Finally, as the name suggests, this kit also allows us to upgrade to coilovers that will really help us nail the stance.

It's now time to start mocking things up. As you’ll see in the video, we installed this kit twice. Once in bare metal and primer to make sure everything fit and to weld up our panhard bar bracket on the axle side (the only welding required on this kit) and once after everything was welded and painted. We installed the crossmember first, followed by the truck arm brackets, truck arms, and 9” axle housing. We took the opportunity to check pinion angle and install some shims. This will be fine tuned once the truck is on the ground and at ride height.

With everything installed, squared, and at ride height, it was time to attach the panhard bar bracket to the axle housing. This is a good time to double and triple check your measurements. We had to cut a notch out of the bracket to work with our 9” housing, but your results may vary. Regardless, be sure to have this welded by a certified welder. There is a lot of force on this bracket.

With the bracket welded and all components mocked up, it was time for paint and reassembly. It’s worth mentioning that when you get to the coilovers, the clip the holds the spring cup on the end of the shock can be a bear to get on. Everything else fell together and all brackets and crossmembers aligned perfectly with the holes in the stock chassis.

Now, we can’t wait to get the rest of the truck together so we can start fine-tuning our G-Comp rear suspension!