All depends on how heavily loaded, how steep a grade and what head of steam you've gotten built up before you try as well as how good your brakes actually are...
I spent 30+ years down that way and have never gone over I40 east from K-town heading to Raleigh w/o either seeing a rig still sitting in one of the runaway ramps or at the least very recent tracks--seems many of those guys just don't get that it's steeper coming down those "little" hills in the Smokies than it was where they came across the Rockies or Sierra-Nevadas.
This is why licensing is more stringent for big rigs. In a normal car or pickup there is a limit to the amount of collateral damage you can do, in an 80,000# semi with 150+ gal of diesel and who knows what cargo on board the potential casualties are substantially greater.
And he should be able to teach you the right way to treat them, because he's the one that sees what people do wrong. If you ride the brakes and pre-heat them, you might not even get the one full stop out of them on a steep hill.
It's all in heat buildup and transfer - You can get that one good stop out of the brakes because they were cold - but when you are done, the drums and shoes (or front discs and pads if you've got them) are pushing 500F to 700F - dull red hot to Bright red hot.
Look at today's NASCAR racing on TV, Darlington chews up brakes. Beautiful In-Car-Camera shots of glowing red rotors through the wheel spoke holes. And they already had a pileup from a driver losing the front brakes,the rears locked up, and he pirouetted and backed it into the wall HARD.
Once you release the brake pedal the drums start cooling slowly, but the shoes are now sealed up inside the drum and backing plate, and they release heat really even slower - and worse, starts radiating the heat into the hubs and wheel bearings and wheels. The tires catch on fire if the wheels get too hot, and the grease in the bearings too.
And above maybe 800F the friction materials of the shoes starts glazing over and losing it's stopping abilities.
Get them REALLY hot (I'll guess over 1000 - 1200F) and the glue bonding the lining to the shoe can fail and then you're truly screwed. But this is mostly cars that have bonded linings, trucks usually use riveted shoes.
If you can do it, ask the mechanic about converting the dump truck and/or the Semi Tractor over to Air or Air/Hydraulic Disc Brakes - they make them for all positions, but even the front axles would be a great help. It's a good sized chunk of change for the pieces, but it could easily save your life if you start running around in the mountains a lot.
"Pete C." on Sat, 03 Mar 2012 22:00:41 -0600 typed in rec.crafts.metalworking the following:
It ain't so much "brake fade" as "brake fire". And if you miss the gears on the downshift, you may not be able to get it into _any_ gear. You are now along for the ride. Google "30,000 Pounds of Bananas" for a song about what happens. "side swiped six parked cars ... and that's when he lost his head. not to mention several other body parts .."
My Dad knew the CHP who had his patrol car floored, with siren and lights wailing, and had just hit 105 miles per hour, when the truck went by him, going much faster. I don't recall if that guy made it all the way down, shiny side up. But if he did, he would not have been stopping before Bakersfield - no brakes, no luck. Now that was the old Grapevine, but the experience remains - there are not enough brakes on a truck to stop one headed downhill with a load.
2012 14:02:21 -0600 typed in rec.crafts.metalworking the following:
And then remember, "You go down a hill slow, a lot. You go down fast - once." If you are going "over a hill" (a pass) stop at the top, check brakes, load, stretch legs, then do not get in a hurry to get down the hill. Better to "creep down the hill" thinking you could shift up a gear and make it, than to arrive at the bottom wishing you hadn't, and wind up on the six o clock news.
In CT there were two fairly recent incidents of trucks loosing brakes on Avon mountain (not very big or steep really). One incident was a large dump truck the ended up plowing into cars stopped at the traffic light at the bottom killing a number of people. The second was a flatbed semi with a load of asphalt shingles, on this one the driver somehow managed to weave through traffic on the opposite side of the road, get through the intersection at the bottom, over a hundred yards of grass or so and take out the corner of a building without hitting anyone. The driver got a broken leg if I recall but that was the only injury. Last I recall they were widening the road and building a runaway truck ramp.
I don't know if they still do this but twenty years ago when I lived in the Colorado rockies there was a weigh station on I-70 at the town of Idaho Springs. They asked all the truckers who were headed west if they had ever driven over that section of highway before. From Idaho Springs it is a loooong uphill grade to the Eisenhour Tunnel and then an even loooooooonger very steep down hill grade on the other side till you get down to Silver Plume. If a trucker had not been that way before he was required to park his rig and go inside and watch a video explaining how to drive on that stretch of road and handle the grades before he was premitted to leave.
I am wondering, about those long downgrades. How do you decide which lower gear to choose? Would you pick one that would give you something like 1,500 RPM at your desired safe speed?
By the way, I found a great mobile mechanic. For just $90 and a heavy duty C clamp, he fully checked and adjusted my truck's brakes, lubricated everything, and did a lot of other maintenance and checked everything. He said that the brakes are 3/4 new, and it is generally good to drive.
I will try to get a DOT medical card, and will then take the written exam.
Experience. Really. What gear you will use all depends on what the load is, how the rig is loaded, what the road surface is, day/night, single screw/twin screw, what the grade is, what your gearing is, what items you have to slow you (Jake brake/exhaust retarder) plus some more.
The old rule of thumb is to use one gear lower than what it took you to climb the hill. IE if you made it up using 9th then drop to 8th to go down. This works IF both sides have the same grade, not usually the case. It also doesn't work well on high HP rigs since you probably used a gear much higher coming up than the ROT covers. IE: a 525 powered KW will climb a pretty steep grade.
DOT physical isn't hard. The written exam isn't hard either. The actual driving test can be interesting depending on the brownie. The usual routine for the driving test is, Show up with your driving partner (someone who has a license to drive whatever you bring and has all the paperwork) Next you will do a pre-trip and verify that everything is OK. Then it depends on their test. But you will need to do some actual road driving, paying attention to EVERYTHING. Check the gauges/mirrors/lane position/gearing (no shifting in intersections)and all the rest. Lane position is interesting because most auto drivers don't bother with it. Then you will be doing a straight line backing maneuver and parallel parking. They may ask you to do a blind side backing into a dock or something like that as well.
I would try to get as much practice in the actual vehicle you will be using for the test that you can. Driving with a trailer behind you will REALLY get your attention....
I think that I will go the route that Pete C suggested, and will rent a truck with an auto transmission, for the purposes of the skills test. Less distraction when driving and less points to be taken off, for grinding gears. I have been driving with trailers for a while.
That is why saying that "Use this gear for this hill" doesn't work. What you end up doing usually is trying to pick the gear that gives you a legal speed descent with the engine in the middle of the power band for the engine. The trick is to add all the variables up to find that gear...
Trust me driving a P/U with a trailer is NOTHING compared to a tractor trailer with a 102" wide 48-53 foot long trailer behind you. Especially if it's a bumper tow unit. Everything is different.
Both. While you could set there and calculate out the gear ratio using the weight of the vehicle, contact patch friction available, amount of available engine braking, amount of wind drag, degree of grade, and the rest and probably come up with it, folks with experience driving can look at the situation and decide, "Well for this hill 10th should do it", shift and be down the hill...
Just takes practice and knowing what your rig will do with the given load. Most of the time a good driver will have an idea about how the load will handle after about the first mile or so pulling it. Just in the way it feels through the wheel and the way you shift to get moving. Every load will act different depending on overall weight, center mass, center of gravity, wheel spacing, number of drive axles 5th wheel location, road conditions even the wind resistance and drag under the trailer all make profound differences.
Now add in people tailgating, cutting you off, erratic speeds, long hours, and all the rest and it gets a bit stressful in that rockin' chair. It's one of the reasons there is a shortfall of drivers out there.