part time 4wd

[ford ranger]

My truck is part time 4wd and I cant use it on dry pavement. from what I read in the book because it binds and may break something, I can understand if you had lockers in but mines open So doesnt it open when u make a turn to allow for different wheel speed . thanks


07 4x4 ranger XLT 4.0l 8.8 3.73

 

[Todd]

Torque windup in the drive line occurs when you drive a 4 wheel part time vehicle on a high traction surface. Between the axles there is differentiation but the main bind happens at the t-case where there is no differential. On all wheel drive or all time 4 wheel drives there is some sort of differentiation at the t case.

 

[Jspafford]

To break it down a little better. When in 4WD, both the front and rear driveshafts turn at the same speed. PERIOD. Therefore the front and rear axles try and turn at the same speed. This is fine as long as you are going in a straight line, however. When you turn the vehicle. The outer tires must travel farther than the inner, on BOTH axles.

So in turn the front driveline is trying to spin at a different speed than the rear. What usually ends up happening is tire "scrub" which means one of the back tires will skid a little and then stop, skid a little, stop. Until you begin to go straight again.

In the worse case scenerio, the axles, u-joints, or in extreme cases something in the transfer case gives.

 

[ford ranger]

Thanks for the info. so the transfer case locks the front and rear together when in 4wd.

 

[AllanD]

Actually the outer tires on both axles cancel out the inboard tire turning slower.

the problem of windup comes from the fact that with ackerman steering geometry the front tires cover more distance when driving around a curve than the rear tires do.

You can demonstrate this by looking at your tracks on dirt or in snow

FULL TIME 4wd vehicles have SOME method of releasing the tension turning
generates in the drivetrain.

The AWD explorers for instance use a Viscous coupling in the
power path to the front axle.
The E4WD used in the AWD Aerostar used an open planetary differential
that can momentarily be locked by an electromagnetic clutch.

The Automatic 4x4 used in SOME '96-up Explorers also uses an
electro-magnetic clutch but until it detects rear axle wheelspin
there is NO power being directed to the front axle.

AD

 

[Bent Bolt]

Thanks for the info. so the transfer case locks the front and rear together when in 4wd.

Yup.