The Mystery of All Wheel Drive

Thursday, November 9, 2017

I know more and more of you have checked the AWD option box in one of your more recent automotive purchases. These types of vehicles pass through our doors more and more.  Many manufacturers even now offer all wheel drive versions of a lot of their cars. Not just Audi and Subaru. Heck who even drives a car though? All wheel drive sport utilities (SUVs) are now the vehicles of choice.

 

The decision to own an all wheel drive vehicle has its perks but it also comes with some likely unwanted side effects. These vehicles are heavier and more complex than their two wheel drive counterparts.

 

Certainly as technology progresses these all wheel drive systems work better and better. Their operation is so seamless one would be hard pressed to recognize anything extra is going on below them. I remember the AMC Eagle. That was one clunky beast. Nevertheless I knew a few Kootenay dwellers that revelled in their Eagle’s slippery road agility and more car than truck like demeanor.

 

Every all wheel drive vehicle has two extra drive axles and one additional drive shaft. Then there is an angle gearbox or possibly a transfer case. And don’t forget one extra differential. This is an extra one hundred to two hundred pounds of stuff. Somewhere within these added parts will be a device that allows the front wheels and rear wheels to rotate at different speeds. It may be an electronic clutch pack, a Haldex, or even a silicone fluid coupling.

 

These extra parts need to be inspected and maintained on a regular basis. Axles typically are the CV joint variety. Admittedly modern day CV joints are tough and maintenance free. The CV or ‘constant velocity’ joint has replaced the U joint of old. It allows rotation of a shaft at various angles. There is typically one CV joint on either end of the axles. The joint is bathed in grease that is held in place with a plastic/rubber boot. These joints are generally service free unless the boot tears or gets ripped open allowing the grease to be flung out and the water, salt, and dirt to get in.

 

Catching a torn boot during a vehicle inspection can mean the difference between replacing a whole axle or just a rubber boot and some grease. In both cases axle or boot replacement requires significant labor.

 

That extra differential, be it up front on a rear wheel drive vehicle or at the rear of a normally front wheel drive vehicle, has its own maintenance requirements. Regular fluid level and fluid quality inspections are necessary. There is also likely a recommended fluid change interval. In many cases the fluid in these small differentials is some special stuff. Make sure you or your mechanic gets the right stuff. The differentials may contain fancy clutches that help distribute power to the wheel with traction. These clutches need the proper lubricants.

 

Angle gear boxes are typically found on front wheel drive vehicles that require a ninety degree change of power transmission at the front of the vehicle. Again these boxes are full of a special lubricant. The angle gear box is typically very small and contains very little fluid. Even a small leak will result in a dangerously low level that could seriously shorten that component’s life.

 

The Haldex, electronic clutch pack or silicone fluid clutch are the heart and soul of any modern day all wheel drive system. These components again require specialty lubricants to function properly and provide a long service life. It again is likely that the manufacturer requires regular fluid changes and in between those someone needs to be checking the fluid level and quality.

 

The magic of all wheel drive still requires regular maintenance or all that magic could cost you majorly.

 

 

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