Front (Steer) Drive Axle

You can make a vehicle All Wheel Drive (AWD) by utilizing a driving front axle powered by a transfer case. The transfer case will have a drive shaft to the steer axle. This aids with traction in off-road applications at speeds under 35 mph. The cab will be raised from the normal build position to gain clearance for the additional drivetrain equipment.

The transfer case takes some special consideration. One aspect that you should be aware of is the ratio mismatch with the rear drive axle/s. It is uncommon to have the same manufacturer supply all components, and the designs do not allow for matching ratios. As such there must be some compensation to align the front and rear tire revolutions within a given tolerance.

Select ratios for the front and rear that are as close as possible. Then fine tune the combination by making changes to the tires. Its is the Static Loaded Radius (SLR) and Revs Per Mile (RPM) that are considered, with engineering preferring SLR as a more accurate assessment of how the vehicle will operate. When the OE performs the calculation, they are looking for a maximum of 1.5% difference between the tire revs.

As tires wear, they decrease in size and SLR while increasing in RPM. This will impact the difference and should be accounted for. Additionally, when tires are replaced, the replacement tires must maintain the same SLR and RPM as the original. Transfer case gearing can be damaged when this is not adhered to.

Too much of a risk for your customer? Consider the EZ Trac hydraulically driven steer axle. This is an aftermarket swap that retains cab height, eliminates the transfer case, and allows for programing of speed to compensate for tire size differences.

And now…

---

Believe It OR Not

If you were to spell out numbers, how far would you have to go until you would find the letter “A”? One thousand.