newbie questions about descending grades and gears

yep stick with the old skool method of going down the hill one gear lower than the gear you used to go up the hill. then after you get more experience you can start selecting a different gear.

 

PMSL, I luv this comment, good onya, there r some bad/dangerous drivers out there and they need a little reminder every now and then.

 

I drop down a gear or two as I'm cresting the hill and getting ready to start down. Better to do it up there while you can instead of screaming down the hill when it's too late. Oh and put your flashers on so ppl know you're a slow moving vehicle.

 

What happens if its a 1 percent grade going up and a 6 or 7 going down.That one gear lower doesnt work.Heres how its done,and Ive used the snub method and this method Im about to describe.On 8 or 10 speed trucks,High gear low range.Constant 5 to 10 lbs of pressure on the brakes.The key here is constant pressure.If you allow air to get in between the linings with this method your in trouble.Try this as an example.Take your hands and put them together palm to palm.Now rub them together with pressure as fast as you can.They get hot pretty quick.Now do the same thing at a very slow speed,barely moving,you could do this all day and they will never get warm.thats the principle.It works.Trained new drivers on this method w/out a jake on ever major pass in the country at over 65000 lbs,and the brakes have never even been remotely hot.Sure your only moving 15 miles per hr,but thats how its done.Use to train new drivers on the snub method and had to many problems with it.Crystalized brakes,hot hubs,brake fade,etc.Everybody chime in,im sure Ill get some discussion on this.But it works if you dont have a jake.And our drivers are trained on proper descent of mountains w/out a jake.

 

There is a large sign giving recommended speeds according to gross weight right at the end of the brake check area. Offhand I think it says 25mph for 80k, but I could wrong, it might be lower.

I would want to be in my descent gear while on the flat, before the downgrade starts, right at the end of the brake check area.

With no jakes and a full load, I would probably start the downhill in 5th. The reason being that if I have to downshift more I won't have to deal with the range shifter. In general downshifts are harder to make than upshifts.

In my experience it follows the torque curve of the engine, increasing effect until about 1400 rpm and less effect as the rpms increase.

What I would do is go no higher than 1500, so that I could get another downshift in if I had to, OTOH if i felt that I was keeping good control of speed with limited braking I would let it go higher, but not above redline (2200 in my truck) The key is being in control.

I think about a 25% duty cycle works. What I feel for is an increase in brake pressure or time to bring the truck back to control speed. If control is sliding away from me it's time to drop a gear.

I know that mountain driving worries drivers, but from my experience, the 50 miles of flat, level, straight, well maintained section of I -5 from Eugene to Salem is the most dangerous section of road I travel.

 

Well, I will disagree slightly with the one gear lower than you crested the summit people.
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First, when I scale the load, I balance the load between the drive tandems and the trailer tandems. My formula is take the trailer tandem weight and subtract the drive tandem weight. Then divide by 500. The answer is how many holes do I INCREASE the trailer wheelbase. NOTE: If the answer is a negative number [drives are heavier than trailer tandems] shorten the trailer wheelbase that number of holes.
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A very good idea is to pull over and stop at the top of the grade and check your brakes. Insure that the brakes are properly adjusted before you attempt to descend.
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Next, pick the maximum speed that you want to descend the grade. Call this your personal safe speed. The highest safe speed you should possibly use is the posted truck speed limit. You can always pick a safe speed that is lower than the posted truck speed limit.
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Select the proper gear for the safe speed that you have selected. Start down the grade S- L- O- W- L -Y and upshift until you get in the proper gear for your safe speed.
.For example: if the posted truck speed limit is 25 and your transmission is a straight 10 speed, the highest possible gear that I would ever use is 7th [2+5]. Most likely I would choose 6th gear and have the Jake brake on full/high.
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For the proper braking technique use the following Snub braking technique :
.When you reach your safe speed, apply the brakes firmly so that you reduce your speed to 5 mph less than your safe speed in about 15 seconds. Then release your brakes. Repeat as necessary.
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When I say apply the brakes firmly, this is more brake pressure than light steady braking and less than an emergency braking like stab or controlled braking. While reducing your speed 5 mph in 15 seconds sounds like a panic stop, it really is not.
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Light steady pressure is not currently the accepted proper braking technique because it does not ensure that all the brakes are activated. Additionally, thermal imaging has shown that light steady braking creates higher braking temperatures than snub braking. The old drivers don't believe it but the testing proves snub braking is superior to light steady pressure braking. That is why snub braking is the only accepted braking technique for use on steep or long desends in the current CDL Driver's Manual.

 

One thing I have not seen mentioned is as you crest the top...let off the throttle and begin the decent without power...in gear of course but not "launching" off the top. Once you experience the rate of decent you can get a better "feel" for what gear will keep you in control without excessive braking.

 

The current CDL drivers manual written by goverment officials,lol.Constant pressure at 5 to 10 lbs at 15 mph works.We train drivers on this method everday.Nrver so much as a hint of heat on the brakes.Where as the snub method for an inexperienced driver is much harder to learn.And more prone to heating your brakes.Ive seen many drivers smoking at the bottom,or pulled over to let brakes cool as we tortoise by at 15 mph we no brake fade brake smell or crystallization of brakes.To each his own I quess.

 

Simple physics my man.If you have a fire and add oxygen what do u get.You get a bigger fire.Same thing here.You add air to heat you get more heat.Donner pass is a different kind of pass,To long to use this method.Lets say cabbage.Steady descent for 6 miles.Now try my example that I mentioned in my explanation on friction.Put palms together and rub very slowly.You could do this all day with very little heat generated and very little discomfort.Now do the same thing very quickly.Heat builds quickly and becomes uncomfortable very quickly.Same principle.We teach it everyday with great results.The same principle applies to your brake linings.Did you not take science in school.lol,sorry just had to throw a little jab in there.