Hills/mountain descending?

I come off of Verde SB at 75K+ and Parley at 35 to 40 mph Jake on at about 1800 rpm flashing my 4 ways and don't worry a bit about getting passed by some guy hauling ping pong balls or toilet paper.
Years ago in a cabover I guessed wrong where I was on Mountain Pass NB I 15 Cali/Nv border and some hill in Nevada on 80, had to throw it out of gear to not way over speed the engine when I saw it was finally straight road and ran into the triple digits...won't ever do that again.

You can go down a hill too slow every time...too fast just once.

 

Not trying to start an argument here, but the lines I bolded in your above post are not exactly correct.
Inter axle locks are often a "cloudy subject" for many/most tractor trailer drivers. Many misconceptions all around.

However, it is definitely not required to stop the tractor to engage of disengage an inter axle lock, commonly misnomered a "differential lock" by many.
What is vitally important is that it should NEVER be switched when any wheel has lost traction and is spinning.

Here is a real life scenario, when it especially must be engaged while the truck is at road speed.
If you were to be climbing a grade and begin to lose traction (typically begin to run into icing or slick spots on roadway), it would be significantly proper and vitally important to let off the fuel momentarily to assure no tire slippage, and immediately engage your inter axle lock to provide the required traction for the grade and conditions.

If you attempted to stop on the grade to engage the lock, you can just imagine all the safety hazards this would create, not to mention it is likely to be impossible to even regain traction from a dead stop, to even move the vehicle up the grade, locked or not.

I personally have had to engage an inter axle lock many times at speeds greater than 25 mph on grades/hills.

I've also driven trucks where the factory switchplate for the inter lock switch specifically says:
"Shift At Any Speed Except If A Wheel Is Spinning". This was the manufacturer's text on the switchplate, verbatim.

From Roadranger manual, excerpt as follows:

Use lockout when approaching: ice, snow, mud, wet surfaces, or loose terrain.

Lockout Operation
1. Temporarily release the accelerator pedal. This interrupts the torque
applied to the inter-axle differential allowing easy engagement or disengagement
at any speed.

2. Flip the lockout selector valve to lock (engage) or unlock (disengage)
the lockout.

Remember:
• Engage lockout at any speed with accelerator released. Never
engage lockout when wheels are slipping.
• Use only under poor traction. Do not operate truck with lockout
“engaged” on dry pavement.

That said, now Eaton/Dana states it a bit different, an excerpt from their manual:

The Dana Drive Axle Wheel Differential Lock is an air-actuated clutch which
positively locks the differential gearing in the rear axle. When this clutch is
engaged, power flows to the tires without any differential action, giving each
wheel all the torque the road conditions will permit.

The Wheel Differential Lock is engaged by a cab-mounted valve, causing the
clutch to move in or out of engagement. This motion also trips an electrical
switch used to activate a light in the cab or sound an audible device, indicating
that the Wheel Differential Lock is engaged.

WARNING: Do NOT use your Wheel Differential Lock when traveling
downhill

WARNING: Do NOT use your Wheel Differential Lock at speeds over
25 mph

Engage
1. Flip the control lever to the “Lock” position, either while the vehicle
is stationary, or while moving at a steady speed under 25 miles per
hour without the wheels slipping (spin out).
2. Let up momentarily on the accelerator pedal to relieve torque on the
gearing and fully engage the clutch.
3. When the differential lock is engaged, the indicator light will be on, or
an audible signal will sound.
4. When the differential lock is engaged, the vehicle will understeer,
requiring a longer turning radius for a given turn.

Disengage
1. To disengage the Wheel Differential Lock, flip the control lever to
“Unlock”.
2. Let up momentarily on the accelerator pedal to relieve torque and
allow the clutch to disengage.
3. When the differential lock is disengaged, the indicator light and/or
audible signal will go out.
WARNING: Engage Wheel Differential Lock ONLY when vehicle is
stationary, or moving without wheel slippage.

Important To Remember
When engaged, the Wheel Differential Lock will cause the vehicle to understeer,
meaning that the vehicle will not turn as quickly, and more steering
effort will be required.
Use your Wheel Differential Lock only at speeds less than 25 miles per
hour; at higher speeds, the understeer handling characteristics could be
dangerous.
The differential lock should be engaged only when the vehicle is stationary,
or moving without wheel slippage (spin out).
This system should only be used when poor traction is encountered; it
should be disengaged under normal traction conditions.

Actually, unless there is a difference between the diameter of the front drive axle tires and the rear axle drive tires, engaging or disengaging the inter axle lock at any speed will do no harm, as both axles will be turning at identical speed (rpm). But the NEED to disengage or engage it above 25 mph is limited to very few occasions.

 

So who reads the directions? Thx, KW!!

 

It's a "guy" thing.... no guys read directions!
Actually, I don't trust all that I read, at any 100% level.
But if what I read matches my known understanding of the actual operating "mechanicals" of the machine, then I can say it's understood.
If I don't understand & can't verify, oh well... then I keep digging for info to fully understand its operation.

 

Good post KWCajun. Most of the time when starting up a grade or leaving the Pavement I throw a switch instead of waiting till I lose traction. Just like grabbing a gear. Clutch the Interlock and Lockers. When you get into the corners clutch out the front Locker till ya straight out then reengage. When it's all said and done I stop and back up 20-30 feet to disengage any accessory drives that might still be engaged. PS-Real drivers wear boots not tennis shoes.

 

Pointy boots, big belt buckles and funny, big sun hats?

 

5% grade generally will be 9th with the engine brake unless it's really long. 6% would suggest 8th unless it's short distance. 7% 8th gear with engine brake. Could go down to 7th on an 8%. Just take it slower at a lower gear the first time down a hill. Once you're familiar with it you can do it a bit faster the next time

 

Um no. Those are flat landers. Steel toed boots,Carhart coats and hard hats. And the Tire chains hanging on our trucks are shinny.

 

Do they make those steel toes in a flip flop and does Carhart make sweats with a stretch waistband? This is the reefer forum in case you missed it.

 

Back to pointy boots...