How a Driveshaft Functions
Your Wrangler’s driveshaft performs a crucial function in moving power from your engine to the wheels and transferring torque to the differential from the transfer case. Torque is the strength of your Jeep's engine (its ability to do work. A distinction from the horsepower, the speed at which work is done). A driveshaft transmits that raw power to the differential, where it can actually spin the wheels, moves your vehicle, and lets it do everything from skimming along a highway to surging out of mud hole on the trail.
Knowing when to upgrade your Wrangler's driveshaft is critically important because running the wrong shaft can easily result in breakage which stops your Jeep dead (potentially with disastrous results in traffic). An inadequate driveshaft can break some time after the stress has been applied too, Material fatigue adds up during wheeling, causing fractures that later prompt the shaft to snap even under light driving loads.
As a rule of thumb, a Wrangler driveshaft upgrade is very often required after any significant suspension lift or power increase is installed. Let's look at some of the specific situations that signal it's time to get an improved aftermarket driveshaft.
When to Upgrade a Wrangler's Driveshaft
The stock driveshaft is designed to match the suspension travel of the factory suspension. It is also not too tough (just enough for average driving and fairly mild off-roading) and lacks grease fittings due to cost cutting during the engineering process. Times to upgrade your Jeep's driveshaft include:
- After installing a suspension lift kit of 2.5 inches or more. Upgrading the driveshaft is mandatory with a 2.5-inch lift or higher. The stock shaft is too short to handle suspension travel and will break under stress. Probably sooner than later.
- After installing any lift kit. While low-rise lift kits of 2 inches or less technically function with the stock driveshaft, the shaft is still slightly too short for maximum suspension extension. At some point, while flexing far out of line, the lifted Wrangler will exceed the driveshaft's extension capabilities, suffering damage, or breaking outright. In addition, on 2012 Wranglers the driveshaft boot will come in contact with the exhaust cross pipe, requiring an exhaust spacer or new drive shaft.
- After any significant upgrade to horsepower. Engine mods that boost horsepower and/or torque might seem far removed from the driveshaft, but that extra power is transmitted to the wheels only through that specific part. The factory shaft lacks the toughness to handle boosted power, resulting in eventual failure if not replaced.
- After boosting tire size, or making any other improvement to the engine, drivetrain, or transmission. Bigger tires (which typically imply a suspension lift anyway) or changes to the drivetrain or transmission can also cause torque development outside the factory range. Installing an upgraded driveshaft heads off any problems before they occur, plus gives the modifications the support they need to provide their full potential improvements to your Jeep experience.
- When the stock driveshaft wears out or breaks. Since factory shafts can't be greased and feature a less robust build than most aftermarket counterparts, they wear faster. Their thinner metal and narrower diameter means they are more likely to snap under the stress and torque of an off-road adventure too. You can test for severe wear by accessing the driveshaft and seeing if there is play in it other than in the joints. If the driveshaft can be moved (other than where it's designed to move at the joints), then it is severely worn and needs to be replaced. If you are going to replace the stock driveshaft anyway due to wear or breakage, the best choice is adding a superior aftermarket part which supports future mods.
- When any modification changes the driveshaft's angle to more than 15 degrees. Under no circumstances should a Wrangler driveshaft ever run at an angle greater than 15 degrees – this is an absolute hard limit with no “wiggle room.” Beyond 15 degrees the driveshaft wears rapidly, functions under par, and suffers torsional vibration causing material fatigue leading to eventual sudden failure (that is, snapping). Get a longer driveshaft to reduce the angle under 15 degrees.
The Significance of an Aftermarket Driveshaft with Suspension Lifts
Installation of a Wrangler lift kit is the premier reason for also swapping out the stock part for an upgraded driveshaft. The driveshaft lengthens when the suspension stretches – that is, when the axles and wheels move downward away from the body – and shortens when the suspension gets compressed. The stock driveshaft simply isn't long enough to lengthen sufficiently when the wheels flex downward with 2 inches, 3 inches, 6 inches, or whatever additional travel the lift kit allows. Upgraded aftermarket shafts, however, are made to match the extra length.
- On newer 2012 Wrangles, the stock drive shaft will come in contact with the exhaust cross pipe after the Jeep is lifted. An exhaust spacer can be used to provide enough clearance, but a new thinner drive shaft is often a better solution.
- A stock driveshaft may actually rip free of the transfer case output or differential input such as when clambering over obstacles like rock slabs, steep stream banks, or large boulders when the suspension “stretches.” This not only stops the Jeep immediately, it can destroy the driveshaft plus the differential and/or differential case outright. This fact clearly shows the timeliness of installing an aftermarket shaft matched to the lift height of your lift kit.
- A double Cardan CV driveshaft matches up to both a Wrangler with a slip yoke eliminator installed, and to Jeeps with a fixed flange transfer case output. In either case, a built in splined sleeve provides the variable length in place of the standard slip yoke.
- For higher lifts, it may be necessary to change the differential's pitch to correct the shaft's geometry. Pointing the driveshaft's attachment point towards the transfer case output will help “level out” the driveshaft angle.
- Many high quality aftermarket shafts feature thicker, more rugged tubes able to handle the rigors of extreme off-roading combined with horsepower boosts. At the same time, these designs reduce the overall diameter so the shaft won't cause problems with either stock or high clearance exhaust systems (though exhaust spacers may still be required).
Extended Front Driveshaft for 07-11 JKs
Wrangler CV Driveshafts, Off-Roading, and Grease
Typically, stock Wrangler driveshafts have no grease fittings. This means there is no way to slow down wear, or to expel grit from the interior workings of the joints after wheeling in dusty, muddy, or sandy conditions.
When you go wheeling frequently in gritty, dirty situations (often the places where the most fun and adventure is to be had), this is another occasion when a driveshaft upgrade will probably serve your Wrangler well. This applies even if you have not yet installed a suspension lift:
- Practically all modern driveshaft upgrades include grease fittings. If you grease the driveshaft regularly, squirting grease into the fitting at one end until clean grease flows out of the fitting at the other, this clears grit and dirt from the driveshaft's working parts, greatly extending its life even in the filthiest off-road environments.
- Greasing the front end driveshaft and running your Jeep in 4-wheel drive at least 30 minutes monthly slows front driveshaft wear even if you usually use 2-wheel drive.
- Installing an aftermarket performance shaft prepares the way for adding a lift kit at a later date.
So What's the Difference Between Two-Door & Four-Door JKs?
A two door JK Wrangler has a wheel base of 95.4” opposed to a four door that has a wheel base of 116”. Those extra 20.6” of wheel base have a dramatic impact when it comes to stance, handling, lift modification, and most importantly, driveshafts. The front half of the Jeep is the same between both models, therefore the length of the front drive shaft and angles when the Jeep is lifted are all the same. The difference is noticeable in the rear half of the Jeep as the rear axle of a four door sits further back. As a result, it uses a longer drive shaft. Considering Wranglers are primarily a rear wheel drive vehicle, this has a tremendous impact if you decide to lift your Jeep. The angle created for this rear drive shaft changes drastically between two door and four door models and requires replacement at different stages.
Can Modifying My Suspension Help My Driveshaft?
One way to correct suspension geometry is to correct axle position with new control arms. Control arms push the axles out in an effort to re-center them within the wheel well. But this introduces another stress point for the stock drive shafts as the axles are pushed further out. The drive shafts need to be longer. Under nominal lift heights ranging from 1.5”–3” there isn’t a noticeable impact in the positioning of the axles. Under those cases, either a top or bottom set of control arms is enough to push the axles back slightly, but more importantly correcting their angle. This then brings the drive shafts inline and alleviates any stress on the joints. It’s important to note the stress along the length of the shaft should still be monitored.
Lower Control Arm Installed on a JK
What Size Lift Can I Safely Run on My JK? Two-Door & Four-Door
As stated earlier, the front drive shafts are the same between the two and four door models. When lifted, the angle they create is the same. As a result, a good rule of thumb is to maintain within a 2.5”-3” lift range for the front. Remember, Wrangler models 2012 have the potential of rubbing against the exhaust that crosses under the drive shaft. You’ll need the spacer mentioned above to preserve your driveshaft. It’s important to note lift height estimates are based on a fully loaded Jeep. This means a Jeep equipped with steel front and rear bumpers, winch, and skid plates. Since the bulk of additional weight is largely concentrated in the front, the Jeep tends to have a bit of a rake. You can counter the rake look with different spring rates between the front and rear.
The rear drive shaft introduces a difference between the two and four door models. In four door models, the rear drive shaft is longer and able to accommodate a higher lift amount, generally 3.5”–4” of lift. For a two door wrangler the maximum lift should be 2.5”–3”, similar to the front. Again, these lift estimates are based on a fully loaded Jeep. The reason for the difference is due to the length of the drive shaft. On two door models a shorter drive shaft produces more of an angle than a four door with the same lift height. This greater angle has the potential of contact and joint/boot damage while driving or out on the trail.
If you plan on taking your Wrangler off-road, the problem of angles and contact increase greatly, especially if you do a considerable amount of articulation. Large drops or compressions flex the wheelbase and put a big strain in the joints of the drive shaft and substantial angles can cause serious damage to the drive shaft or drive train.
JK on a 4in Suspension Lift
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