Difference between PDL lock and off road switch

Elaborating on what CondoCruiser said... a differential allows the wheels on either end of the axle to travel at different speeds... in a turn, your outer wheel will travel faster than the inner wheel to compensate for the difference in length it has to travel in the same amount of time.
Torque will follow the path of least resistance. In normal operation, without the PDL or diff locks engaged, if you were to lift any one of those wheels off the ground and put it in gear, you'll have one wheel spinning and you won't be going anywhere.
The power divider lock ensures that the input shaft to the #2 (front drive) and #3 (rear drive) axle rotate at the same speed. This still allows wheel slippage in the differentials (such as when making a turn).
The differential locks lock the differentials and ensure that both axle shafts continually rotate at the same speed.
In the construction industry, I've had to use those a lot. I can't recall seeing a highway truck with the diff locks, though.

 

That brings up another issue. Make sure you have all the same size tires on there. I see companies all the time changing just a couple tires with deep treads and there might be a 1/2" difference with your other almost wore out tires. Locked in they are fighting each other due to different circumferences and something has to give. Always try to get a matched set on the drive line. Stick the garbage tires on the trailer. It'll ride better too.

 

I do believe most answers here are wrong.

PDL - is the center(power divider) differential lock. This locks the differentials between the axles. It does not lock each axles differentials.

The 'off road' switch mutes the traction control so the wheels spin freely to allow the tires to clear of mud. Without the 'off road' switch in super slick conditions like mud, snow, or ice the traction control will take over so much the truck will not move or spin the tires at all.

 

You want the wheels to spin freely when you're in off-road conditions? That's news to me.

 

For those that don't know what the traction control does it uses the ABS system, brakes, and engine fuel control to modulate the traction at the wheels. As one wheel spins faster than the truck is traveling, as determined by the ABS wheel sensors, the brake is applied to that spinning wheel. That allows the wheel with traction to regain torque from differential. The engine torque is then reduced to help regain traction and prevent the drivetrain from over torquing the braked wheel.

The problem in very slick conditions, like mud under all tires, the traction control will want to brake all wheels. The stupid computer may brake all wheels, or may alternate braking between wheels so quickly that a wheel does not even make a full rotation. Power is often cut to less than idle power. Either way the truck gets stuck with the traction control trying to control the wheel spin! The 'off road' switch mutes the traction control so the wheels are alowed to spin and clean themselves of mud. Truck may move forward. Althourgh power may be cut, and at some point traction control may take over somewhat.

Axle differential lock is something totally different and unrelated.

 

Good for digging holes! Nice big holes , we can plant trucks in ! Keep them watered come early summer we can harvest new trucks .

 

I'd have to see something from the manufacturer verifying this before I took your word for it. Traction control systems transfer power to non-spinning wheels to compensate for the slippage of a spinning wheel. When you're in mud, ice, etc. you do not want a wheel spinning... the notion that this is to "throw off mud or ice" is just ridiculous, as that's a good way to overheat the tire and wear down tread, not to mention the propensity for a spinning wheel to cause a vehicle to slide in a direction you don't want it to.
Subaru uses a computer controlled differential for their AWD system to manage distribution of power between the axles, and that sounds like what you're trying to describe (albeit in a flawed way), and such a system wouldn't be compatible with a power divider lock, perhaps unless there was a management system at each differential to separately manage power distribution at each diff.. which I suppose is a possibility, but it would to prevent wheel spin, not facilitate it.

 

Just cannot believe anything that comes from a truck driver? Appreciate the respect. Read your service manual. Hell read the owners manual!

Just how do they do that? How about just like I said.

I drive truck and sometimes I do.

..

That is funny that the engineers that designed the system do not agree with you and use that phase in the owners manual and shop manual. I am going to overheat a tire in mud? Oh, man that is funny. As a driver you should know that one spinning wheel is not going to change the direction of at truck with 4 power wheels.

Really, we are talking trucks not Subaru and you know as little about them as you do trucks. Don't confuse the issue as you are confused already.

 

Not to confuse those that are already confused. But the "off road" switch may also deflate the air bags in the tag axle in a single screw set-up in addition to the features I already listed.

 

Read the owners manual !