Speedway Motors’ 1968 C10 Build Part 2: Chassis & Suspension

By Joe McCollough – Images by the Author

In the last installment of our Speedway Motors C10 build, we gathered up a derelict ’68 C10 shortbox and dragged it back to our shop. What was left of the old truck was carefully taken apart and the chassis was blasted and treated to a fresh coat of epoxy and black urethane. Now it’s time for the fun part to begin with the install of our G-Comp rear suspension, a rebuild of the front suspension with some new parts for a lowered stance, and an upgrade to the brakes.

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002 G Comp C10 Coilover Truck Arm Rear Suspension Kit (PN 91604054 — The G-Comp C10 Coilover Truck Arm Rear Suspension Kit (PN 91604054) offers several advantages over the stock truck arms, and one of them is the ability to adjust the instant center geometry by moving the truck arm pivot points up and down. This will help us dial in some forward bite when our truck hits the street.

Though our truck wasn’t much to look at, the chassis was exceptionally straight and rust-free. The glaring exception was a rear crossmember that had been crudely torched at some point in this truck’s eventful past. We were eager to get rid of this eyesore, so we elected to start at the rear. We selected the Speedway Motors G-Comp C10 Coilover Truck Arm Rear Suspension kit for its bolt-on installation, improved geometry, and adjustability over the stock suspension, not to mention the addition of coilovers. The fact that the kit included a fresh new crossmember direct from our fab shop that would replace the hacked stocker was icing on the cake.

003 cams that locate the front of the truck arms — Another cool feature of the G-Comp rear suspension kit is the cams that locate the front of the truck arms. These allow for a precise setup when it’s time to align the truck.

Before we got started with the suspension install, we bolted in a Speedway Motors C-notch kit. This kit worked well with the G-Comp rear, requiring only a small hit with the grinder to clear the Panhard bar bracket. The notch kit promised plenty of clearance for the G-Comp’s lower ride height.

004 We set the cams in the center for our mock up — We set the cams in the center for our mock-up. We will fine-tune them when the truck is complete to dial in the alignment.

We were eager to bolt in our trick new suspension, but we had some work to do before we got to the fun part. The factory crossmember, Panhard bar bracket, and truck arm pivot brackets needed to be removed, which meant that the factory rivets needed to go as well. We used a combination of grinding, drilling, hammering, and air chiseling to get ours free. Just remember that those factory holes will be reused with the G-Comp brackets, so don’t let them get oversized or otherwise out of shape.

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005 Truck 9 Inch Housing (PN 91046118) — Time to install the housing. We chose a Speedway Motors Bolt-In ’67-72 Chevy Truck 9-Inch Housing (PN 91046118) and a 9-Inch Clutch-Style Posi Differential Third-Member (PN 91049345).

With the stock pieces removed, we were ready to mock up our G-Comp suspension. Note that we did this before any parts were painted, then disassembled for paint before moving onto final assembly. We started with the new crossmember and truck arm pivot brackets that came with the kit. The G-Comp suspension allows for adjustment to the truck arm pivot points to dial in driveline angle and make instant center adjustments. The same front brackets also utilize some nifty cams to fine-tune rear axle alignment.

006 C notch kit (PN 91006372) — We moved the housing up to ride height to continue our mock-up. Note the considerable increase in available travel from the C-notch kit (PN 91006372).

With the crossmember and brackets installed, we were ready to move onto the axle housing. Instead of spending time and money upgrading the stock axle, we elected to use a brand-new Bolt-In 9-Inch Housing, fully assembled Speedway Motors Third-Member with a 3.50 gear ratio and a weld-on Universal Disc Brake Kit. This setup was sure to handle the power that we planned to throw at it with the added bonus of converting from the stock six-lug axles to the later 5-on-5 bolt circle. Whether using a new housing or your truck’s original, the only welding necessary is the attachment of the Panhard bar bracket to the housing.

007 The 9 inch housing also necessitated a small amount of trimming to the bracket — Next up was the Panhard bar. The bracket on the housing side is the only welding necessary in the whole install. The 9-inch housing also necessitated a small amount of trimming to the bracket to match the shape of the housing where the centersection meets the axle tubes.

Before we made anything permanent, we mocked everything up at ride height and carefully measured to several reference points to be sure we were centered and aligned. We measured 12-3/8 inches center to center on the shock lengths to determine our ride height. We then set up approximately 6 degrees of driveline angle using some angled shims between the housing and the truck arms. Finally, we measured (and remeasured) to be sure the housing was centered. Finally, the Panhard bar bracket was tacked in place.

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008 We mocked the housing at ride height — We mocked the housing at ride height, then measured and remeasured the pinion angle and side-to-side positioning of the housing before tacking the Panhard bar bracket in place on the axle. Note the multiple holes in the Panhard bar brackets to allow roll center adjustment.

At this point, we were ready to pull the rear suspension apart to fully weld the new Panhard bar bracket, cut the stock Panhard bracket off, then prime and paint everything. All that remained was final assembly and we were ready to move onto the front.

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009 we tacked the Panhard bar bracket in place — With all of our measurements verified, we tacked the Panhard bar bracket in place. For ease of access, we’ll wait to fully weld it until the housing is out of the truck. Remember to weld a little at a time to avoid warping the housing. This is a critical part of the suspension, so farm this out to an experienced welder if you’re not comfortable with your welding skills.

Our goal with this truck is not to win at the autocross or lay frame. Instead, we’re after a lowered driver that sits right and is ready for lots of miles out on the road. To reach those goals, we chose a tried-and-true recipe to drop our C10’s frontend and make it stop better, starting with a Speedway Motors ’63-70 Complete Front Suspension Kit. This kit comes with everything you need, down to the nuts, bolts, and cotter pins, to lower the ride height and convert pre-’71 trucks to stock-style disc brakes. In addition to the brake kit, this kit also includes 2-1/2-inch dropped spindles, 2-inch dropped springs, and shocks designed for the lower stance. That combined 4-1/2 inches of drop will be noticeable without being excessive.

010 the stock front suspension as it rolled into the shop — Ugh. Here’s the stock front suspension as it rolled into the shop. We chose a few upgrades to the stock geometry that would help us meet our goal of a dropped truck with better handling and braking than ever before.

We also chose to upgrade to a set of tubular upper and lower control arms. The arms were installed first, followed by the dropped springs. Next up came the spindles, taking care to point the caliper brackets to the rear. At this point the included wheel bearings were packed, seals installed, and rotors slid into place. The brake calipers were installed with the included slide bolts and we were pleased to find new brake hoses were included as well. The kit included new upper shock mounts and even the bolt for the bottom of the shock. With the shocks bolted up, we were ready to wrap up our install. Working with the fresh, new parts from the Speedway Motors kit made this all a breeze and we even surprised ourselves by finishing it all up in a morning.

010 Universal Disc Brake Kit (PN 91031933) — Here’s our rear suspension all painted up and reinstalled. The coilovers will allow us to fine-tune the ride height so we can nail the perfect stance. Also visible in the photo is the Speedway Motors weld-on Universal Disc Brake Kit (PN 91031933).

Power steering was a luxury that didn’t make the cut when our truck was ordered from GM. We decided to make the upgrade using a new power steering box. As a part of the install, we also chose to use a Chevy Pickup Front End Rebuild Kit to freshen up the rod ends and tie rod components. With all of these new parts, about all that was left from the factory steering setup was the centerlink and idler arm bracket, which had to be liberated from the crusty remains of our stock suspension, blasted, and painted. With the dirty work done, we bolted up our new box along with the new rod ends, idler arm, and power steering pitman arm.

012 tubular upper and lower control arms (PN 91036375) — After lots of blasting and painting, it was time to move onto the shiny new parts. First up was a set of tubular upper and lower control arms (PN 91036375). These were fully assembled and ready to go out of the box, saving us hours of rebuilding the stock arms and adding better performance and a trick appearance to our suspension.

Next was the moment of truth. A rolling chassis is always a big moment, and we couldn’t wait to see the results of our altitude adjustment, even if there was no weight on it yet. We bolted up a set of 15×8 front and 15×10 rear Speedway Motors Rally Wheels with some redline radials for that requisite ’60s vibe and dropped the jack. We couldn’t help but grin at the sight of our freshened chassis with a noticeably lowered ride height. Moments like these are what fires us up to keep pushing through the rest of the build, and we were already scheming on a hopped-up junkyard LS engine to drop between the ’rails. Stay tuned as our C10 receives its heart and makes some surprising power!