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Infiltrating Area BP-51: Installing Old Man Emu’s 4-Inch Wrangler JK Kit And New Bypass Shocks

Posted in How To: Suspension Brakes on May 10, 2017
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Off-road shock technology has been steadily progressing over the past decade, with a strong influence from motorsports. Bypass shocks were once only seen on Trophy Trucks, Ultra4 cars, or high-end sand cars. These days, just about every off-road shock manufacturer has a reservoir-style shock in their product lineup. Now, it’s ARB’s turn, with its suspension arm of the company known as Old Man Emu (OME), taking bypass shock technology to the next level, with the new BP-51 bypass shock absorber.

OME’s suspension engineers sweated the details and dug deep into their skunkworks department to develop a bypass shock that would offer exceptional comfort and control, on- and off-highway. BP stands for bypass, and 51 is the diameter bore in millimeters. Many bypass shocks only offer an adjustment for compression, but the BP-51 also allows for rebound adjustment. The BP-51 shocks can be fine-tuned independently with an adjustment tool, depending on vehicle weight and terrain. Currently, BP-51 shocks are available for the ’07-current Jeep Wrangler JK, Toyota FJ Cruiser, and 200-series Land Cruisers, with other models in the works.

The key element of the new BP-51 shocks is the adjustability of the rebound and compression. Depending on whether you are daily driving or heading out to your favorite camp spot with a full load of gear, the BP-51 can be fine-tuned for any situation. When your rig is loaded to the gills on a five-day trip and you hit an unexpected G-out at 60 mph, the BP-51 is designed to reduce hard impacts with the factory bumpstops as the shock reaches full compression and offers up a calm and collected ride over rough terrain. While on the highway, you can set up the BP-51 to soak up expansion joints and potholes.

The crew at Trail Tested Manufacturing in Atascadero, California, installed a set of OME BP-51s on a ’12 Jeep Wrangler Unlimited Rubicon with 63,000 miles and completely overhauled the suspension from scratch with OME’s complete 4-inch system. Specifically, on the Jeep Wrangler JK, the BP-51 were designed around a 4-inch suspension height, so anything less and you won’t receive the same results. Rounding out the package, Trail Tested also installed OME’s new adjustable upper and lower control arms, with Max-C Dual Durometer bushings. With adjustable control arms, you can customize your steering caster and pinion angles to your liking. The Max-C bushings eliminate premature bushing failure and offer a more linear spring rate while flexing out the suspension.

The 4-inch OME lift allowed us to bump up our tire size to a 37-inch diameter tire. So, we mounted up a set of Nitto’s new 37x12.50R17 Ridge Grapplers and headed east to the 2017 Easter Jeep Safari.

After removing the old shocks, coil springs, and control arms, we started with a clean slate by installing OME’s “trim packers,” which help level the vehicle and help with any sag from heavy accessories such as bumpers and winches.
Here you can see the driver-side front coil springs, bumpstop spacers, and shocks ready to be bolted up. We initially installed the OME Nitrocharger Sport shocks that are included with the 4-inch Complete JK Suspension Kit and tested them on dirt and highway for a few days to get a good baseline against the BP-51s. We drove the Nitrochargers on varied terrain and they contributed to a very comfortable and composed ride.
The BP-51, seen here next to a Nitrocharger Sport, is beefy, allowing for more oil flow and adjustability. All BP-51 shocks are manufactured in-house by ARB in Australia. The shock body is crafted from aircraft-grade (6061) aluminum, which helps dissipate heat quicker than other metals and provides corrosion resistance.
The new 4-inch rear coil springs dropped in with the help of a ratchet strap. We also ran the trim packers at every corner due to our heavier bumpers, 10-gallon accessory fuel tank, and fullsize 37-inch spare tire.
OME provides a rear track bar relocation bracket, which corrects the rear suspension roll center height and vastly improves road handling. Without it, things could get a little wonky! The OE rear track bar is utilized and the new bracket clears the BP-51 reservoirs with ease.
The new Jeep JK adjustable upper and lower control arms, with Max-C Dual Durometer bushings, are stout and made from 2-inch, 0.188-inch-wall DOM steel tube. All of OME’s control arms are shot peened, zinc electroplated, and powdercoated. The adjustable arms allow custom steering caster and specific pinion angles to guarantee a comfortable ride on- and off-road.
The BP-51s fit in the factory shock position. But where the shock bolts up to the axle, OME includes a shock relocation bracket, which moves the bottom of the shock outwards, to allow the shock body to move without rubbing against the chassis when flexing out the suspension.
Up front, the BP-51s’ reservoirs fits nicely along the frame and out of harm’s way. The front inner fender well plastic requires a slight trim to bolt up the reservoir mount, which cradles the reservoir to the framerail.
The rear BP-51s also bolt up to the stock location and easily clear the track bar bracket at full suspension travel. The rear shocks also offer a replaceable shaft guard, preventing damage to the shock absorber shaft from sand and rocks that are kicked up by the front tires.
The BP-51 is easily adjusted with this handy adjustment tool, allowing you to fine tune your rig’s ride for any terrain. For example, on our 900-mile trip to Moab, we maxed out the compression setting to help slow the sway from the 50 mph crosswinds we experienced in southern Utah. Then, when we hit the dirt in Moab, we turned down the compression a few clicks and upped the rebound to slow the abrupt side-to-side body jolts while flexing out the suspension.
Thanks to the increase in vehicle height, we were able to mount up a set of 37x12.50R17 Nitto Ridge Grappler tires. We then drove 1,800 miles roundtrip to the 2017 Easter Jeep Safari to give them a full workout. The Ridge Grapplers are a perfect blend of all-terrain and mud-terrain and performed flawlessly, delivering a quiet highway ride while offering up a ton of traction on Moab’s red rocks. The Ridge Grapplers stuck to the trail and we rarely had to use our lockers throughout the entire week of EJS.

Amazon Affiliate links are our attempt to show you real-world pricing and availability for the products we review and install, and while the Amazon links are separate from editorial and advertising, the Four Wheeler Network may receive a commission on purchases made through our posts.


Nitto Tire
Cypress, CA 90630
Old Man Emu by ARB
Trail Tested Manufacturing

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