Jake breaks in the rain

Front and rear drive axles receive 50% of power or engine braking forces each, regardless of the power divider being locked or not. The power divider (inter-axle) is essentially just a 3rd differential to account for speed differences between the 2 axles. In the event of a spinout or lockup, both axles still get 50% of the forces however, the amount of torque/engine braking force drops to the lowest common factor (the spinning or locked tire).

For example, if it only takes 50 ft-lbs to spin a single wheel, the other three wheel ends still get 50 ft-lbs each but since that small amount of torque isn't enough to move the truck, you're stuck. Now if you lock in the inter-axle, the drivetrain can utilize the additional traction available at the wheel ends of the other axle to increase the amount of torque that can be put to the ground.

 

It's good to have a mechanic in the house.

 

If I happen to be driving a truck that has BOTH a power divider (IAD Lock aka Interaxle Differential Lock) AND a Differential Lock (or separate differential locks for the front and back axle) I can definitely tell the difference between engaging ONLY the IAD versus adding the differential lock(s).

The differential lock(s) WILL make you go straight even if you want to turn. The IAD allows you to turn. Some of the trucks I have driven lately are specced for off road in Canada. They have two switches for differential locks, one for the front axle and one for the back axle. Engaging only the front axle still allows some ability to turn in tight radius turns in fracking pads while maintaining as close to maximum traction in hub deep mud and gravel.

I engage the IAD at all times in off paved road conditions. The differential lock(s) are only used when MAXIMUM straight forward traction is needed.

One if these days I need to make a video of the deep soup we have to power through to position our load (pump trailer aka 6000 hp diesel engine), sand mountains, cranes, etc. The oil companies don't always lay down a nice gravel pad, sometimes it is a deep layer of loose gravel that sucks you down if you are required to get anywhere close to a 90° jacknife. I have seen drivers snap a drive shaft in those conditions.

 

I used to always drive with my dif locked in the snow in my Pete at my last job. Had to use cross lock a lot too up in Duluth and iron range.

Anyways I haven't had to lock my dif much yet in the truck I drive now but I swear I remember it only has cross lock and yelled at me for going too fast so I turned it off.

 

My sphincter strength was once tested , it passed the test. This is a very emotionally draining test. I was lucky, I took my test about 40 years ago.

Down a mountain, ice, very light, my sphincter test went so far as to kill the engine and lock up the wheels. Crazy how fast a guy step on the clutch, throw a truck in neutral, start it, find a gear, pick up speed and steer it out of a jackknife all at the same time.

Years after my sphincter test I bought my first truck and had a very successful career as an owner operator. Just saying, us old guys with 3 million miles under our belts, didn't just wake up knowing everything.

We did have the luxury, that when we did screw up, there was not all of this traffic around us. So you young guys keep asking your questions.

 

I engage the IAD (power divider) at speeds up to highway speeds as needed. The differential locks are another matter. Don't engage those above 25 mph and only for short periods.

The OP likely does not have differential locks. Most OTR companies in the lower 48 only have a power divider (IAD) lock. The IAD will be as close as he comes to all wheel drive.

The most important thing is to PRACTICE whatever you use, to see the capabilities and limitations of your drive train system. Bobtail in an empty parking lot is a good start. Then try it again, hooked to a trailer, empty and loaded. Get a feel for what your truck will do.

 

Yeppers ....mine was about 4 years ago I 90 west in Montana around Bozeman in a snow storm... about 65000 gross weight and doing 40-45 aiming for butte for the night. Have driven that road many times east, rarely west. Did not or could not see gradual but good enough down grade, not enough to warrant a sign evidently, start to pick up speed....can only see maybe half a mile ahead.... can't slow down, icy as all get out... not sure if there is a turn approaching I will not be able to make... start eyeballing the median and consider going in there in a controlled manner or take my chances downhill... I take my chances .... the only way to keep it straight and somewhat under control is with light throttle... pass the empty bull hauler who passed me a few miles ago he may have been at 50 or 55... don't dare touch the brake... eventually road levels out and I have a few more miles to get to I think exit 298 flying j.... there was no chance in hell I was going to attempt homestake after that... that was my test and I do not wish to repeat it.

 

My brakes locked up the other day on a super greasy road doing like 50 in the rain. Scared the hell out of me because I definately didn't expect that. Wasn't really worried about hitting anything just had to see if my trailer was still behind me very quickly lol. I was totally empty. I'm used to pulling loaded tankers not 48ft vans.

My scariest moments have actually been going up hills in snow storms not sure if I would actually make it up or go sliding down backward.

 

While Jakes can be used in slick conditions, the far better option is to apply the service brakes. Better to have 18 wheels braking than 8. Jakes are another tool in the toolbox.

As you noted, sometimes it's far better to accelerate or allow the hill to increase your speed than to try to apply brakes.

Sometimes the "circle of traction" gets pretty small, and you don't want to get outside the circle.

 

If it slides because of the jake, no biggie really (on snow at least), if you are attentive and catch it the moment it happens. Just touch the throttle enough to stop the brake and when the wheels stop sliding in the forward motion apply the throttle gently enough to pull forward without additional spin added. Then it will cause the sideways slide to pull back into a straight line. All that happens rather fast, if you're to slow it's to late, then you have to do the above while adding the trailer brake to the mix in order to try to stop the trailer from passing the tractor. The last thing you want to do is hit the service brake while bent in the middle. I practiced it actually making the truck slide in the snow on the open road. Crazy, maybe, but I know what it feels like and what to do when it happens.