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Build Your Jeep For Rocks: Granite-Getter!

Posted in Project Vehicles on June 1, 2011
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You can plow through mud. You can blast over sand. You can bash through snow. But you gotta tiptoe over rocks. Let’s face itrock is the one obstacle you’ll encounter that’ll beat you 9 times out of 10. Wood may splinter and ice may shatter, but rock will dent, rip, tear, and make a mess of most components on your Jeep. If you’re heading in the rocks, you’ll want to up-armor the underside of your Jeep for survivability.

In addition to bash-proofing your Jeep, keep in mind that negotiating rocky trails takes a high degree of finesse. Throttle manipulation, tire placement, and steering all converge into one fluid ballet on wheels. Screw it up and you could be looking at a rollover, shredded tire, busted drivetrain parts, or munched sheetmetal. Likewise, your overall vehicle build needs to have a high degree of balance. Tires and wheels that are too big and heavy can overwhelm axleshafts and steering components. Too much armor/weight can overburden your clutch. Too much axle can leave you high-centered. Too much gearing will leave you with no wheel speed. And not enough gearing can leave you making up new and exciting words your kids shouldn’t repeat at school. So if you and your Jeep are rock-bound, check out these pre-trip prep tips that will bolster survivability.

Cage & Safety
Putting your Jeep into off-camber situations increases the likelihood of a rollover. Depending on the trail, that could mean anything from a simple flop on your side to barrel-rolling down a 200-foot cliff. A good roll cage with solid construction should be high on your list. One that’s tied solidly to the frame is ideal, but one with large floor plates that won’t punch through the tub floor is better than nothing. Also, a good three-point seatbelt or four- or five-point harness is preferable to a simple lap belt, but a lap belt is preferable to nothing at all. Always buckle up.

Big tires exert big stresses on your steering box and linkages. But even if your tires aren’t huge, running rocks still works your steering components hard. Full-blown hydro-assist setups with a high-performance box and pump are great, but aren’t for every budget. If you can’t afford the bling, plumb a transmission oil cooler in-line into the low-pressure return line between the box and pump to prevent boiled fluid at low speeds. Check your box mount and add a brace if necessary, and upgrade your tie rod and drag link to heavy-duty, bend-proof stuff. Tubing with a wall-thickness of at least 0.120-wall is mandatory. Finally, if you’re using tie rod ends, go large and chuck a spare or two in your toolbox. Rod ends should have double-sheer mounts so that the bolt holes don’t get wallowed and sloppy.

Body Armor
One of the first mods you should make before venturing in rocks is a good rocker armor system—whether steel or aluminum plate or tubular style. Rocker armor with tubes that extend out past the body line can help keep the tub/body away from trail obstacles. Also, rear corner armor in both steel and aluminum is available nowadays for most Jeep models, including Cherokees. Front tube fenders offer more crunch-proofing than simple sheetmetal, and as always, a good set of heavy front and rear bumpers can help protect sheetmetal.

With lockers comes finesse. You’ll be able to traverse the trail in a smoother, more controlled manner with front and rear lockers than if you’re running limited slips or open diffs. Additionally, a full-case locker will usually be a lot stronger than a lunchbox-type locker inside a factory carrier. Don’t be afraid to use a spool out back if you’re building a short-wheelbase Jeep that sees street driving. The auto-versus-manual locker question can be a matter of personal debate, but there’s no arguing the efficacy of a locker in the rocks.

Undercarriage Armor
Rocks can spin, flip, flop, and plain reach out and grab vital undercarriage components—even when you think you’ve cleared them. Protect your engine and transmission with armor. Oil pan armor is available for a large number of 4.0L-, 2.5L-, and 3.8L-equipped Jeeps. Also, protect the T-case, steering box, and fuel tank. If your muffler is vulnerable, ditch the stock-type muffler for a fully welded variety. As for material, steel will be the most durable, but you can find aluminum or even UHMW Polyethylene (cutting board material) armor that is much lighter than steel. Aluminum may stick to rocks more than steel or UHMW, but its low weight and relative low cost makes it a good option.

Low-range axle and T-case gearing will make your Jeep easier to maneuver in the rocks, take strain off your transmission and/or clutch, and improve throttle finesse in a carbureted application. The downside is going too deep with your gearing and limiting your wheelspeed. Sometimes you want to blip the throttle and spin the tires to get up and over a hard obstacle. For your T-case, multi-range gearboxes that offer more than one low gear ratio will work best in most scenarios. Shoot for a crawl ratio of around 40-60:1 with an auto and 100-150:1 with a manual for optimal performance.

Tires & Wheels
If you haven’t bought your wheels yet, go with beadlocks. Running low tire pressures in the rocks is a must. And often, to get the most out of your tires, you’ll have to drop the pressures past the point at which bead retention is possible. Not running beadlocks throws traction out the window at the cost of gobs of off-road performance and ability. As for your tires, look for gnarly, thick sidewalls (three-ply or better) with good gash resistance and big, grabby lugs. Aggressive bias-ply mud tires are almost always good in the rocks, but most modern mud-terrain radials are able to offer a level of rock survivability once thought impossible in a radial.

Fuel Injection
Running your Jeep at all angles can be an exercise in frustration. There are a good number of off-road carbs nowadays that work well off-road. You can even make junkyard Q-Jet four-barrel and Motorcraft two-barrel carbs behave at angles, but there’s just no getting around the performance offered by fuel injection. Many Jeeps from ’87-on came with fuel injection, but even if you’re running an older factory Jeep or swapped-in engine, an ever-increasing number of aftermarket injection systems are available today that will make a night-and-day difference in your off-road drivability.

Axles & Axleshafts
Not everybody needs Rockwell or Dana 60 axles. However, if you’re hitting the trail with 37s on your Dana 27 front axle, you’re asking for trouble. Within reason, you can usually get away with upgrading your Dana 30 or Dana 44 axleshafts to good aftermarket alloy units running high-quality U-joints with full-circle clips. The full-circle clips won’t spit out like factory C-clips can, allowing the U-joint cups to walk out of their bores. Rear axles (especially two-piece shafts) also benefit from aftermarket one-piece shafts. Consider 30-spline shafts good for up to 37-inch tires (within reason). Any more than that and you should start shopping for heavy-duty aftermarket axles or 1-ton junkyard stuff.

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