Gourmet Jeeping

I use the old fashioned term "jeep", and "jeeping" with a lower case "j" to denote a generic four wheel drive sport utility vehicle, and the use of same. Long before Chrysler bought out AMC, I was jeeping. I have owned and driven the wheels off of 4 Jeeps (upper case "J"), along with 2 Landcruisers, and a Scout Diesel. So all of you Ford, GM, and Chrysler fans out there, this is not about moniker, it's about components.

Hard-core rock crawling requires more actual technique and finesse from the driver than any other style of slow 4-wheeling. Mongo high-end horse power, chrome diff covers, lift blocks, and giant tires are not the ticket. The preparation of the jeep is important, but the elegant style of the driver is more important. It's the equivalent of "trials" for BMX and mountain bikers. The overall need for the machine is balance, and for operator is elegance. Building a rock crawling 4X4 may or may not strike a balance with street operation. There are usually center of gravity, gear ratio, and handling irregularities that must be traded off. Having 25" of clearance under your rocker panels may preclude the vehicle's use in taking your wife to the Philharmonic.

Consider a few basics. The longer your wheel base is, the more vertical clearance you need. Gears that seem way too low on the street are woefully too high (tall) for hard core rock crawling. The lower your crawl ratio is, the more heavy duty your drive train must be to compensate for the added torque on the components. It's all part of a mechanical chain, so we look for the weak link. The more torque and horsepower your engine has, the more heavy duty every other drivetrain part must be. If you have a short temper, or are soaked in testosterone, take that into consideration. Some need to be more mellow and patient, and others need to be more aggressive and less apprehensive. We're all in there somewhere, and there's a good balance in there somewhere.

Heavy duty? The weak links in vehicles used in rock crawling usually are most apparent during extreme use; when you are really pushing to the max.. Each make, model, year, and components of stock jeeps have strong and weak points. The smart rock crawler swaps weak components for stronger ones. In fact, rock crawlers typically modify and change more mechanical components than any other jeepers. When was the last time you heard a jeeper say, "It's too heavy duty"?. Your job in preparation is to eliminate parts that might break on the trail, remembering that overkill on one component may endanger another now comparatively weaker one.

Below is an incomplete list of some desirable elements for jeep and jeeper:

1. Gearing: A very low, low gear is probably the most important mechanical requirement for rock crawling. Their is no substitute for gear reduction. Without the lowest of lows, the greatest clutch in the world will smoke on the "Sledgehammer". A low range, low gear ratio (called the crawl ratio) from 45:1 down to a ratio of 60:1 or even 100:1 is desirable. To help get you there, some numbers that come to mind are: 33", 34", and 35" tires; Dana 44, 60, and Ford 9 inch differentials; Dana 20, 300, and Spicer 18 transfer cases; 4.11, 4.56, and 5.38 axle gearing; Borg Warner T-18a and T-19; SM420, NP435, NV4500, TH400, TH700R4, and 4L60 transmissions. Be wary of cases of aluminum. Just the overall ratio in low range, low gear is not the total answer, however. I have seen flat head 4-bangers out crawl big V-8's, because they have the torque where they need it, but not so much as to loose traction. More about that below.
2. Very high ground clearance. There is virtually no stock vehicle that has enough. Rock crawlers spend time lifting their jeeps and eliminating things hanging down that can impede their progress and get scrapped or ground off by the procession of slowly moving rocks passing beneath. This not only includes things under the jeep, but things fore and aft, and to each side. My brother John went so far as to cut the bottom 4" of sheet metal off all around his early Bronco and replaced things like the rocker panels with unobtrusive thick wall steel tubing. As expected, his first trip through the "Sledgehammer" pretty much destroyed the original rocker panels. His "Panels of Steel" gives new meaning to the term "sled". He maximized his ramp approach, ramp breakover, and ramp departure angles. The problem is in real life, there is no ramp, only a crude and undulating surface. The balance here is only lifting what you need- not too much, but enough. Consider your drive shaft angles. Over lifting causes terrific strain on your drivelines. Consider using CV U-joints, instead of factory single cardans.
3. Engine: Torque is king. Gobs of torque below 1500RPM is a must. A mild bump stick and a heavy flywheel are desirable. Many main bearings are good. A long stroke is good. It just doesn't matter how many cylinders you have when you are moving at less than 1 MPH. We're talking about a power plant at the lower end of evolutionary scale. It matters how much twisting power you can reliably supply to your super low gears below a 1000 RPM. It matters that your carburetor can smoothly operate at 400 RPM, on a 45 degree angle, up or down hill, while pitching wildly from side to side, and keep the rig moving. It doesn't matter what the name says on the engine, only how it behaves in the lowest 10% of its RPM. Some of the most enjoyable, and most unlikely rock crawling I ever had was with my old 118" wheel base Scout Traveler with the factory 6-cylinder Nissan Turbo Diesel, springs-over-axle, the Borg-Warner T-19, Dana 300, 3.73's, and 33-12.50 Muds. It sure didn't look like much on paper. The engine weighed in at almost 900 lbs, put out only 101HP, but with the help of fuel injection, 23:1 compression, trac-locs, and a heavy flywheel, it was primordial ooze in the flesh. It was a slow, smoke belching pariah on the highway, but turned into Tyrannosaurus Rex in the rough. It was very difficult to spin a tire. You might consider fuel injection for rock crawling. It operates consistently at any altitude and any attitude. I guess the down sides are high cost, more complicated, and what to do when it stops working, a days drive from anywhere. Unless you tow your jeep, the compromise is a power plant that will get you to the trailhead with a modicum of style. Running 5:38's on the highway at 4200 RPM is not my idea of a quiet drive to the country. What about overdrive then? I don't recommend it. Not for rock crawling. I had a couple of overdrives on my jeeps, and always had trouble with the planetary gears, too complicated for that much torque. Keep it simple, keep it tough.
4. Locking differentials. For serious rock crawling there is no substitute*. Air lockers seem the most flexible, since you can turn them off, and the most expensive. Detroit lockers are bulletproof. I have Lock Rights, and I have mulched the pins on two occasions. Lockers do have a drivability factor on the street you must get used to, since you can't turn them off. On a high speed road, in a power turn, they tend to over steer; off the gas they tend to under steer. Mix these factors in a curve and you will have much adjusting to do. Differential synonyms: diff, pumpkin, pig, chunck.* [Disclaimer: An experienced driver with limited slips, can do as well on the rocks as a driver with a lower skill level and lockers. A driver with exceptional skill and talent can do as well with open differentials, lower tire pressure, and a good brake and parking brake technique, as a driver with the lower skill level and lockers. ]
5. Soft and compliant springs and shocks. You want smooth and unimpeded travel, with a large range of motion. This is especially important in off-camber situations. Do everything you can do to keep your wheels on the ground. If you have wheels off the ground, they cannot control your motion. Stiff springs arguably help in ground clearance and racing, but are the wrong choice for rock crawling. You want gravity to pull down as evenly as possible on all wheels. Detach your anti-sway bars at the trail head. We just wire ours up to the frame on our CJ8. Our shocks are rather weak compared to the prerunner style, but have a very long stroke. Sooner or later, most hard core rock crawlers with leaf springs go to springs-over-axle. Yes, your center of gravity is higher, but it's a good trade off for clearance. The other downside on S-O-A is the dreaded axle wrap. custom assembled (trying different combinations of leaves) springs will give you the balance you need. Large, high HP engines exacerbate the situation. The sound of graunching steel you hear coming through the floor of your jeep becomes less frequent. When you retain the OEM spring pack, plus some extra leaves, the ride is usually superior to aftermarket, and a lot cheaper. In fact, for many low slung jeeps, there is no finer or cheaper option than springs-over-axle. You don't see kits for this in the aftermarket catalogs, because there is hardly any hardware. It's mostly labor, but it's not bolt-on.
6. Good visibility over the hood and fenders. Top and doors off, and windshield down helps. This also helps lower your overall center of gravity. Fold or remove your mirrors before starting on the route. Some folks even re-aim their mirrors down to check side clearance.
7. Short wheel base /narrow track/ fast steering. Generally it is more important to get around very tight turns with a minimum of see-saws. Steering that seems too fast for dirt roads and freeways, has a home in rock crawling. The one admonition, however is the incredible torque put on king pin u-joints, power steering units, and the frame area where the power steering box is attached, during locked turns. Some jeep trails are a nightmare for any but the narrowest of jeeps. Don't build in trouble by having too wide a vehicle to start with.
8. Smooth and controllable clutch. If you have a large competition style clutch, the pedal effort may wear on you during hard core rock crawling. A clutch that has a nice wide "friction" area is desirable because you can control it. I've driven some heavy duty clutches that had no "friction" point at all, and were just on or off. You don't want this. Speaking of clutches. One clutch point every rock crawler faces sooner or later is the dreaded stall in exactly the wrong place- usually with a wheel hanging off the edge, or with your front end facing the sky, and your brake lights blazing weakly over several hundred feet of loose talus randomly organized at the maximum degree of repose. The usual scenario is that your brake foot is down on the pedal at 200 ft. lbs., and beginning to sewing machine up and down, because that mindless hydraulic pressure for the power brakes only works when the engine is running. Gulp! The tried and true remedy is to slide the heel of your 200 foot pound brake foot over to the gas pedal, push the clutch in, and try to restart by juggling 3 pedals with 2 feet. Control this ain't. You have other options which are used by the savvy rock crawler. If you feel that the engine is not flooded, but has just run out of twist, simply leave it in gear and turn on the starter. More often than not, you will be on your way. No matter what transmission you have, the slowest gear on the jeep is the spur gear on the starter motor. Well, O.K., your winch motor may be right in there too. More than a few times, it was prudent for me to use the starter motor to grind a few feet, in gear, away from some compromising (read heart-in-the-throat) position before I even dared to touch the clutch. If the engine is flooded, you'll have to push in the clutch. But wait... not yet. I have installed dash mounted hand throttle cables to many of my jeeps to keep the engine at a fast idle during extended winching. It also works well as an alternative gas pedal. One foot on the clutch-CHECK. One foot on the brake-CHECK. One hand on the hand throttle-CHECK. I've often thought that a better system would be a lever hinged at the bottom, with a handle, about 8" long and the throttle cable connected about 1" up from the fulcrum, with enough friction to stay where you leave it. You might have better finite control of the accelerator during former 3 pedal starts. Here's your million dollar scheme! I'll buy one.
9. Automatic transmissions have come a long way the last few years, and with a large oil cooler and aftermarket low gear, you can look as good as the best rock crawlers with a clutch. The questions are: durability, downhill braking, how short a rear drive shaft can you live with, what do you do with all of that heat, and what do you do when the engine stalls? With the time honored one foot on the gas, and one foot on the brake, you can be so smooth-so elegant. Those other folks with clutches will look like they are playing piano with boxing gloves compared to your dynamic oozings.
10. Tools enough to fix as many contingencies that you can imagine, or you have heard of going wrong on your particular jeep.
11. Keep the weight down. Take only what you need. Don't overstock. After much backpacking and mountain biking, I use the same philosophy about what to take for jeeping. Another backpacking concept is packing your gear in sacks, not boxes. This works very well for small cramped areas like the back of a CJ5. You can pack more in a given space with less rattles, and more what I call "moldability". As you repack for another days crawl, the mass tends to change and reduce. It is important to make and keep a list of what to take, and update it after every trip. Some of the best backcountry ideas are written down on the trip home.
12. Wheels, tires and pressure. Wheels for rocks should be of steel. Aluminum is lighter, cooler looking, but prone to break and crumble when abraded between a rock and a hard place. A medium wide wheel is probably the best compromise for rocks. There are many opinions about tires, so I will only give a general view. Tall is good. The jury is still out on wide. 33", 34", and 35" are the current standard rock crawling diameter. Some folks like a tall and wide tire with an aggressive tread. This is fine for brute traction, but the downsides are the high unsprung weight, a higher chance of hitting every rock on the route, and the added stress on your steering, brakes, and drivetrain. I have used 33/9.50's Muds on my CJ8, and they work very well. They are tall and skinny: not very sexy. I find it easier to pick my line, and stay out of trouble. I find the narrower a tire is, the more you must play with the pressure in the rough. Each weighs 44 lbs. Compare this to the 33/12.50 Muds that weigh 67 lbs. each. Quite a difference. If the rest of your drive train is up to it, wide tires can be used with great success. I would say the best balance is tall and medium wide. After buying and wearing out at least 30 sets of tires for jeeps, I do not say this unadvisedly.
    Tire pressure for hard core rock crawling is very subjective. It depends on the weight of the vehicle, how stiff the sidewalls are, how large the tire is and what width the wheel is. It also makes a difference if you are running radial or bias ply tires. If the rocks are very sharp, or if there is much high speed running, I will only air down to 18-20 lbs. If the rocks are more rounded, or if the terrain has more sand and duff, I air down to 15 to 18 lbs. for flotation. Sometimes, as the 100% effort, I have gone down to 10 lbs. or less. You have a high risk of tubeless tires walking right off the rims at that pressure. Tires are more vulnerable at lower pressure. Talk to people about their experience with tires. You'll find a wide variation of opinion.
    Equipment for rock crawling is in a constant state of flux and improvement. What seemed impossibly low geared just a few years ago is now the norm. 35" tires seemed way too big just a few years ago. Now they're the norm. I predict 6 wheel drive will make a comeback.

We've gone over the basics about the machine, but what about the Operator? (You just can't buy experience.)

This is a far more subjective measure than equipment. I think the most important quality of the driver is what I call smooth elegance- when he or she "becomes the trail". A fine Shakespearean actor doesn't just act, but "becomes the part". It's almost a Zen-like. You know where all of your tires are at any given moment, and you feel that you and the route and the rocks are one. This includes memorizing where you are on the trail. This takes a lot of concentration and involvement to take mental snap-shots, and then remembering that picture when you are driving over it.

You also have to keep an eye on the route farther ahead. It also involves not fighting or trying to beat the route into submission. Sometimes you need to be aggressive. But most of the time you want to flow over the terrain like water down a stream bed. Take advantage of rocks to slide sideways, always in control, and pick routes that your tires can go up and over to keep the pigs from getting gnarly. Once the wheels start to spin, forward motion is usually over. Let up on the gas, just before you stick, and see if you can finesse up and over. Turn the wheel side to side and see if you can get a fresh bite on the terra. Sometimes you know by looking, that you do need momentum. Again, use just what you need, but no more. Many times letting up on the gas will give you more traction. You are putting less torque to the wheels and they will be less likely to overcome the friction on the ground and spin the wheels.

Knowing what you and your jeep can and cannot do is a good thing. Of course if we are very aggressive, we usually find out the limits in a hurry. Try to have a detached and ego-free spirit about you and your jeep's abilities. It's just a hobby- it's just a pile of metal. Feel what the jeep feels, like it was your own body. Feel the stress on the springs, frame, and drivetrain.

Learn your craft under low stress conditions. Except for the logistical support you get by going with a large group, don't be intimidated by all the talk. Go in a small non-confrontational group, with at least one expert. Watch what that person does on the bad stuff, and try to emulate their technique. On the other hand, it is also good to watch what not to do. We can learn from watching someone else's mistakes.

Don't be in a hurry. More damage is done when drivers try to go too fast. It is important to know exactly where your pigs are, and the clearance under your axles, bumpers, skid plates, frame, and rocker panels, and that this is a situation in flux. Tires that glide silently over obstacles at 32 lbs of air, may not clear those obstacles at 18 lb.

When you come off a large rock, even at a crawl, your compliant springs may compress and rebound, putting your control at risk. Ooze rather than bash. Emulate a snail. If your gears are low enough and your engine will run smoothly at very low RPM, keep your foot off the clutch. As soon as you push the clutch in, your control diminishes.

And what do I rockcrawl in?
A '82 Jeep Scrambler (CJ8), with a stock in-line 6., Ford (Borg Warner) T-19, an all synchronized, mid ratio 4 speed (5.11:1 low) with adapters from Advanced Adapters; Dana 300 transfer case (2.61:1 low) with Currie twin sticks and power steering brace, springs over axle, 4" drop pitman arm, 35/12.50 Mud Kings on stock 8" wheels, medium shocks, Custom heavy duty drive shafts and short shackles, 6 leaf front springs, and 7 leaf rears, Dana 30 Front (stiff preloaded Trac-Loc), Jeep (AMC) Model 20 rear (Lock-Right Locker), and the tried and true Warn 8274 Winch. I tried to make every drive train part more heavy duty than the torque of the engine could break. Rocker panels to ground is 25". The crawl ratio is 48:1.
What would I change? The crawl ratio. It needs to be about 60:1, or 70:1. At one time this was my daily ride, and I chose to compromise rock crawling with the street. I used all 4 synchronized gears on the street. Now that it's used just for hard core jeeping, it is time to go to a transmission with a 6.4:1, 6.68:1, or 7.05:1 low gear. I am going to fuel injection and a heavier flywheel at overhaul time, which is imminent.