mowermech
Billings, MT
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Joined: 06/28/2003
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Generally speaking, (and, as with ALL generalizations, yes, there ARE exceptions), you will want to use the same gear going down the hill as you would use going up the hill.
CM1, USN (RET)
'94 Dodge 3500 4X2 CTD, 5 speed, 4.10 LS diff., Jacobs Rambrake, 274,000 Miles
'99 Monaco McKenzie 32' triple slide
'95 Tioga 29H Ford-based Class C
Daily driver: '08 Subaru Outback
Towed: '06 Jeep Rubicon Unlimited/Load Trail 16' flatbed
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miltvill
Ft. Lauderdale FL
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GM uses the Allison Transmission to slow down the Duramax diesel. Look in your owners manual under towing. It may provide info on your transmission.
2008 Chevy 2500HD Duramax Diesel, Allison Transmission, 3.73 rear end, tow package, Prodigy Brake Controller, Equal-i-zer Hitch.
Trail Cruiser TC23QB
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BurbMan
Long Island, NY
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Joined: 09/20/2001
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In most trucks with 4 speed OD transmissions, selecting 2 will keep you at or under 55 mph without using the brakes. Manually selecting the gear on an auto tranny should also lock out the auto-upshift at redline. First gear will keep you under 30 mph or so. These are general guidelines, use them accordingly. Pay attention to transmission temps when using the tranny for grade braking, it will heat up some. As was noted, get into a lower gear at the top of the hill before you start gaining speed. If the road is straight and you have room to accelerate before it flattens out, you can upshift easier then downshifting.
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jrstout89
Tehachapi, Ca
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Joined: 10/13/2009
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Thanks for the info. I'm sure I'll have more questions later. Truck will be coming with the 5 speed Torqueshift which I hear good things about. I live @ 4000ft and going down to Bakersfield brings me down to about sea level. Pretty good grade to test out the rig.
Thanks again.
2010 Ford F250HD V10
2010 Jayco 30.5RLS
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carringb
Corvallis, OR
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The torqueshift will automatically downshift when Tow/haul is engaged. This will downshift 1 or 2 gears depending on brake pedal effort, and will also downshift if cruise control is set.
Bryan
2000 Ford E350 DRW Wagon (14-pass all captains chairs)
V10 w/ Banks PowerPack, Diablo Predator, 4.56 LS, 250,000+ miles
Had: Weekend Warrior 41' FSW
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smkettner
Southern California
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Joined: 03/21/2005
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Tehachapi down to Bakersfield is not that difficult so it will make for a good trial run.
2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
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BenK
SF BayArea
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Joined: 04/18/2002
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Ah, Tehachapi...know it well. Designed and installed lots of windgenerators up
there in the Arbutus Wind Park (is it still named that?). Where I almost
killed myself and 2 workers going down to that parks entrance. Loaded my
dads Siliverado C10 (now mine, see sig) and lost all braking from the TV
and Utility trailer (double axle with electric brakes on all four
wheels). Does the Air Force guys still fly through the pass upside down?
Tough road towing heavy in either direction.
Gassers are throttled, so when idling down, they have lots of engine friction
(it is really just an air pump). Diesels are not throttled and are
wide open, even at idle (speed is regulated by the amounts of fuel
injected).
So gasser engine braking is just trying to spin it faster and the
subsequent friction and losses.
Tough on the whole drive train. Not much different than hitting the
throttle hard to accelerate.
Diff gearing is the first thing this sees. The lower (higher numeric)
it is, the better for engine braking, as it will try to spin the drive
shaft faster.
Next is the tranny. You say auto, so there is fluid coupling and the
slippage that comes with it. Guess lock up (where there is a mechanical
dog to lock out the hydraulic coupling) isn't initiated (only a guess).
Again, the lower the gearing (higher numeric ratio, with 1st being the
lowest) will 'try' to spin the engine faster.
Like others have said, todays automatics have computer controllers
which will try to protect it and the engine from over rev'ing. So trying
to get it into a lower gear *AFTER* you get to a very high RPM, might
find that the computer won't allow you to.
Key is to NOT allow it to get too high in the first place.
Brake hard enough to scrub off speed to go below where you want, say
50 MPH. Brake down to around 40-45 MPH, then make sure it is in a low
enough gear. Allow it to build up to, say 55MPH, then brake again.
All the while keep the tranny in a low gear, but not so low as to
over spin the engine.
Why the TOW/HAUL function was invented. For those who don't know HOW2
manage towing and especially for going up/down hills.
Since a fluid coupled tranny, make sure to have ATF (auto trans fluid)
in good shape. I flush all 16 quarts every other year and somethings
right after a tough tow. ATF is sheared between the vanes inside the
auto tranny's TC (torque converter). That is where most of the heat
is generated.
You will hear 'stall' point and is when the fluid stops shearing and
behaves as a solid to the TC (there will always be some slippage {shearing}
but less when the stall speed is reached. This is when there is the
greatest engine braking is. Since still some shearing going on, the
ATF will heat up on long grades braking the whole setup.
Make sure you have an external ATF cooler. If not, install one. Not
hard and the instructions on most kits I've seen good for most back
yard wrenchers.
After that incident at Arbutus, I always carry an extra set of trailer
brakes. Also adjust them or check them at every stop. Lost all braking
coming down Arbutus to the highway. Cooled them down and then had them
repeat the whole experience going down to Bakersfield....even though
had tossed out several gear boxes to lighten the load
-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...
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Dave H M
IL
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It would be interesting to know the per cent of graade and if it is interstate or state mountain roads. I never sownshift going thru the Smokies on the interstate on the 6 % grades - don't have to.
Also I run an old power stroke without an exhaust brake.
And I only have to use the brakes lightly occasionally.
Also I changed the factory pads at 120 some K.
So without knowing the grades and curves, maybe you have a non issue m
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coolbreeze01
Redding, Ca
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Joined: 08/24/2006
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The OP lives on a hill. Possibly higher and steeper than you see back east. With a little driving, he can get into some really steep country 
2008 Dodge 3500 CTD LB SRW 4X4 6-Speed Auto
P3 Blue Ox Sway Pro
2007 Komfort 212
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TheRealDoug
Chattanooga, TN
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Joined: 03/10/2009
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othertonka wrote:Here is a suggestion to figure out which gear you should be in going down a hill. Take a piece of paper and pencil to record your findings.
#1 Determine your red line by looking in your owners manual, say for example it is 4500 RPM's. You need to get some baseline readings and that is what we are doing
#2 put your truck in first gear and accelerate until you reach 4300 RPM's, record the MPH's, In my case on a chev 8.1 with a 5 speed allison, it is 25 MPH at 4200 RPM's
#3 shift into 2nd gear and take it up to 4300 RPM's and record the MPH, in my case it is about 45 MPH at 4200 RPM's.
#4, put it in 3rd gear and do the same, up to 4300 RPM's and record your MPH, in my case it is 56 MPH at 4200 RPM's Now yours will be different depending on what tranny you have, I have a 5 speed allison, yours will be diffferent but the method is the same. Now make your self a DYMO lable with these figures and place it on your dash. Now when going down a hill, you can look at your speed, and if it is say below what your reading for 1st gear is, that you should be in 1st gear. In my case if I am coming down a 10 % grade and I want to keep it below 25 MPH, I down shift to 1 st gear at the top of the hill and when the RPM's reach 4200, I hit the brakes and bring the rpm's down to about 3500 and then release the brakes and let the RPM's climb again to 4200 and do the whole braking processs again, Use the same method for all other gears, this is will keep form overheating the brakes as they will cool when you let off for a while. If I am going between 25 and 45, I shift to 2nd, between 45 and below 56, I down shift to 3rd. By having the figures right on the dash, I know if I am below, say 56, I can safely down shift to 3rd without overreving the engine. Most modern transmissions will not let the downshift take place if it will end up overreving the engine, but with my method, I manually take control of the downshifts knowing in my mind I will not be overreving with my downshift.
any electronically controlled transmission will not allow you to downshift into a mechanically overrev condition. I've tested this by manually downshifting into 1st while doing 45MPH. The computer won't let it happen.
-d.o.u.g-
I've got one in the chamber
and two in the clip; doing
what I can to die on my feet.
08 CrewCab 4wd Frontier
My dad's Sir Edmond Hillary tent
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