Technical > Four Wheel Finesse
Bring 'Em Back Alive - Part 2
by Jim Allen
What do you do when you have a broken axle on a c-clip axle. Some years back, a group in Moab had such a thing happen and this was their “get it home” cure. The center pin was intact, so losing the other axle was not a danger. The brake drum was taped in place and a piece of wood was strapped to the bottom of the spring to act as a skid. This got the rig eight or so miles to where a truck and trailer could bring it all the way to civilization.
The emergency repairs outlined in this story are not offered as permanent, or proper. Combine them with common sense, judgement and use at your own risk.
We continue our discussion of mechanical “McGuyvers.” This time we will focus on drivetrain stuff. Most breakage is avoidable. Upgrading drivetrain components to suite the tire size, or downgrade tire size to preserve the drivetrain, are the two best ways to minimize the dreaded “snap-crackle-pop.”
Busted Rear Axles and Diffs
The first thing you need to know is whether you have a full or semi-float axle. If you have a semi-float, is it a pressed on bearing or a c-clip? If it’s a c-clip and you break an axle, STOP YOUR RIG IMMEDIATELY! A c-clip axle will allow the shaft, brake drum and wheel to part ways with the vehicle. This can happen fairly fast and cause more damage when it does, not to mention killing you in the process. The only safe-to-move c-clip axles are those that have rear disc brakes. In most cases, the caliper will prevent the axle from sliding out of the housing.
A broken front hub may be the most common drivetrain failure. In most cases, it’s the weakest part of the drivetrain. Fortunately, it is also one of the easiest to replace, assuming you have a spare, that is. Collateral damage is usually minimal, but it’s important to get the broken chunks out to avoid wheel bearing damage.
A vehicle with a pressed bearing axle is safe to move, but not safe to drive. All that’s holding the shaft in place is that pressed or screwed on collar... not something I’d trust my life with over a long distance or at any speed above a crawl. With a full-float axle, you’re perfectly safe to drive, but it’s advisable to at least pull the shaft and get the loose chunks out to avoid more damage.
Changing a rear shaft is fairly easy on the trail... except when it’s not. Most of the time, a rear axle breaks at the splines. That leaves a little stub stuck in the diff. It can be fished out through the axle tube with a long magnet or a finger tool. Sometimes the splines twist just enough to jam the broken stub in the side gear splines. On a good day, if you’re livin’ a wholesome life, it will pop out by prying from inside the diff, or using a long rod to snake through the diff (not always possible) and “punch it” through from the other axle tube. If you’re livin’ a life of self indulgent debauchery, sometimes even a shop press can’t get a broken stub out. Sometimes you have to drop the carrier to get a stubborn stub out.
If you break a few teeth off a pinion or ring gear, you can often continue on... carefully. However, you should pull out the broken chunks first. If you blow the spiders, or the locker, you can sometimes make a “Lincoln Locker” if you weld everything up. That requires a welder out in the field. A howling bearing can be nursed along, just make sure there is enough oil. There are many other potential axle failures, most of them permanently fatal.
Busted Front Axles/U-Joints
Unless your problem is related to the wheel bearings or steering knuckles, you can always go into two-wheel drive, unlock the hubs, winch or take a strap when you need to, and drive out to civilization on your own. Some people opt to do that rather than carry a bunch of spare parts or attempt a trail repair.
The Jeep D35 is notorious for its weak strap type U-joint yokes. Judging by the witness marks at the center of the driveshaft, it looks like the shaft struck the ledge and the bolts sheared. Once the axle end was loose, it flopped out of the slip yoke output and you can just see the pool of fluid. It is usually possible to fish out the broken stubs,and, with spare bolts and straps sourced from a spare parts box, along with recovered or spare T-case fluid, you can be on your way again.
A busted front u-joint is a common enough front end failure. The important thing to remember when it happens is to get off the fuel feed fast. The more the broken joint slings around, the more damage it does, and sometimes a busted u-joint can knock the ball joints apart and the steering knuckle falls off.
The failure modes of a front axle are usually very predictable. The hub is often the weakest link. It’s also the easiest thing to change. The U-joint or the inner ears will usually fail next, most often when the wheels are turned past 15 degrees. Increased angularity multiplies the torque load at the inner trunnions of the U-joint. After that, it’s a toss up between the outer shaft or the necked down section of the inner shaft.
When an axle U-joint fails, it often takes the ears of one or both yokes with it. The 4340 front shafts out there can usually handle a U-joint breaking if the driver gets off the fuel feed fast. Some people say they can save a standard axle with this light foot method too. I’m never that lucky and because one yoke is almost always tweaked, I like to carry assembled complete shaft(s) rather than U-joints or parts. It’s easy to slip in and it’s a complete repair. This way, you also know you have all the parts. You could also carry both inner shafts, loose U-joints and one outer because the outer stub-shafts are the same on both sides.
The broken off stub scenario, outlined in the rear axle section, can also happen up front. Also, when an outer shaft fails, it can also take out the spindle or spindle bearings, so it’s a good idea to carry a spindle seal kit containing the seals as well as a bearing and spacer.
Hubs are a very common failure, so carrying an extra is a good move. The full-time four-wheel drive rigs of the ’70s and ’80s that used Dana axles have a solid drive gear. If you can find them, they can be carried as a spare in lieu of a hub.
Busted Driveshafts/Driveshaft U-joints
Broken driveshaft U-joints are not uncommon. Sometimes the U-joint fails and sometimes the attaching hardware fails, such as the straps or U-bolts. Binding, due to excessive angularity, is a common failure situation, highlighting the need to check your driveline U-joints for binding on full droop after a lift.
A major part of this CV joint housing is broken, namely the mounting flange where it bolts up to the T-case. The root cause was binding at full droop.
The shaft itself can also fail, most often caused by impact on rocks. A spare U-joint of each type used on your rig always makes sense. Some people carry spare driveshafts, but they take up lots of space and add weight. The better tip is to have stronger-than-stock driveshafts built. Guys with underhood welders can sometimes repair a shaft well enough with scrap steel to keep going.
Sometimes the housing of a CV joint will fail, though usually the joints are weaker and fail first. Sometimes the center pivot wears out or breaks. A driveshaft CV is a bear to rebuild on the bench for those that don’t do it every day. In the field, it’s the grizzly of bears!
Ultimately, a failed driveshaft or U-joint may force the owner to remove the busted shaft and limp home on the other axle. That can be a problem on a rear driveshaft with a slip-yoke type t-case output. Remove the slip yoke and oil will puke out. Slip yoke caps are available for most t-cases. They are cheap and it makes sense to add one to your tool box if you have a slip yoke output.
Clutches and Manual Transmissions
The majority of clutch problems are with the release mechanisms, whether hydraulic or mechanical. If your hydraulic setup has a fairly slow leak, simply keep it full. In lieu of brake fluid, you can use ATF, power steering fluid or even motor oil (making sure you clean the system out thoroughly at repair time). Mechanical problems with the linkage can often be corn-cobbed to work. Ultimately, with either type of mechanism, you can start in gear and even shift without the clutch. You may end up having to go slow, but you can go.
U-joints are commonly changed out on the trail. It ain’t a cakewalk, but it’s doable. The main thing is to make sure the ears of the yoke are intact. If they are slightly tweaked, they can be filed and hammered back into shape, but consider that axle a “dead man walking.” Once tweaked, they are weakened and should be replaced.
A slipping clutch is more difficult. If you start smelling hot clutch, stop whatever you are doing and let it cool. If it smokes to the point of slipping, try to go easy on it by staying in low gears, taking a strap on the hard stuff and letting it cool often. If it fails completely, it’s strap time for sure. It isn’t practical to carry a spare clutch assembly, nor to change it in the field.
Sometimes a manual trans will scatter itself beyond a corncob repair. Sometimes it will fail leaving you with one or two gears to work with. Using the unit at this point may cost you more money down the road, so judge the effort of a tow out vs trying to drive it. If you decide to drive it, a good way to preserve what’s left is to drain the oil and get all the busted chunks out of the unit that may destroy what’s left. By observing what chunks come out, you also may be better able to see what happened and gauge the wisdom of trying to operating the unit.
Automatic Transmissions
The minute your automatic shows signs of overheating or slipping, STOP. Let it cool and then, on level ground, check the fluid level and its condition. Usually, once a tranny starts to slip, it’s a “dead man walking.” It may be slipping due to a low fluid level, so add fluid and check for leaks and repair them if you can. Cooler lines are a common culprit in this scenario.
An overheated tranny may slip or shift erratically until it cools. The fluid may boil out the dipstick in a “cherry volcano.” Let the unit cool, add fluid as needed and contemplate your immediate purchase of a trans temp gauge. If you are having recurring overheating problems due to trail conditions, keep in the lower gears (trans/t-case) and find less steep terrain if possible.
Water can kill an automatic in a jiffy, so stop and drain it immediately if it ingests some. It’s a good idea to install a drain plug in the tranny pan for this reason. If your tranny takes on water, stop, let the oil and water separate (it may take a while) and drain the water off the bottom via the plug. You may have to do this a couple of times because some water will be in the torque converter. Without the plug, you’ll have to drop the pan, and you know that’s a mess you want to avoid.
If the trans is slipping with a full fluid level, there’s not much to do but nurse it home or tow it. It may slip in one gear and not in another. Find a gear that does not slip and do your best to keep it in that gear. A slipping trans will overheat faster. The more it slips, the worse it will slip. Whatever you do, don’t change the fluid to try and stop the slippage. It’s counter-intuitive, but any tranny man will tell you that’s the fastest way to complete failure.