Check Tires & Wheels

• Tread Condition
  • Make sure that you have adequate tread on your tire, particularly if you will be in muddy conditions.  Remember that significant tread wear and damage can occur on the trail, so if your tire's tread is worn a bit thin it will be better to be safe that sorry and replace that rubber before you leave.
• Sidewall integrity
  • Make sure the the sidewalls of your tire are in good condition, look for cuts or chunks.
• Valve Stems
  • Your valve stems should be undamaged and not cracked.  All should have caps to prevent the internal mechanism from being damaged.  Metal caps will help prevent the stem from being crushed so you can not air up adequately after the trail.
• Inflation Pressure
  • All tires should be inflated to the same pressure on and off the street.   Uneven pressure can cause your steering to pull, poor braking and accelerate wear in the differential.
• Beads
  • Make sure that the bead is well seated on the rim and is not damaged.   Inspect to make sure that no material is caught in the bead of the tire causing small leaks - particularly when aired down.  Check the bead when you air back up when leaving the trail as well.
• Spare tire
  • Your spare tire should be in perfect condition and the same diameter as your primary tires (width can be different).  Do not take a chance on a spare that is in poor condition - it is the most often used spare part on the trail.  It should be fully inflated and have all lug nuts.
• Check wheels for cracks or damage.
  • Check your wheels for damage or corrosion. Pay particular attention to the bead area, the valve stem and the hub area.  Replace any damaged wheels.   Include your spares wheel in this check.
• Check all lug nuts & studs, carry a full set of spares.
  • Check all lug nuts and studs.  Torque all of them to the recommended specification before leaving, at the trail head and when airing back up after the trail.   It is common for lug nuts to loosen on the trail and I can tell you from personal experience that it is no fun watching one of your wheels and tires pass you at 65mph on the freeway as you drive home.  Carry a full spare set of lug nuts at all times.
• Check lug wrench.
  • Make sure you have a lug wrench, that it is the right size for your lug nuts, and that it is in good condition.  It should be readily accessible but well secured.   As a backup, make sure that your tool kit has a socket wrench or other wrench that also fits your lug nuts.

Check Suspension

• All bolts torqued correctly? Check for corrosion / mangled bolts
  • Torque all suspension bolts & nuts down to correct specifications, may of these should not be too tight or they will bind, too lose or they will fall off.   Nylock nuts or lock-tite is a good idea on critical fasteners.
• Bushing condition
  • Check all suspension bushings, replace any that are in poor condition and lubricate any that need lubrication.
• Cracks or twisted components
  • While you are under your vehicle, check all components for twisting or cracking.  Pay particular attention to spring mounts, control arm mounts, control arms, shackles, and track bar & sway bar mounts.  Correct any damage before leaving.
• Clean and lube leaf springs
  • This may seem like it's fanatical, but you will notice a big improvement in ride and performance.  Disassemble leaf spring packs, carefully clean them and smooth any roughness, lubricate them with a light film of very heavy grease and reassemble the leaf pack.  If you have leaf packs that ride at different heights (due to sag) you can mix and match leafs in opposing left/right packs (not front and rear) to help even them out a bit. [Click here for a few pictures]
• Shocks - bent, dented, leaking, interference
  • Check your shocks, bushings and mounts.  Look for dented or leaking shocks, also look for possible interference, especially at full articulation.

Chassis

• All bolts tightened to correct specs?
  • Check all chassis and frame bolts and nuts and make sure they are undamaged and are tightened correctly.
• Cracks, rust, corrosion
  • Check the frame for cracks, twists, rust & corrosion.  Correct any damage before leaving.
• Body mounts & bushings
  • On body on frame vehicles, check all body mounts and bushings.   Replace any damaged or cracked ones and make sure they are all tightened correctly.
• Skid plate & mounts
  • Check the skid plate(s) and all mounts (including transmission & transfer case mounts).  Tighten any loose bolts.  Correct any interference between the skid plate and any component (such as a driveshaft).  Reinforce any potential weak spots.
• Interference
  • Check all components for possible interference, particularly during maximum articulation and/or at full steering lock.  Sometimes, due to vehicle modifications or "trail tweaking" new problems can develop that were not there previously, correct any possible problems.
• Lubricate all points.
  • Lubricate all standard & supplemental chassis lubrication points.

Brakes

• Check pads & shoes
  • Make sure that you have adequate braking material, in good condition and without contamination (such as grease or oil).  This is your life, don't take chances on borderline OK, replace anything that is questionable.
• Check rotors & drums
  • Check brake drums and rotors for damage, scoring and minimum thickness (usually stamped on the component).  Again, correct any problems before you leave.
• Check and/or replace fluid
  • Check brake fluid, add as necessary and replace old or contaminated fluid completely.  If you run your brakes hot, it is a good idea to do replace the fluid anyway.
• Bleed brake lines
  • Bleed all brake lines.  Check bleed screws for leaks and general condition - clean and cap if possible.
• Check for interference or adequate line length during articulation
  • Check your brake lines to may sure they are long enough and do not catch on anything when full articulated and at full steering lock.
• Check lines for cracks, cuts, abrasions, etc.
  • Check all brake lines for cuts, abrasions, cracks, poor fittings, leaks or any other possible damage.  If you find a problem - fix it!
• All fittings tight?
  • Check all fittings, mounts and bolts for tightness.  Make sure you carry the right tools to service your brakes!
• Adjust E- brake
  • Adjust your emergency (parking) brake so that it holds your vehicle securely but does not drag.  Replace any damaged component in your E-brake system.   Don't have an emergency brake? - Get something (like a line lock) and install it!
• Brake lights
  • Check and make sure that your brake lights function correctly - replace any burned out bulbs or damaged lenses.  Since tail light damage is common on the trail, it would not be a bad idea to carry a spare bulb and some tail light repair tape to avoid a fix-it ticket on the way home.

Axles & Differentials

• Check hubs and seals
  • Check for damage or leaks - correct any problems.
• Open each differential, inspect gears and teeth conditions, check for chunks of metal, change oil.
  • A metallic powder in the bottom of the case is fairly normal, big chucks of metal are not.  Check the condition of the gear teeth on the ring and pinion and in the spider gears.  If you have never seen the inside of a differential before then by all means take a few minutes and see how it works - someday you may have to fix something in the field.  Change the gear oil, it is always a good idea to use a synthetic oil.  If you have a limited slip differential make sure that you use the correct oil or add a limited slip additive.
• With ARB air lockers check air lines, condition, fittings, clearances.
  • If you have ARB,s check all of your air lines and fittings and make sure that the air lines have adequate length during full suspension travel and do not catch on any component.  It is always a good idea to carry spare air line and a repair fitting.
• Check vacuum lines and shift motors on central disconnecting axles.
  • If your 4x4 has a vacuum actuated front axle disconnect, check the vacuum lines and make sure the shift motor is operating correctly and is not damaged.
• Eyeball axle housing for cracks, straightness, damage, rust corrosion, etc.
• Check vent lines.
• Check pinion for play.
  • For both the front and rear axle check the input pinion for play which may indicated a worn bearing.
• Check front U joints - make sure you have a spare!
  • Check the U-joints in your front end knuckles (and the rest of your driveline).  Lubricate them and make sure you carry at least one spare of every U-joint on your 4x4.  These are another commonly used spare item on the trail.   Make sure you know how to change them and that you have the tools to do it.
• Check front knuckles.
  • On your front axle check the steering knuckles, ball joints, steering arms, etc.  Fix or replace any damage or worn components.

Driveshafts

• Check U-joints & lubricate all points make sure you have spares!
  • Check & lubricate all driveshaft U-joints.  If there is any question at all replace it.  Remember to check the center section of any constant velocity (CV or double cardan) joints.  Make sure you carry spares and the correct tools to service U-Joints.
• Check splines & slip yokes - lubricate.
  • Check all slip yokes and splines.  Lubricate splines.  If you have a tailcone slip yoke check housing for cracks, carry something to seal the tail cone if it gets damaged on the trail.
• Check for straightness, dents, and make sure all balance weights are attached securely.
  • Check all driveshafts for damage and straightness.  Make sure your balance weights are securely attached.  An unbalanced or damaged driveshaft at speed can cause serious vibrations problems, destroy U-joint and even cause significant damage.   Any local shop can straighten or repair a damaged driveshaft and balance your driveshaft if needed.  If a weight (usually welded on) has been knocked off or if you have a history of replacing U-joints or a bad pinion bearing it is a good idea to have your driveshaft serviced.  Don't ignore the front driveshaft!
• Check U joint straps / u-bolts
  • Check all U-bolt straps and/or bolts.  Use nylock nuts or lock-tite on them and do not over tighten U-bolts - they can crush the U-joint bearing.  Always carry a spare set of all types of straps, U-bolts or other bolts used on your vehicle.

Transfer Case

• Check output pinion for play.
  • Any side to side motion is bad and usually indicates a bad pinion bearing.   Check seals for leaks.  Check U-joints & straps.
• Visually inspect case and shifter mechanism.
  • Check for any possible problems such as interference, wear or damaged connectors or e-clips.
• Make sure all caps/seals are in place.
• Check for ease of shifting.
• Change fluid & inspect fluids for chunks of metal.
  • Change the fluid, remember to replace it with the correct type of fluid - chain driven cases often use ATF.  Some metallic powder would be normal, but chunks of metal are not.
• Check indicator & speedometer connections.
• Check vent lines.

Transmission (manual)

• Visually inspect case and shifter.
• Make sure all caps and seals are securely in place.
• Check vent lines.
• Check for ease of shifting & synchros.
• Check clutch, linkage & pedal.
  • On Jeeps or 4x4s with hydraulic clutches check clutch fluid, fill as necessary and bleed clutch lines.  Check clutch lines for damage or leaks.
• Change fluid and inspect fluids for chunks of metal.
  • Change the fluid, remember to replace it with the correct type of fluid.   Some metallic powder would be normal, but chunks of metal are not.  Sometime synthetic fluids and/or additives can help troublesome shifters.
• Check reverse light connections.
  • Check connections, make sure the reverse lights operate correctly.   This is important when you are running a trail in a group.

Transmission (auto)

• Visually inspect case and shifter
• Make sure all caps and seals are securely in place
• Change fluid and inspect fluids for chunks of metal & "burned smell"
  • Change the fluid, remember to replace it with the correct type of fluid.  Some metallic powder would be normal, but shavings or chunks of metal are not.
• Change filter if necessary.
  • Changing the fluid and filter can often help troublesome transmissions.   Even though many service manuals do not require it is a very good idea to do it periodically on your 4x4.
• Adjust bands if necessary.
• Check all electrical connections.
• Check vent lines.

Electrical / lighting

• Inspect and replace battery if needed. Fully charge battery.
  • Your battery is a critical lifeline, it starts your rig, runs your winch, keeps the lights on and when your alternator fails even runs the ignition for a while.  
• Inspect and replace and damaged or corroded wiring. Clean all cable connections (esp. at battery and ground straps).
• Check all lights for proper functioning, replace cracked lenses or assemblies.
• Check fuses and the fuse box and carry spare fuses of all ratings.  If your vehicle uses a fusible link anywhere - carry a spare.
• Check headlight aim.
  • Don't be one of those yahoos who fail to properly aim their liftend vehicles headlights and blind oncoming traffic (another reason for anti-4x4 backlash & legislation).  Keep the light aimed properly and on the road where you can use it.
• Check alternator connections, output and voltage regulator. Carry spares if needed.
• Check CB radio wiring & antenna. Tune your radio and antenna if needed.

Cooling system

• Change radiator fluid.
  • This should be done once a year.  Inspect the old fluid for signs of corrosion or rust.  If your fluid is discolored and rusty, thoroughly flush your system before adding any new fluid (and be prepared to replace your water pump in the not too distant future). 
• Clean fins and check radiator for leaks, repair any problems or bent fins.
• Check condition of all hoses & clamps, carry spare or patches.
  • Replace any cracked or swollen hoses and any bad or corroded clamps.
• Check and replace thermostat if necessary.
• Make sure your fan & fan clutch (or electrical fan) are working and that your fan has a fan shroud.

Steering

• Check all components for looseness, cracking, damage or corrosion
  • This includes everything from the steering wheel down to the steering arms.  Replace or repair any damaged component.  Pay particular care when inspecting the steering box and it's attachment to the frame.  With over sized tires look for cracks around the steering box mounts.  Check steering drag link and tie rod for straightness and dents.  Any dent is a weakness that can pretzel the component when stressed on the trail so fix it ahead of time.  [Click here for a cool drag link trick]
• Lubricate & torque all components.
  • Check all steering components bolts and nuts and make sure they are undamaged and are tightened correctly.  Check adjustment sleeves & threads, ball joints, etc.  Make sure that any crown nuts have cotter pins installed and carry spare pins.
• Check power steering fluid, belts and hoses.
  • Belts and hoses should be undamaged, belts should be tight.
• Check pump and reservoir for leaks.
• Check for "burnt" fluid. Replace or fill with power steering fluid as necessary.
  • Replace the fluid if you detect a "burnt" smell. It's always a good idea to carry spare power steering fluid.
• Check for interference with all components - especially during articulation or full steering lock.
• Check alignment or get vehicle aligned.

Engine

• Clean it.
• Inspect all of it for leaks, cracks or damage.
• Change oil and filter.
  • Inspect used oil for large metal particles or contaminants such as radiator fluid.
• Tune your engine & replace and filters or other components.
• Check spark plugs, distributor & wires.
  • It's always a good idea to carry spare ignition components
• Check all vacuum & emission lines & hoses.
  • Check all lines and hoses. Correct any vacuum leaks.
• Tighten belts - carry spares.
• Clean carb or injectors. Check all electrical & throttle connections including TPS.
• Check starter -
  • Check for worn gears, poor engagement, bad or corroded connections.   Correct any problems.  If you have an automatic transmission it is always a good idea to have a spare starter on the trail.

Safety

• Check seat belts and mounting bolts for all passengers.
  • Pay particular attention to the condition of the body where the bolts mount (looking for rust, corrosion or weakness) and frayed or worn seat belts.  Clean and lubricate retractors and latch mechanisms.
• Inspect & tighten seat mounting bolts.
• Replace windshield wipers and fluid.
• Inspect tub / body for corrosion or rust in critical areas.
  • Body mounts, firewall, seat mounts, roll cage mounts, floor board, etc.
• Inspect roll cage or "sports" bars.
  • Not just the condition of the cage or bars, but the body where the mounts are and all welds.
• Clean the inside out.
  • You don't want to truck your trash halfway across the country, have it get in the way of your pedals, or flying around when you are on the trail, or hitting you in the back of the head when you stop.  You probably don't have room for all the stuff you need to take, much less any extra trash in your vehicle.  Clean the insides of any windows and your rear view mirrors.
• Check your first aid kit and replace any needed first aid items.
• Check all winch components, cables and hooks.
  • Check all electrical connections, your winch controller and your winch.   Run all of your cable out and rewind it carefully and evenly checking for frayed or damaged cable while doing so.  Make sure your winch kit is complete with heavy leather gloves, tree saver strap, chain, a good heavy clevis shackle or two and a good pulley rated for your winch.
• Check tow hooks, recovery points and their mounts.
  • All vehicles need good attachment points front and rear, adequately mounted and in good condition.
• Check tow strap condition.
  • Check for cuts, frays or mildew - replace damaged strap before leaving.   Make sure you have a blanket or coat to throw over the strap or winch cable when using it.

Other

• Inspect, clean and lubricate high lift jack & mechanisms.
  • Clean any dirt or rust, particularly on the locking pins, and lubricate the mechanism.  A good white lithium grease works well.  Run the jack up and down and make sure it is working well and all parts are moving freely.  Carry a large solid base, such as a piece of 1" or 3/4" plywood (about 1 foot sq.) than can be bolted to the base to stabilize the jack.
• Check all spare parts and tools.
  • Carry all the spare parts and tools that you think you might need on the trail.  If several similar vehicles are on the same trip, they can team up to carry common spares and tools and thus save space.  Make sure all parts and tools are readily accessible in all situations.  It does no good to have them in a place you can't get to because of the position your vehicle is stuck in.  Make sure that you have highway flares as well - sometimes breakdown don't happen on the trail and don't happen on the road shoulder - don't get killed trying to fix something with your rear hanging out into the fast lane.  They work great at signaling search and rescue too!  If you belong to AAA or some other roadside rescue service - take your card with you.  If you have a cell phone, take it and make sure it stays charged.
• Check gas tanks and jerry cans. Make sure you have spouts & siphon hose. Use new gas and gas preservative in cans.
  • Make sure your spare cans are filled with fresh gas and use gas preservative in them.  You don't want to have problems with the gas when you really need it, use the highest grade and quality of gas you can get in your jerry cans.   Make sure your cans are in good conditions, seal well (you don't want gas spilling out when you get off camber on the trail) and that you have spouts for the cans and a length of usable siphon hose.
• Make sure that everything can be secured properly in the vehicle.
  • On the trail anything that is not securely fastened down will go flying (including you!) - so fasten absolutely everything down.  To help you with the exercise just imagine what everything that you put in your rig would feel like hitting you in the head, at high speed or when you are in a rollover.  Make sure it is not only fastened down, but fastened down well.
• Maps.
  • Find your way there and find your way back home again.  This is important because is strange terrain at night or without recognized landmarks it is very easy to stray far off course.  This is even true on the streets, if you don't know where you are or how to get where you are going then just having street signs does not help much.  I live in the Sierra foothills and if you did not know the area like the back of your hand and took a wrong turn at night you could end up lost for hours and a hundred miles or more from where you wanted to be.  No businesses are open to ask directions and no gas stations are there to fill you up when you get close to empty.   Play it safe, carry or buy a map for whatever area that you are in.  Not just USGS topo maps, but street maps too.
• Emergency money.
  • Again the voice of experience speaks.  Always carry spare money, cash, credit cards, ATM cards and whatever else you might need stashed both in your vehicle and somewhere on your person.  Perhaps the most stuck I have been was a several hundred miles away from home, at night in the dead of winter (Winter Fun Fest - 98) with an almost empty gas tank, and my wallet gets stolen with everything I had in it.    I lucked out then, but since that time I make sure I only carry what I absolutely need on my person and have an emergency stash locked in the vehicle.
• Spare keys.
  • You will never feel more stupid until you find yourself stuck on the trail because you dropped your keys down a cliff, into a crack or fissure in a mountain, in a mud bog or down into a deep river and you can't get your vehicle going again.  Only carry the keys you absolutely need with you on the trail and always carry a spare set of keys securely in the vehicle.  Your local AAA locksmith does not make it down many trails and when he does I am sure there is a significant extra charge!
• Food & Water.
  • Carry enough emergency supplies, including food and water so if you find yourself stuck on the trail (or on a deserted highway) for a day or more you can get by.  If you are likely to be in cold or hot weather also make sure you have reasonable clothing and shelter to handle any emergency.  If you think you may have to walk it out, make sure you have a way (like a small backpack) to carry food, water and supplies with you.
• Shoes.
  • Let's face it, your shoes are your ultimate backup.  When you are stuck, can't fix it and help is not on the way you may have to hoof it out.   Make sure you have comfortable shoes that are reasonable for hiking a good distance in the terrain and weather you may find yourself it.  Sandals and flip-flops don't qualify - a good set of hiking boots can save your tail. 

Excerpt from http://www.off-road.com/jeep/

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