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Adding Bypass Shocks to Our Solid-Axle F-150

Posted in How To: Suspension Brakes on July 24, 2019
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Over years we have upgraded our 1977 Ford F-150 with a 460 engine from LA Speed, an Offroad Design Doubler, and Super Duty axles with Detroit Locker and Sierra gears. All of that combined to make a truck that was reliable on the street and capable on the trail, but limited to low-speed crawling. While we had plenty of engine to go fast, the single 2-inch shock at each corner took issue with having to control the 6,900-pound truck during spirited driving off-road. To resolve this issue, we installed some used 3-inch bypass shocks that we were able to pick up at a fraction of their retail price.

We should note that this is not the correct sequence of events if you want to maximize wheel travel. The right thing to do would be to remove the front coil springs, determine how much uptravel you have before suspension components start crashing into each other, and measure how much droop you have before the driveline or suspension binds. Similarly, in the rear you would remove all but the main leaf of the springs and cycle the suspension to full bump and full droop. The next step would be to order shocks of the appropriate length. That is expensive though.

Instead we took the 10-inch-travel bypass shocks we purchased used to Rock Hound Off Road in Auburn, California, and had them build custom mounts front and rear. Rock Hound set up the shocks in the middle of the travel to utilize the bypass tubes as the suspension cycles. They then built bumpstop mounts to prevent the shocks from bottoming and added limit straps to keep the shocks from over extending. While we left some suspension travel on the table by approaching things this way, the price made it worthwhile. And with 42-inch tires, low gears, and Detroit Lockers, we don't have to worry too much about articulation to get through most trails.

So why go through all the trouble? The larger-diameter shocks allow for a larger piston and shims, which provide more precise velocity-dependent valving. They also hold a larger volume of shock oil to prevent fading during continued use, and they are completely rebuildable and customizable. The bypass tubes allow for further customization by making the shock valving position-dependent in addition to being velocity-dependent. As the name suggests, these tubes allow oil to bypass the shock piston in a certain zone of the shock.

Of course, all of this adjustment means that there's just as much potential to get things wrong as right. Our used front shocks came off of a sand truck with a small-block engine and leaf springs, and our rear shocks were for a Ford Raptor, so both ends needed to be revalved and fine-tuned for our heavy Ford. Samco Fabrication has years of experience tuning the suspension on championship-winning desert race trucks, including stock class vehicles that have the same limited amount of suspension travel as our Ford. After riding in our truck over a test loop, Samco was able to adjust the compression and rebound tubes on our shocks to make it ride smoothly over washboard while still withstanding larger hits without bottoming out.

Considering that we did not change our radius arms, coil springs, or rear leaf springs, the improvement in ride quality that was achieved just through the use of new shocks was astonishing. The truck rides better on the street now with more rebound damping to control the heavy engine, 16,500-pound winch, and pipe bumper hanging off the front end. In rockcrawling the difference is negligible, but as speeds increase on the trail so does the difference in performance, making our old Ford a well-rounded vehicle for nearly any terrain.

No going back now! We started by removing the Super Duty shock towers, but we retained the original coil buckets on the frame. The larger shocks needed stronger mounts that could accommodate the physically larger shock body and provide space for the bypass tubes.
Note the orientation of the tubes on the Fox bypass shocks, and the blue, red, and gold anodized fittings on the end of the tubes. The blue bypass adjuster controls compression and the red one controls rebound. The gold adjuster is a Fox-specific piece that allows the oil to flow both directions, controlling both rebound and compression. This adjuster is typically run in the middle bypass tube to adjust the ride where the shock spends most of its time.
This would be over $4,000 in shocks sitting on the tailgate if we bought them new. We spent $1,500 on used shocks, which still ain't cheap, but it definitely beats paying retail. The annual Curt LeDuc Swap Meet, which is held in Southern California each February, is a great place to find deals on used race parts.
After measuring our shocks' collapsed and extended lengths, Chris Sparks from Rock Hound Off Road started taking measurements in the wheelwell to determine where to position the shock mounts. He set the shocks up in the middle of their 10-inch travel at ride height.
Sparks made us shock hoops out of beefy 1.75x0.250-wall DOM tubing that were welded to the Ford's frame. The hoops fit just under the inner fenders to position the shocks up as high as possible.
The uptravel in our front suspension was limited by the track bar contacting the tie rod and the coil springs going into coil bind, where each individual coil is touching the adjacent coils. Rock Hound set up the bumpstops to prevent both of these conditions from occurring.
Mounting the shocks farther up the radius arm would effectively give us more travel at the wheels, but 42-inch tires need a lot of real estate when you have them turned to full lock. Rock Hound mocked up the shocks and cycled the steering and suspension before burning anything together. They ended up positioning the bypass tubes to the inside for added clearance.
The lower shock mounts were moved from the lower bar of the radius arm to the upper tube. The tabs had to be long enough to allow for articulation since the track bar causes the axle to move side-to-side. Longer tabs are weaker though and minimize tire clearance, so packaging everything in the front end was a balancing act.
We added limit straps from WFO Concepts to prevent damaging the shocks at full extension, particularly given the unsprung weight of our Ford. WFO Concepts limit straps are available in a variety of lengths and are made in the USA from quad-wrapped 7,000-pound webbing to minimize stretching.
We like the compliance of foam bumpstops over polyurethane for applications like this. We found these inexpensive Crown Automotive bumps on Summit Racing Equipment's website. We just searched for bumpstops and then specified foam and searched through the results until we found something that would work.
The rear shock mounts were inboarded on top to allow a long-travel shock to fit without the need to cut through the bed. This is pretty common on rockcrawlers, but bypass shocks need to be mounted upright and cycle through the entire travel in order for the bypass tubes to function properly.
Cutting holes in the bed of our truck was the most nerve-wracking part of the entire process. The leaf springs on our Ford are outboard of the frame, which complicated the packaging of the shocks. Rock Hound ended up mounting the shocks on top of the leaf springs and through the bed just inside the wheelwells.
The rear suspension was much easier to install than the front suspension since there were no concerns about steering or a track bar that moved the axle from side to side as it cycled. The leaf springs do effectively grow and shrink in length though as the suspension cycles and the shackle moves, so that must be taken into consideration.
While we were timid about mounting the shocks through the bed, Rock Hound did an excellent job packaging the 3-inch King bypass shocks on each side of our spare tire where they are protected and take up minimal bed space.
The last, and arguably most important, step is to tune the shocks for your specific application. Samco Fabrication has years of experience tuning desert race trucks, and it was able to use our feedback regarding the truck's ride to make changes to the shock damping to achieve the performance we were after.
After tuning the shocks, we spent the weekend camping and driving backroads. The improvement was more noticeable as speeds increased, particularly with regard to the rebound. We put zip ties on the shock shafts to determine how much of the travel we were using and never bottomed out. We will have to try harder next time!

Sources

Crown Automotive
781-826-6200
http://www.crownautoparts.com
Fox
800-369-7469
http://www.ridefox.com
King Shocks
Garden Grove, CA
714-530-8701
http://www.kingshocks.com
Samco Fabrication
775-856-4100
http://www.samcofabrication.com
Summit Racing
Akron, OH
800-230-3030
http://www.summitracing.com
WFO Concepts
Auburn, CA
530-268-9494
http://www.wfoconcepts.com

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