The new JL Wrangler Rubicon is one of the strongest off-road performers and deserves a hard look underneath to see how it does what it does. There are plenty of interesting details to eyeball – some that debuted in the JL and others that have always been part of the Wrangler recipe.
What’s more, the 2020 Jeep Wrangler Unlimited now offers a 3.0-liter turbo diesel engine that’s worth considering if extended off-road exploration is your plan. It makes substantially more torque than the 3.6-liter gasoline V6, its EPA combined rating of 25 mpg is 5 mpg better, and it can deliver something like 100 extra miles of range to wander on the range.
Does it have any downsides off road? We’ll look at that when I pull the wheels off and start poking around underneath this 2020 Jeep Wrangler Unlimited Rubicon EcoDiesel. But this isn’t just about the diesel-powered Wrangler. Almost all of the following applies to any of them.
As ever, the JL Jeep Wrangler rides on a solid front axle that delivers what hardcore off-roaders want: strength and crazy articulation. That axle is located by four control arms and a Panhard bar. I prefer to call anything with just two attachment points a link, but I’m swimming upstream in this case. Control Arm is deeply ingrained in the Jeep world. It’s best to go along.
There are two control arms per side. The lower one (green arrow) is obvious, but the upper one (yellow) is harder to see because it runs just behind the frame rail. You can see its rear attachment point if you peek inside that big hole. That odd T-shaped piece is a handle that allowed the assemblers to both fish the nut into place and keep it from spinning when the control arm bolt was torqued from the other side.
The lower control arm (green) extends forward to a bracket that’s welded to the axle tube itself. Here we can see a bit more of the upper arm (yellow), but it’s still mostly hidden.
Rubicons come with special off-road-tuned monotube shocks that are red, and they do a great job of smoothing out a lot of the lumps and bumps that you encounter when trying to make time on a dirt road. The shock’s bottom end mounts to another bracket welded to the axle tube, while the spring sits on a platform welded atop the axle housing. A polyurethane bump stop lives within the coils and bottoms against a raised area that also keeps the coil spring centered.
The upper end of the shock bolts to a massive bracket that juts up from the frame, the edge of which is used to route the front axle breather tube (white) up high where it won’t ingest water when fording streams. Axle breathers are necessary to prevent axle seals from blowing out when the differential gets hot and the air and oil inside expands. The Wrangler is rated to ford 30 inches of water, and the front axle breather’s vent is safely higher than that.
Here it is, the missing link (yellow) aka the upper control arm we’ve been unable to see. The bolted end we couldn’t see earlier remains hidden behind a shield that protects its rubber pivot bushing from exhaust heat. The front end bolts to an extension that’s part of the axle’s differential casting.
From this view, the front stabilizer bar (yellow) and the stabilizer bar link (green) look pretty typical. Serious ‘wheelers sometimes fit manually disconnectable links (one on each side) to improve off-road articulation. It works great, but it’s vitally important to remember to reconnect them when you get back to pavement. A disconnected front bar is a recipe for severe oversteer when cornering on asphalt, particularly in a sudden evasive maneuver.
But this is a Rubicon. Such disconnectable links are not necessary here because it has a factory system that can be controlled from inside the cab.
This electro-mechanical stabilizer bar disconnect system (green) is one of the Rubicon’s key features. It disconnects the bar in the middle at the push of a button if you are in 4-Hi or 4-Lo and your speed is below 19 mph. The bar will automatically reconnect if your speed exceeds that threshold, then automatically disengage again when you slow down again.
The stabilizer bar is really made of two parts that butt up against each other inside the housing, each with large teeth around their ends. A wide collar with matching internal teeth connects the two to make the bar act as one to control roll in the normal state. When you push the “Sway Bar” disconnect button the actuator pushes the collar aside so it no longer engages one half. That breaks the connection so the stabilizer bar no longer functions, at which point the Rubicon’s suspension articulation improves from merely great to truly incredible.
The JL’s front steering knuckle is made of aluminum, which is a step up from the cast iron used on the JK generation Jeep (2007-2018) that came before. Conventional u-joints are fine in this application because this is a part-time 4x4 system only meant to be used on loose surfaces. In such circumstances it doesn’t matter that u-joints produce a wavering output speed fluctuation that increases the more the steering is turned. Anything meant to drive the front wheels all the time needs a constant velocity (CV) joint.
The Wrangler uses recirculating ball steering that delivers its output through a Pitman arm (green). Its motion is transferred to the right-front wheel via the drag link (yellow), which in turn sends it back to the left front wheel through the tie rod (red). Pretty standard stuff.
The position of the JL Wrangler’s steering stabilizer (white) differs from the JK. Here the inboard end is attached to the axle tube, while the outboard end is attached to the tie rod. JK Wranglers have this the other way around.
Unlike the F-250 Ford Tremor we saw last week, the drag link (yellow) and tie rod (red) do not share a pivot point. It’s all to do with maximizing the turn angle to make the Jeep highly maneuverable on trails. The steering stabilizer (white) mounts to the tie rod end with a tidy bracket, but you also want to take note of the tie rod’s pronounced bend.
The bend is necessary to let the tire turn as far as it possibly can. It’s not quite as close to the wheel weight as it appears – there’s about a half-inch there – but I’m sure you can appreciate the importance of getting good tire size and wheel offset advice if you deviate from the standard fitment.
It takes five links to locate an axle, and this Panhard bar is the fifth one that keeps everything from shifting side to side. The right end is fixed to the frame on the driver side, while the left end is bolted to the axle.
This Front Axle Disconnect (FAD) is new to the JL Wrangler. The JK never had one. The Toyota 4Runner and Tacoma has had something similar for years, but their Automatic Disconnecting Differential (ADD) system is built into the differential housing because they have independent front suspension. But the effect is the same, and this is easier to see.
Your tires are always turning whether you are in 4x4 mode or not, but you don’t want them to back-drive the front driveshaft and the ring and pinion because the inertia and friction involved wastes gas. Manual locking hubs work great, but they’re a pain. Auto locking hubs have their own problems.
This operates much like the stabilizer bar disconnect we saw earlier. The right-hand axle is cut into two segments, and there’s a sliding collar that connects them in 4x4 mode and disconnects them in 4x2 mode. In 4x2 mode the right tire turns the rightmost axle segment, but nothing more. Meanwhile the left tire turns its intact left axle and the differential spider gears, but it can’t drive the ring and pinion or the front driveshaft because the axle segment that comes out this side of the differential isn’t connected to the right-hand tire and offers no resistance.
Trust me, it works.
The JL’s front brakes consist of good-sized ventilated rotors and a twin-piston sliding caliper.
It’s a lot easier to see what’s going on with the rear because it’s all easier to see. Notably, the shock absorbers angle steeply back, which in a textbook isn’t ideal because the ends of the frame are simply not as rigid as the middle. It would be better if they angled the other way, but you can’t do that here because of the location of the seats.
The rear end’s upper and lower arms are much easier to see. No arrows required.
As we saw up front, the fifth link is a Panhard bar. The frame end is on the passenger (right) side this time, and the axle end is on the driver side.
Another axle, another breather tube. This one terminates under the body where we can easily see it. I measured it at almost exactly 30 inches above the pavement, which means this is at the maximum fording depth of the JL. The Mojave River water crossing on the famous Mojave Road is often deeper than that, so if this were mine I might investigate ways to extend and raise this a bit.
The coil spring mounts just inside the frame, and the urethane bump stop is positioned exactly under the frame rail. You can see how it's hollow and has a bellows shape that allows it to compress gradually over a distance for a softer landing.
The rear stabilizer bar (yellow) does not disconnect, but that’s OK because it’s rather skinny. You can also see witness marks on the bump stop landing pad (white).
The diesel exhaust fluid (DEF) tank (green) is of course unique to the optional diesel engine. It’s protected by a stout crossmember and a skidplate. Both it and the exhaust pipe (white) that juts from the muffler are well up and above the imaginary line that defines the departure angle (yellow).
Another view of both the DEF tank (green) and the muffler (white). None of this would be here in a gasoline-powered Wrangler, but you would see a much more massive muffler.
The rear brake consists of a solid disc and a single-piston floating caliper, but the rotor’s hat section (green) indicates a drum parking brake.
This pull-style cable actuator confirms it. Drum brakes are self-energizing, which means the weight of the vehicle will pull one of the shoes into the drum like a wedge. You want something like that in a vehicle that might be parked on a steep slope.
And finally, these BFGoodrich wheel and tire assemblies are not light at 73.5 pounds. The BFG Goodrich All Terrain T/A K02 in size LT285/75R17 is a lot of tire, but I hear the same-sized Falkens on the Gladiator Rubicon weigh even more. Yikes.
Contributing writer Dan Edmunds is a veteran automotive engineer and journalist. He worked as a vehicle development engineer for Toyota and Hyundai with an emphasis on chassis tuning, and was the director of vehicle testing at Edmunds.com (no relation) for 14 years.
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