Center Axle Disconnect
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A center axle disconnect system or CAD is an alternative to
locking hubs Locking hubs, also known as free wheeling hubs are fitted to some (mainly older) four-wheel drive vehicles, allowing the front wheels to rotate freely when disconnected (unlocked) from the front axle. This is done to reduce the mechanical resist ...
. CAD systems are typically used in
front drive Front-wheel drive (FWD) is a form of engine and transmission layout used in motor vehicles, where the engine drives the front wheels only. Most modern front-wheel drive vehicles feature a transverse engine, rather than the conventional longitu ...
axle An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearing ...
s on
four wheel drive Four-wheel drive, also called 4×4 ("four by four") or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer case ...
vehicles. A CAD system works by having an axle shaft (typically the longer shaft) split into two pieces. One piece is connected to the carrier, the other connected to the wheel. This reduces drag on the axle by allowing only the spider and side gears to spin, while the differential carrier,
pinion A pinion is a round gear—usually the smaller of two meshed gears—used in several applications, including drivetrain and rack and pinion systems. Applications Drivetrain Drivetrains usually feature a gear known as the pinion, which may ...
and
drive shaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power (physics), power and torque and rotation, usually ...
are at rest (as is the inner portion of the disconnected long shaft and its associated side gear). The axle is engaged by connecting the two split axle shafts. The ends of the axles are typically splined and use a collar to connect the two shafts together by sliding over both shafts.


Comparison with locking hubs

Although a widely used system, this system is not as efficient as a system with locking hubs. A CAD system spins the axle shafts, spider gears, and side gears in the carrier during normal driving. Locking hubs disengage the axle at the wheels, allowing all of the axle to be at rest during normal driving. Nevertheless, a CAD system still makes for much less drag than having the axle completely locked in (which would spin the axles, differential, driveshaft and part of the internals of the transfer case). Like locking hubs, the CAD system is designed to improve
fuel efficiency Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device, wh ...
of the vehicle. Other, often debated, benefits of CAD systems are reduced vibration, axle wear, and noise, as well as improved steering and drivability.


Advantages and disadvantages

Unlike locking hubs, CAD systems are generally automatic and engaged when the vehicle is placed in four wheel drive. Due to the lack of driver control over the CAD, it is not as well known to the public as manual locking hubs are (but no different from automatic locking hubs in terms of driver involvement, and manual hubs are rare on modern 4x4 vehicles). Locking hubs are obtrusive and damage can occur that can cause the four wheel drive system to fail — damage that would not be an issue in a CAD system. However CAD systems are mostly vacuum controlled and damage can occur to the vacuum system and to the CAD itself. Rotting of vacuum lines will cause the four wheel drive system to fail — damage that would not be an issue with locking hubs.


Later CAD systems

Ram Truck The Ram pickup (marketed as the Dodge Ram until 2010) is a full-size pickup truck manufactured by Stellantis North America (formerly Chrysler Group LLC and FCA US LLC) and marketed from 2010 onwards under the Ram Trucks brand. The current fi ...
s used the CAD from 1994-2001. In 2002 it was phased out of the 2500 and 3500, leaving some late models without a CAD system. Ram 2013 model year trucks began using a CAD system again, this time electronically controlled instead of vacuum.


External links


4x4Wire: Center Axle Function and Trail Repair ExplainedG2 Axle & Gear: A Thru D on Gear & Axle-related products.
{{DEFAULTSORT:Center Axle Disconnect Automotive engineering Automotive accessories