Downhills!

This will depend on the engine, but most will tach 2100 safely.

BUT !! Many companies track over revs. And, many companies call anything over 1800 an over rev.

The new twin turbo cats will safely rev to 2000 rpm. At that point you need to grab some brake. I generally try to get in a gear that can hold the truck at about 17-1800 rpm.

 

This is true...there are MANY variables here. Depends on what engine you have, transmission, jake brake, and other things. For example, I had a 460HP Cummins and I would keep the jake on full, the tach at 2100 and RARELY ever had to touch my brakes no matter how long the hill or how much weight I had on.

 

I was taught (this was many years ago and still holds true today) that after you have selected the proper gear for down-hill (same gear or one lower than you climbed the hill with) you apply 10-15lbs of air pressure to the brakes and that should hold your speed without over-heating your brakes. If you do not have an "Air Application Gauge" on your dash, 10 - 15lbs is just enough brake to "feel" the drag and no more. The TROLLY Bar comes in handy for this.

Also; you can "stab" the brakes every 15 to 20 seconds and achieve the same effect.

If you have "over-cooked" your brakes, one mistake I see many drivers make is to stop at the bottom of the hill and apply the brakes and wait for them to cool. This allows heat transfer from the drums to the pads and may further damage the linings. If you MUST stop, apply the brakes, chock the wheels to prevent the truck from rolling, then release the brakes.

I saw a Swift truck with over-cooked brakes on the northside of the Grapevine set his brakes at the TA. The tires heated so much from red-hot drums that it blew two tires simultaneously. I was standing 25 feet away and was almost knocked over.

 

:smt043

 

Mack, I dunno how to do it because I haven't been to school yet, but I'm studying for my permit test and that's exactly how it says to do it, so I guess it does prove reliable in the real world....good to know.

 

Don't forget to keep slappin' your cowboy hat on the side of your seat & dig them spurs in every so often.

Oh & a good strong YEEEHAAAAWWW as you hit the grade ought to do it.

 

Lemme throw somethin' in that hasn't been mentioned yet.
Many hills will have a posted truck speed limit for falling off them.
Some, like in Cali, have a 35 mph max speed.
Others, like MontEagle, have a different speed limit but less than the 4 wheeler limit.

How you fall off the hill is dependent on a number of factors as each responder has provided.

There's a couple schools of thought on braking. One is stab breaking & the other is the long drag (my terminology). Each has its good & bad points depending on the situation.

I think you understand the long drag is not much more than applying 5-10 lbs of air pressure for a good part of the downhill.

This assumes you have properly adjusted your brakes before falling off the hill. The better matched your brakes are, the more evenly the braking load is distributed amongst each axle. This equates to slower heating because each brake is doing its fair share of the work.

Depending on your weight, the grade & speed you might even need to release the brakes every so often to keep your speed up. Or, for the same reasons, you might need to momentarily add some braking to bring you back to a safe speed.

Despite the best brake adjustment & minimal air pressure, it will take awhile but the brakes do eventually heat up & you may not have much leftover before the bottom.

The trick is to "know" the right speed that allows you to apply minimal braking to keep at that certain speed for the duration of the descent.

Next is the stab braking routine. Like it sounds, that's what you're doing. You fall off the hill at a slow enough speed that allows you to apply a fair amount of pressure for short periods that bring you back to the speed you want to be at. Usually you won't let your speed get more than about 5-10mph more than you want to run & then hit the brakes for a few seconds to slow back down.

Again, the trick is in knowing how slowly to fall off the hill so that by the time you've bottomed, you haven't overheated the brakes to the point of "aww crap".

All of the above assumes no Jake brake.
Even without a Jake brake, your motor will offer some braking action.
You just need to figure out which gear to be in that makes either braking procedure easier on the truck/trailer.

The "knowing" is admittedly the hard part. It comes from experience & watching what others do. Heed the speed limit signs. You also have to be familiar with your truck & trailer & the limitations for each.

I've used both procedures coming down the hills all over the country & Canada & had situations where one way was a bit smarter than the other. I haven't "smoked" a set of shoes yet. My typical gross is always in the 79,900 range. (Food grade smooth bore tanker)

There's a third thought that someone mentioned.
It is using the trolley brake.
There's merit in this under certain circumstances.

Snow & ice not withstanding, if the hill isn't too bad you can use the trailer brakes & keep you tractor brakes in reserve. However, this does work the trailer brakes pretty hard & they will get warmer quicker than if you used all the brakes available.

As a wiser person than me once said, "You can fall off a hill too slow a thousand times. You only get to do it too fast just once."

 

First; Why would you publicly advocate speeding down a mountain when answering a newbies question? Monteagle is speed restricted at 45 mph for trucks.

Second; Monteagle is a 5-6% grade.

Third; If a driver with an 80,000 gross weight were to jump off of an 8% grade at 50-55 mph by time they got to the bottom, one of two things will have happened. Either they will have spilled it and be dead or they would be on fire.

For example; Cabbage (I-84 in Oregon) is 6% for 6 miles. The posted truck speed for 80,000 pounds is 18 mph. Would you jump off of that at 55? And yes, I know that 18 mph is ridiculously slow, but wouldn't suggest falling off at more than 30-35 mph.