The descending rule of using the same gear to descend a grade as you used for climbing the grade no longer applys as the the newer diesel have so much more power so they climb faster than in the past, however the downside grade can/will be slower. Cabbage Hill is this type of grade. Upside is 60mph easy with a downside of 25mph.
Watch for the "truck" grade speed limit signs and use them as a guide line. Those signs account for the slowest curve on the down grade. Colorado is one such place this really apply's too as the speed limit will be 35mph(for cars) then they throw in a 15mph 180º hairpin corner that can really smoke the brakes quickly.
Cabbage Hill on I-84 just east of Pendleton,Or. is another example as this ain't no hill but a serious grade. Tons of truck speed limit signs for 25mph but 90% of the grade can be run at 40mph to 50mph then the last curve is a 25mph 120º left hand curve and drops to 8%. Any day of the week at any hour day or night, you will see truckers at the bottom with fire extinquisher putting out tire and brake fires.
After forty years of driving mountains, the best advice I can give is if you have to use your brakes more than 3 times descending a grade then your in too high of a gear and need to use the next lowest gear. While in the correct gear then you may have to touch your brakes maybe once or twice to control maximum RPM.
If you miss judge a grade for the correct gear for a given speed, imeaditly slow down by first aggressivily manualy applying your trailer brakes then lightly applying yout TV brakes and when you reach the correct redline RPM then downshift shift to the next lowest gear. If you don't then it will only get worse the deeper you get into the grade. Correct your mistakes early.
Remember it's much easier to up shift to gain speed than it is too loose speed and down shift. Always error on the slow side.
I found that a diesel engine has good compression braking at near redline RPM. Example: my PSD redlines at 3400rpm so I use 3000rpm to 3400rpm to descend grades. If needed I brake semi aggressivly from 3400rpm to 3000rpm usually with manualy applying my trailer brakes and lightly applying my TV brakes then let the speed climb back to 3400rpm before touching the brakes again. This lets the brakes cool between braking.
I pull my flatbed trailers fully loaded, about 28kGCW, and I get 75k to 100k miles out of my brakes and rotors using the above method. A exhaust brake is not needed with the correct driving style.
T_Bone
02 F350, 4x6, Crew, DRW, PSD, 6spd, 3:73, LWB
32ft RKSS Serria
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On the commercial side of things (or anyone with a manual tranny should adhere to the same advice) you should NEVER EVER attempt a downshift once you start descending a grade.
For commercial trucks it's difficult to almost impossible to actually accomplish the downshift due to the unsynchronized nature of the transmissions - if you attempt to downshift anyways and you don't have the RPM overhead necessary to match road speed to transmission speed (not to mention the ever increasing speed while attempting the shift unless you can manage three pedals at once to maintain the brake application) you will only end up spinning into neutral, and then your in serious trouble.
For RV TV's with standard transmissions I'd still not recommend it as road speed can quickly spiral out of control as soon as you clutch it and try to donwshift.
For automatic transmissions you could probably get away with it nowadays, although one must remember that if you are at redline in third descending a grade and you select second, the transmission will not complete the downshift until it can do so safetly...meaning without a heavy brake application to reduce speed, it may be fruitless.
This is the reason the cardinal rule is to select your intended gear at the top of a grade, and stick with it. Even attempting an upshift on anything short of an automatic can result in a very bad situation.
Quote: ...On the commercial side of things (or anyone with a manual tranny should adhere to the same advice) you should NEVER EVER attempt a downshift once you start descending a grade.
I'll disagree with your blanket statement of never to down shift.
I'm gonna take a short cut from NV266 to CA168 heading too N.CA395. I'm 48ft overall at 16kGCW using my ole Dodge 4wd,4spd-m. As I top the bluff and on the DOWN side, comes a warning sign of no trailers over 20ft and no grade warning but you can see the 8 mile bottom and the roadway is anything but straight(as the map shows).
Now the signage is over the top and even if had it been on top, there's no place to turn around, and a couple hours or so to do a 4pt 180º. A 4pt 180º is where you disconnet the trailer and manual walk it in the opposite direction. Not fun at all but it can be done.
A quick gut decision said to go low, very low and right now. I hit the trailer brakes at maximum, lock the TV brakes and I'm in serrious trouble, so I jabb the ER brake hard at which point the ER brake cable snapped. Another 100ft and I'm stopped. Think GOD as I was just about ready to put my rig into the rock wall on the right side.
2nd gear and low range put me at about 10mph at just under confortable maximum RPM. In this geared mode, I will have to add fuel to move forward on the short down flats.
My gut feeling was right on. The 12% grade was nothing but slow tight switch backs the entire 8miles where I used both lanes on the corners.
Had I not stopped to gear down, I would not be writting this now.
klutchdust wrote: Big rig drivers use the rule that you go down a hill as fast as you could go up it, now do they follow it? Stay off the brakes, don't ride them, once they overheat they are useless. Be safe.
This has some very important information especially if you are in mountains that you are not familiar with. Going up a hill see what the speed of the Big Rigs are and when going down start out really slow and DON'T pass the slowest Big Rig who probably knows how bad the downside is. Here is one instance when decending a serious grade less (speed and in a low gear) is much better than using too much brakes. I also use the shorter, harder breaking to get the speed down even lower than I actually want to decend the hill at and let it gradually speed up. Doing this and going down a serious grade at 35 or 40 mph in a low gear is much more recoverable than trying to scream down the hill at 55/60 mph and only using your brakes. Just stay in the far right lane and turn on your 4-ways when under about 40mph.
Larry
2001 standard box 7.3L E-350 PSD Van with 4.10 rear and 2007 Holiday Rambler Aluma-Lite 8306S Been RV'ing since 1974. TRAILER MODS
T_Bone wrote: I'll disagree with your blanket statement of never to down shift.
I'm gonna take a short cut from NV266 to CA168 heading too N.CA395. I'm 48ft overall at 16kGCW using my ole Dodge 4wd,4spd-m. As I top the bluff and on the DOWN side, comes a warning sign of no trailers over 20ft and no grade warning but you can see the 8 mile bottom and the roadway is anything but straight(as the map shows).
If you can STOP before downshifting, then that's a a different story, but when that becomes impossible the cardinal rule still stands as I explained it - never attempt a downshift.
And as I mentioned, this rule changes a bit if you have an automatic transmission as there's no risk of accidentally ending up in neutral as is possible with a non-auto...but even then it's still a risky maneuver.
BTW, part of being a wise traveller is always knowing what the road ahead is going to offer up. I've never been caught off guard by a mountain pass or large grade simply because I spend some time at the start of every day looking over my maps and planning my route accordingly. As a commercial driver (my viewpoint) coming upon a grade that I couldn't descend would be no different from a problem standpoint then coming upon a bridge that I couldn't get under, so planning makes all the difference.
The only thing I can emphasis on all of the previous posts is to watch the truck warning signs and the behavior of trucks. If you are not familiar with the down grade do what the slowest truck is doing. Other posters have said that "you can only go down a hill too fast once, but many times too slow". No trucker or RVer will be critical of your slow descent, the've been there and understand.
Here is a easy way to find out. With somone to write down the results, get on the freeway or a 55 MPH highway and go about 3/4 throttle. Then call out the upshift speeds, and write them down.
Lets say that the upshifts are 25, 38, 48, and 55 MPH for the lower 4 gears.
Then you will know that you can shift into 4th at 55 when going over the top of a hill, for maximum braking effect, and can shift to 3rd (in your 6 speed automatic Dodge truck) at around 48 MPG.
Your speeds might be much less, so be sure to check them. With a governed RPM on your engine being fairly low, the speeds might only be 18, 30, 42, and 55. The top overdrives should only be used when the engine does not need to make a lot of HP to get the load down the road. So even a slight upgrade and headwind might require driving in 5th gear to make enough power to keep the speed stabil.
Fred.
Money can't buy happiness but somehow it's more comfortable to cry in a Porsche or Country Coach!
Another item they should find out is what speed is produced at maximum RPM or redline RPM in each lower gear. Most of the newer diesels are goveren upon accelleration but can exceed redline RPM upon manual down shift.
I would bet also that most gasser's are the same way since they are also a DBW system.
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