Part Seven: Let’s Tow Something

Project Looks. Muscle. Longevity has come a long way since coming off the used car lot last November. This truck was somewhat high-mileage with 117K on the clock, but it was in perfect condition both inside and out. The previous owner had taken good care of it and Carfax showed great maintenance reports for the first five years of its life. This go-around, we’ll finally make the 2012 Silverado tow-worthy.

During the warmer summer months this truck will spend most weekends in the mountains dragging a 12,000-pound fifth wheel travel trailer around, but to do that it’ll first need an in-bed hitch system installed. For ease of install for a DIY kind of guy, the CURT EZr Double Lock underbed hitch is a great choice. Yes, it’ll still take a couple hours to complete the task, but it can be done start to finish by just one person thanks to CURT’s carriage bolts and their simple, no-drill, no-weld frame rail mounting brackets. There will need to be a big 4-inch hole drilled in the center of the bed floor, but CURT makes this easy, with no measuring required, thanks to the ingenious Center Locator tool included with the kit. The EZr Double Lock offers additional peace of mind and security with a dual locking pin design through the turnover ball.

To meet the towing needs this truck will see in the summer months, an in-bed gooseneck hitch from CURT Manufacturing is going to be installed. The Double Lock EZr hitch system offers easy one-person installation. Thanks to the Center Locator it requires no measuring, uses carriage bolts wherever possible and requires no welding, no sheet metal cutting and no bed removal—the perfect DIY hitch kit.
The unique ball design interlocks into the under-bed hitch brackets using two lock pins for extra security. The Double Lock EZr offers a 7,500-pound tongue weight limit and a 30,000-pound gross trailer weight capacity, more than double what this truck will be towing on a consistent basis.
To help make installation quicker, CURT developed this Center Locator that is inserted into the ball location of the under-bed bracket before it’s installed under the truck.
The boxed frame makes installing the required frame bracket bolts a little tougher on 2011+ GM trucks, but CURT came up with a simple solution. The bolts can be threaded into the coiled wire tie and easily fished through the frame rail from the inside.
The inside of each frame has a large hole that the wire can be inserted into and fished to each outer bolt hole. The large mounting bolts can then be pulled into place and the wire tie removed so the brackets and flanged nuts can be installed. It’s a simple solution and no extra holes will need to be drilled.


Once the frame brackets and under-bed hitch bracket have been installed and all the hardware torqued to spec, it’s time to cut that big hole in the bed floor. From below you can use a 3/16” bit to drill through the center of the previously installed Center Locator. This will place the hole right where it needs to be in the bed with no measuring required.
Once the small hole was drilled from below, we used our drill and a 4-inch hole saw from inside the bed to cut the required hole. Once you’re through the sheet metal the orange Center Locator will be revealed and can be removed.

On 2011+ GM model trucks the toughest part of this install is dealing with the boxed frame rails, as four large bolts need to be fished into place from the inside through some access points not directly behind the outer mounting hole locations. For this, CURT also helps make installation easy by including coiled fish wires you can thread the bolts into to help fish the bolts into place.

With the gooseneck hitch taken care of, in conjunction with a fifth wheel adapter the truck can finally start being used for its real purpose in life, heavy towing. Before that first big camping trip, however, bolting on some additional load support can not only help ride quality and prevent excessive suspension sag when towing but also prevent excessive sway and make for a more stable driving experience.

While on-board airbag systems have their advantages, there are some airless systems available like the SumoSprings kits from Super Springs International. SumoSprings were developed to enhance the load-carrying ability and help stabilize heavy loads for better driver control and ride quality while offering maintenance-free use for the lifetime of the truck. With traditional airbag kits it’s not uncommon for small air leaks to develop in lines or the bags themselves. Over time, an on-board electrical air compressor could need replaced after excessive moisture or use burns it up.

Using a unique micro-cellular urethane, the SumoSprings act much like a large bump stop with a progressive spring rate that helps handle the additional weight and dampen the ride for better stability while driving. The biggest difference between SumoSprings and airbags is how the air is captured and used within the bag. A standard airbag is much like a balloon, trapping air within it, where the air pressure used controls the spring rate. The SumoSpring captures millions of small air pockets within its urethane material. They can’t leak and can be compressed to 80% of their original height and still rebound to factory form.

We determined the two-piece Rebel kit in the mid-density would be best for this daily driver and weekend tow rig. Super Springs offers three different SumoSpring variations, each having three different densities to fine-tune the load support based on the weight you’re pulling and how often you pull it. The Rebel kit works great on a daily driver since when unloaded the travel won’t be limited because the axle is still working independently from the frame. Because the upper and lower pieces don’t require air pressure and don’t ride on each other, unloaded ride quality is unchanged. But as the weight from a trailer is added the two pieces will meet each other and start to compress, offering better support and helping to dampen the ride more effectively than the factory leaf springs and shocks could on their own.

Located next to the center ball hole, the safety chain U-bolts will need holes drilled to be inserted through the bed as well. Again, this can be done easily without measuring by drilling from below through the under-bed hitch bracket and finishing off from above.
The CURT mounting kit required all the hardware and small springs to be inserted on the safety chain U-bolts to keep them from rattling and pulled tightly against the bed floor so they won’t obstruct the use of the bed when the truck is not towing.
Finishing off the installation, the ball release pin handle is installed. The nice chrome trim ring for inside the bed is mounted and the Double Lock EZr ball is installed. When not in use the ball can be inverted, leaving a nice flush bed floor.
When towing a fifth wheel or gooseneck, the trailer wiring harness is often just draped over the tailgate and plugged into the factory connecter at the rear bumper. The harness rubbing on the painted tailgate is less than ideal and often it can bind up on tight turns. To resolve all this, CURT offers easy piggyback harnesses that will add a second connector inside the bed.
To mount the in-bed 7-pin connector a 2 1/8” hole is drilled inside the bedside. On this particular truck the rearmost bedside support is the perfect spot, as it offers enough space behind to fit the plug and harness pigtail without rubbing the outer bedside.
The included self-tapping screws make mounting the connector super simple. Drilling the hole in the bed with a hole saw, securing the connector with a small impact driver and connecting the harness at the bumper took less than ten minutes.
To help with ride quality and load support when towing, the rear suspension will be improved by replacing the factory bump stops with the Rebel SumoSprings kit from Super Springs. The factory front bump stops will also be upgraded with units from Super Springs as well.
On a 2011+ GM truck the lower control arms are limited in travel by a small bump stop on both the front and rear sides of the control arm at the frame. Replacing the factory front bump stops with the SumoSprings system can not only improve ride quality due to the progressive spring rate, but reduce and help stabilize body roll and sway felt from towing a heavy load.
With the factory bump stops removed (right) you’ll see how much physical difference there is with the SumoSprings. The real science is held within the molecular structure of the microcellular urethane, as it allows a progressive spring rate and can rebound to full form even after an 80% compression.
On the rear of the truck the stock bump stop (right) is removed from its mounting bucket and the upper piece of the Rebel kit will mount in its place. The lower piece will be hard-mounted to the axle. The beauty behind the two-piece Rebel design is that it won’t limit travel and the axle can still work with leaf spring travel as needed, maintaining factory ride quality.
The kit for the GM trucks uses an ingenious upper bracket system that basically clamps itself around the factory bump stop buckets. Using this design makes installation simple and there is no drilling required. Once the vehicle is placed back down on the ground, at ride height the bags should have around a quarter-inch gap between them. This allows for great unloaded ride quality but plenty of support when the suspension is loaded down and hauling heavy.
The lower male piece uses supplied carriage bolts, spacers and axle bracket to mount securely around the axle. When ordering from Super Springs you’ll see that they offer three different colors: black, blue and yellow. Each has a different stiffness and capacity. For this application we’ll be trying both the black, which is best suited for vehicles that are always loaded (i.e., welding rigs, tow trucks, snow plow/salt trucks), and the blue, which will most likely be the permanent choice as it offers better unloaded ride quality but still great load support for occasional heavy towing needs, like our 12,000-pound fifth wheel.


CURT Manufacturing

Super Springs International

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