4WD Glossary

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© 1996-2005 Harald Pietschmann



Four wheel drive systems
"Full Time 4WD" 


Full Time 4WD
also called permanent 4WD and constant 4WD

Main mode is 4WD. 4WD is used full time.

No 2WD mode available.

All four wheels are powered at all times
. Operates well on dry pavement due to a center differential or equivalent device (planetary gears, etc).

Part Time 4WD does not have a center differential.


A center differential is essential for on-road use but can be detrimental for off-pavement use. When leaving pavement the center differential needs to be disabled (locked). It either locks automatically* or it has to be locked (disabled) manually.

Normal setting for on-road use and light duty off-road use is 4WD "high", also called high range.

For more torque 4WD "low", also called low range, is available. Low range provides substantially more torque to the wheels and allows slower speeds than in high range. 4 low does not provide more traction - it only provides more torque.

Full Time 4WD requires:

a transfer case

a center differential

two drive shafts

two axle differentials

two powered axles

*) With either Torsen, viscous coupling, Haldex or Gerotor coupling

part time 4WD - all wheel drive - automatic 4WD - combination systems

| 2WD use of traction | 4WD layouts | crawl ratio | 4WD components | do you need 4WD? |

Learn from 4x4 professionals to get the most from your 4WD investment:

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