Thought it would be fun to compile a list of the the more common things likely to break on the trail that will prevent you from getting home... then maybe discuss the symptoms, and what to do for each one.  Some of the more obvious ones to me are:

• Punctured Tire
• Break a tire bead loose
• Broken U joint (or rotoflex)
• Broken half shaft (Land Rovers anyway)
• Split hose
• Serpentine Belt (Land Rover) - or "Belts" plural for other makes/models
• Dead battery
• Punctured radiator
• Pinched exhaust

 What have I left off?  Brakes, steering, other?

Edit:  Additional items contributed in thread below:

• Broken Differential
• Fried Inertia Switch
• Bent tie rod
• Punctured fuel tank
• Punctured oil pan
• Blown fuses and Relays
• Motor Mounts
• CV joints

Starter, fuel pump, water pump, alternator, sensors, ECU, etc can of course fail too but aren't likely to fail specifically because the vehicle is on the trail.  Every vehicle that goes offroad for extended periods needs to be meticulously maintained.  Still, depending on the trip, age of these components, and necessity to limping home they should each be considered.

Broken windscreens. Had two of them so far in my experience.

 I knew a jeep owner that kept various things that need grease (CV joint, Bearings, etc) in those seal-a-meal bags in his tool box. It is virtually impossible to keep all the spare parts on hand in the vehicle that one might need. Traveling in groups does insure that someone will have the 'part' that is needed by someone, and that seemed to be the answer when the trip to Alvord was planned by this group.  

The man in Australia that we know as 'Professor Pinz' carries spare Landie parts in his 6x pinz for his friends when they go on long adventures down under. The hole in the fuel tank is infamous for pinzies and can sometimes be fixed with a bit of rubber and a sheet metal screw. There is a molex connector that is the bane of almost all pinzies and can be fixed by removing (uncoupling) it and using WD-40 to clean it up. Poor (failed) grounding is a major issue for most electrical problems on pinzies.  Also bent tie rods are a curious problem as pinzies have good clearance, but it does  happen, I have seen it.

I do carry spare belt (air cooled engine), bulbs, and some electrical items along with oil, wire and duct tape and most of the tools necessary to fix all but the most expensive problems. 

Diagnosing the problem, except for the most obvious like blown or a debeading tyre, is sometimes the real issue. Like when Paul's right front was smoking and it was curious as to what was the cause.

Happy trails.

I included flat tire and dead battery because they are literally the most common items that prevent someone from getting home.  Multiple flat tires in one day isn't uncommon when offroading.  Flat tires can usually be repaired, and dead batteries can be re-charged after getting a jump (from another vehicle or a jump box).  A truly dead battery that wouldn't take a charge at all would be a really bad situation if one were alone.  Deep cycle batteries and regular maintenance (checking battery condition) both sound like a good deal from an offroad reliability standpoint.  I've run my battery dead twice.  Both times were due to the Discovery 2s penchant for sucking the amps when the key is in the accessory mode... I digress.

Yes, one can be overprepared, and that's what my reply to Morris was addressing. From an expedition travel perspective (vs a trailer pulled trail rig relatively close to the tow rig) I think you need to bring know how and the small parts or tools/stuff (JB Weld, patch kits, etc) that allow you to limp home. Upgrade the weak points that you don't want to carry, and be meticulous about maintenance on the rest of the items.

Or being more concrete in my examples: A tie rod/tie rod ends can be upgraded so it won't bend. If you are still worried the tie rod ends are small to carry and A bent tie rod can be fixed in the field by first bending it back, then sleeving it with a hilift jack handle, and welding it in the field. A broken U-joint can either be swapped in the field or the driveshaft can be pulled and the truck driven out in 2WD. If the diff is broken the driveshaft can be removed and/or axles can be pulled (full floaters) with small to carry stubs put in their place. Each item in the truck can be considered and a plan to fix/replace/remove can be forumlated ahead of time. It's amazing how much stuff can be fixed with a relatively small amount of parts.

The purpose of this thread then is to identify those items that will truly keep you from getting off the trail and identify how to make a field repair. There are many many things that can go wrong with a vehicle, but not all of them actually prevent us from getting off the trail and back to a USFS road where a tow truck can meet us. E.g. A bad coil pack won't usually completely disable a vehicle, but a fuel pump on a modern car will.

I'm curious as to what others think but looking back over the various items being posted (not just your's Jay) there are several that I wouldn't personally prepare for.

Trailer hitch: Unhook the trailer, drive out, get a new ball, and come back for the trailer. Leave someone behind if necessary to watch the trailer.

E-brake: Doesn't seem to impeed progress.

Shock mounts: Pull the shock if necessary, but again it doesn't sound like it would impeed progress... just makes for a bouncy ride.

Fingers: Clearly you just need to bring a spare finger or two. I recommend chicken flavored fingers. You can nuke them in Todd's microwave.

Snow chains: A broken snow chain could take out another part, but the lack of snow chains themselves usually slows progress more than completely stopping progress.


Wheel studs: Did you break all 5 studs? It seems like 4 would keep the truck rolling down a trail anyway.

Broken Frame: With moderate trail use, and w/o being overloaded, this is very unlikely on a truck made for offroading. while there is no guarantee, I'd also assume that the truck could be driven until it was off the trail and back to a tow truck.

Clutch failure: Real potential problem here. I'd consider this an items to avoid via proper maintenance.

Broken Axle: Common, easy field repair/removal on most trucks, already in the list.

Steering box: I don't believe this will disable the vehicle. It will lose power steering, but believe it will still be drivable. Not sure though as I don't know diddly about steering components.

Motor Mounts: Good one Dave! Common, small, and field repairable.



 

I don't think "Starter" should be on the list... well, it is something that will prevent one from getting home but isn't "common" and is IMHO something that should be replaced preventatively based on life expectancy of a particular vehicle. Alternator, fuel pump, oil pump, water pump, timing chain, all fall in that category to me.
 

I was thinking of what could prevent me from coming home if I don't have spares. My only significant breakage on trail in 10 years was rear axle shaft. I locked my ARB and drove 150 miles home in full time 3WD. Ignition coil misbehaved after past headlight mud dipping for about 10 min, despite being very appropriately located at very top of engine. Fortunately it somehow dried up and I made it home only to completely fail in couple weeks. So electricals could bite you. Not mentioning that article by Tom Shepard in Overland Journal

Hi Craig, I know you've purposely left off a water pump but I like to carry one. I've personally needed to replace one on the trail and two other friends have lost theirs over the years. No coolant brings things to a stop right away and the part is not too big to carry. I'm glad that relays, fuses etc. have made it in, on some trips I've handed out fuses like popcorn.

Bill