Factory shocks on pickup trucks are usually a compromise among a number of disparate factors. The price the original equipment manufacturer pays is one factor, as is passenger comfort and how well they hold up when people use the truck.

The 2015 GMC half-ton used for this upgrade story was as top of the line as you could get in 2015 without opting for the Denali package. As fancy as it was, the shocks felt underdamped, especially in rebound. It would handle small bumps OK, but larger bumps really unsettled the truck.

Another rub was that it came with P rated tires. The P stands for passenger car, which isn’t very truck like, nor is it ideally suited for towing, which is one of the reasons people buy trucks in the first place. Duh.

The owner upgraded the wheels and tires to E load range LT, which underscored how bad the factory shocks were, so it was clear the suspension cried out for an upgrade, too.

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We went with Bilstein 6112s for the front, which come with springs, and can be adjusted to four different height settings. For the rear, we went with Bilstein 5160s, a monotube shock with a piggyback reservoir, and we upgraded the clamps that hold the reservoirs. We also added a three-quarter-inch lifting block to the rear axle to raise the rear for towing.

It’s about a thousand-dollar upgrade, but the result was worth it. Towing a trailer is no longer a white-knuckle affair. Large bumps and undulations no longer unsettle the truck, and the ride is well damped with or without a trailer attached. It’s now buttery smooth with a trailer in tow.

A couple of tips on the installation. The fronts are coilovers, and the new shocks need the factory top hat, which means you need a spring compressor to do the job. Do not rent one and attempt to do the job yourself. That’s how people lose fingers and eyes. We took them to one of our favorite local shops, Superior Brake and Alignment in Santa Barbara, Calif., which specializes in alignments and suspension work. We had them swap out the front top hats — and everyone still had fingers when we were finished.

The rears would have taken about 20 minutes, but because we were adding three-quarter-inch lifting blocks, we had to jack up the truck by frame, remove the rear axle from the leaf springs, which was a heavy, clumsy exercise. Luckily, there are locating dowels and holes on the leaf spring, axle and the lifting block, so when everything goes back together, it’s in the right place. We did the blocks first, then installed the new shocks, but you have to remove the lower shock mounts to install the lifting blocks.

This would make for a great winter project to upgrade a truck. Come race season, all the wrench time should go toward the racecar. Here’s how the project unfolds.

The front upper shock mount is retained with three nuts on the studs for the top hat. There’s a few wiring harnesses running across there that snap onto the studs. Just pull them off and remove the nuts.
To get the suspension to droop enough to get the shocks out, you’ll need to remove the sway bar end links and bushings. The end link spacers are plastic, so there’s a potential for a future upgrade here, too.
The lower front shock mount is held in place with two bolts that go through the lower control arm and into stamped steel retainer nuts.
The Bilstein 6112 at right reuses the factory top hat. You can either rent a spring compressor — watch your fingers! — or take the assembly to a nearby shop and pay them to swap it out. We opted for the latter. Note the four adjustable height settings on the bottom of the Bilstein shock tube.
Even when the guys at Superior Brake and Alignment did the job, it took two of them on a proper spring compressor tool. Seriously, you can lose a finger removing preloaded coilovers. Just pay someone to do it right.
To keep the shaft from spinning as you torque the top nut, grab the flat sides of the shaft with a crescent wrench and torque the Nylock nut with a gear wrench.
Here’s the new assembly ready to go back into the truck. The Bilstein lower mount doesn’t use the factory nuts. It comes with new nuts.
With front suspension at full droop, the new shock drops in from the top, down through the lower control arm, then back up into the upper mount. Thread the nuts onto the upper studs to hang it in place, then get the lower mounts into position.
With the new hardware, torque the lower shock mounts. It might be necessary to go through and “nut and bolt” the front shock mounts after a few days of driving to ensure everything stays good and tight.
Torque the upper shock mounts and snap the wiring harnesses back onto the studs. Right and left are the equally easy to access. Now it’s time to move to the rear axle.
The 5160 rear Bilstein shocks come with piggyback reservoirs. These are the upgraded brackets that cost a little more than the band clamps that come with the shocks. Before you install the shocks, tighten the clamp to hold the reservoir, but leave it loose enough that you can rotate the reservoir to establish clearance from chassis once they’re installed.
Support the frame and the axle with jack stands and remove the nuts from the U-bolts that hold the axle to the leaf springs. They are torqued exceptionally tight from the factory. We had to use “Big Wally” from Harbor Freight Tools, that heavy-duty half-inch electric impact wrench that everyone seems to have specifically for these kinds of jobs.
Once you get all the nuts off, the U-bolts pull right out. It’s all heavy-duty stuff, but it’s a really basic assembly.
Installing the lifting blocks was harder than we thought it would be. We had to use two floor jacks, one to raise and lower the axle and one to raise and lower the snout of the differential housing. Once you get it in place, the locating dowels and holes ensure everything sits where it should. This was the biggest bear of the whole installation because of how big and heavy everything was.
The three-quarter-inch lifting blocks come with new U-bolts and hardware. Start all four nuts and torque them into place using the crisscross method.
After we got everything cinched in place, we torqued the nuts to 120 foot-pounds with a torque wrench.
The factory shock mounting bolts were surprisingly tight. We had to use “Big Wally” to get them off.
Because we left the clamp a little loose, we could rotate the reservoirs away from the exhaust pipe for clearance, then tighten the clamps permanently.
The rear shocks use the factory mounting bolts. The rears are the easiest part of the job. If you don’t add the lifting blocks, the rears can be done in about 20 minutes. You wouldn’t even need to jack up the truck to do the job.
Image courtesy of Eric Green

11 COMMENTS

  1. I’m sorry…don’t rent a spring compressor to do it yourself? I stopped reading after seeing that. If you can’t use a spring compressor you should NOT be doing this job at all.

  2. How much is he towing? I’ve been towing my open trailer for years with p-rated tires and never had an issue. I towed an enclosed 24′ trailer for a while as well, never had an issue. I’m wondering how much weight you have to put on them to have a problem, and what kind of problem you encountered.

    Agreed GMC full-size springs and shocks are way too soft, I had one for a bit and it bottomed all the time.

    • He’s pulling a 24-foot enclosed now, but when he first put the LT tires on it, he also was towing a 28-foot travel trailer.

    • Remember the Ford Explorers that went “bump in the night”? They had under rated tires and all it took was a slight overload, under inflation and a hot day to make them blow. Things like rating your tires should have an eye on the maximum weight they will be loaded with, the highest temperatures they will be operated under. Pressures of course are an important issue. Definitely do not go by the max pressure displayed on the tire sidewalls like the kid at the Firestone store told me to use instead of looking up the correct setting (on the driver’s door jamb).
      Jean Genibrel
      Appliedspeed.com

  3. Why do you want to raise the rear for towing? I currently use a 2016 GMC Sierra 1500 (former U-haul truck) which I use to tow my Cayman on a Trailex CT-7541 trailer. It tows great (everything stock including P metric tires) although I agree it is harsh over bumps. Interested in the suspension upgrade, just not sure why you would want to raise the rear? I got a tow bar with approx a 3″ rise and that let’s my trailer ride level.

    Getting the proper tow bar seems alot easier than installing lifting blocks. Please explain.

  4. I put helper springs (half length springs) on my 2000 explorer (and my 89 e150 van when I had it) to assist in towing rather than lifting it. That made the world of difference when towing.

  5. The owner wanted a slight lift in the front because he uses fire roads when mountain biking, but he didn’t want to be level because he didn’t want headlights in the air when towing. The raising the rear was cheap and relatively easy.

  6. I’ve installed Bilstein 5100 series shocks on several trucks over the years. The latest (2014 F150 6.2L) just got the 5100 setup with leveling “kit” option on the front. I also went with Hellwig sway bars. This setup made some great handling improvements in the truck. Remember that going to wider wheels and tires if done correctly also improves towing stability (if done correctly).

  7. Towing technology is not a very interesting to racers and hot rodders. There are better things to think about like engines and race tires, but the fact remains that there are more people injured, or worse, from towing race cars than from racing them. The primary factors to this problem are tires, on the tow vehicle and the trailer, and with single axle trailers the tongue weight. Tires can be overloaded and/or suffer from improper inflation. (Remember the Ford Explorers with the Firestone tires.) The tongue weight on a single axle trailer should be around 10 percent of the total weight of the car and trailer. The distance from the trailer axle to the tow hitch controls this value as well as the distribution of the load on the front and rear wheels of the race car. Steve Smith Autosports used to publish a book titled “Trailers-How to tow & Maintain” by M.M. Smith. Not sure if it is still available.
    Jean Genibrel
    Appliedspeed.com

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