4x4 Partime Question

d2alio · October 21, 2003

One thing i never quite understood is why the 4x4 on the 2500 HD is described by GM as "part time". What the hell does that mean? Does the truck just decides on its own when to use all wheels? And, if that's the case, what "times" will the truck do that?

k1500chevy97 · October 21, 2003

part time is the truck is in 2wd until you shift it into 4wd

Shaners · October 21, 2003

AutoTrac (which is not available on the 2500HD) would be considered part-time 4wd. When in the AutoTrac mode the truck is in rear wheel drive until it detects wheel spin, and then it switches over and engages the front wheels for added traction.

For the HD's I don't know what "part time" 4wd would be, unless it means that you physically have a choice between 2wd or 4wd as opposed to AWD like the new SS Silverado has. (Like K1500Chevy97 explained)

robsawatsky · October 21, 2003

There isn't any official terminology but in general:

Permanent or Full-time 4WD or AWD: All 4 wheels are always driven. Various forms of centre differentials (i.e. between drive shaft to front-rear) and viscous coupling are used to manage torque split between the axles and to accomodate different front/rear turning radius without binding the drivetrain. Some offer a locking centre diff for poor traction situations.

Automatic 4WD or 2WD - Either a part-time or full-time system where the engagement of the front/rear axles is electronically controlled. Usually part of a selectable 4WD/AWD system.

Selectable 4WD - Allows for combinations of auto, 2WD, 4WD and possibly others. Must have an electrically shifted transfer-case for part-time systems.

Part-time 4WD - Manually or electrically selected 4WD system designed for low traction use only. Usually, no centre differential so cannot be used on dry pavement.