In contemporary 4-wheel drives, the capability to switch between 2WD and 4WD is a safe maneuver under specific conditions—typically when speeds stay below 62mph (100km/h) and the vehicle operates on low-traction terrains like snow, sand, or muddy tracks. However, what if the vehicle remains in 4WD mode inadvertently while transitioning back to the tarmac? Have you noticed a jerky sensation during cornering or an unexpected resistance in the transmission? Let’s find out why your 4-wheel drive jerks when turning.
Extensive driving in 4H with a part-time 4WD on a high-traction surface, or with the center diff locked with a permanent 4WD, will result in driveline components such as u-joints, axles, transfer-case gears, bearings, and drive-shafts seizing up and failing.
Let’s dive more into drivetrain wind-up and why your 4WD jerks when turning
Table of Contents
4-Wheel Drive Jerks When Turning: DRIVETRAIN BINDING
Extended 4WD use on high-traction surfaces causes stiffness, jerky steering, and severe under-steer due to drive-train wind-up. Avoid prolonged 4WD engagement on high-traction surfaces to prevent drive-train damage and difficulty shifting back to 2WD mode.
4WD Binding – How To Fix Transmission Wind-Up
If 4WD remains engaged on asphalt, it leads to transmission wind-up, noticeable if gears jam. To address this, park with two wheels on asphalt and two on a slippery surface. Alternatively, try reversing in the same direction. Seek inspection by a drivetrain specialist afterward.
Understanding Part-Time 4WD Systems
Part-time 4WD systems have differentials at the front and rear axles. The lowest part, the “pumpkin,” houses the differential. In 2H mode, power goes from the engine through the transmission and rear driveshaft to the rear differential, splitting power evenly to the rear wheels. While driving straight, differential gears rotate as a unit. However, when turning, the gears inside allow the wheels to rotate at different speeds.
Engaging 4WD connects front and rear axles, sending equal torque to both driveshafts. Turning causes differences in rotational speeds between the front and rear wheels, affecting the driveshafts due to varying wheel speeds. Uneven tire wear or inflation pressures can also cause speed differences between axles.
Understanding Full-Time 4WD Systems
In a full-time AWD, power is consistently delivered to all four wheels. It distributes power evenly but can adapt depending on road conditions. The AWD system aids acceleration and turning but does not improve braking on slippery surfaces. Installing winter tires enhances braking, and turning, and assists stability systems.
In off-road conditions, 4H is ideal since the differences in rotational speeds between the front and rear driveshafts can be absorbed through slippery conditions and tire slippage caused by uneven surfaces. So for it to function properly, there needs to be a small level of slippage.
On firm, dry road surfaces, only 2WD or 2H should be engaged with a part-time 4WD, or in the case of a permanent 4WD, the center diff lock should be disengaged and unlocked. This will prevent tire damage, excessive fuel consumption, and expensive damage to drive-line components.
Understanding How Differentials Work
Differentials are an integral part of every 4-wheel drive. The wheels receive torque from the engine via a driveshaft. The main function of the differential is to allow both wheels on the axle to turn at different speeds when turning. When cornering, the wheels on the outside need to rotate at a higher speed versus the wheels on the inside of the bend. if the wheels were joined/locked by a solid driveshaft then the wheels would have to slip to successfully turn. The clever gear design inside the differential allows the left and right wheels to safely turn at different speeds. Hence the term “Differential”
Torque from the engine is transferred to the ring gear (a component inside the diff) through a pinion gear. The ring gear is connected to a spider gear which is located at the heart of the differential.
Spider gears are allowed to make 2 kinds of rotation.
- Along with the ring gear
- on its axis
The spider gear meshes with 2 side gears so power flows from the engine via the driveshaft to the left and right wheels via the ring and spider gears inside the differential.
The Differential Has Other Functions
- Speed reduction at pinion gear assembly
(results in torque multiplication)
- Turn the power flow direction by 90 degrees
(transfers the torque by 90 degrees through the side shafts to the wheels)
The above-mentioned explanation is of a standard, open differential found on most trucks. It does have the drawback of being an open diff though which means that if one wheel is on a surface with good traction and the other is on a slippery surface without traction, the standard open diff will send the majority of the power to the slippery wheel. This is because torque always follows the line of least resistance. This can make the vehicle become temporarily immobile, aka STUCK! To overcome this problem, vehicle manufacturers have introduced 3 solutions.
|Differential lockers||Mechanism that physically locks the differential, ensuring both wheels on the same axle rotate at the same speed|
|Traction Control (TC)||System that manages wheel spin by applying braking or reducing engine power to maintain traction in slippery conditions|
|Limited slip Diffs (LSD)||A mechanism that physically locks the differential, ensuring both wheels on the same axle rotate at the same speed|
Never engage your 4WD on dry pavements. You will destroy your drive-train components and cause severe tire damage very quickly. Always remember to switch a part-time 4WD back to 2H when you leave the gravel or sand and before you get back on the tarmac. If you are driving a permanent 4WD on a high traction surface, always make sure the center diff is unlocked.