Raise my tumbler to grade braking....

[cdlaine]

Not exactly sure of the "how" it works but do enjoy the result. This past weekend had the pleasure of driving a few 6% grade declines on I-17 between Flagstaff and Phoenix. Some moderate twisty - winding curves included and an intermittent gusting tail wind. Using grade braking with just the occasional truck/trailer brake assist was really able to feel "in-control" at all times.

Much verbage is spent here on the getting up-the-hill aspect, seems the downhill performance is under appreciated. I know, no big deal, but, just wanted to tip the cap to the engineers that married the Allison to grade braking. Tranny temp gauge never budged.... checked all hubs, wheels, tires for signs of heat...none. Also, no aroma from the cab or brakes.

Often we complain about the little things .... TV performance on grade declines is one of the big things we rarely hear many cheers about. I've never experienced a "jake brake" but if anything like what I have now you owners must be well pleased.

What sayeth the platoon ?

One of my mentors use to drill into me... "they pay us for the landing not the take-off."

Charles

2003 Silverado 8.1L (496 cid), 4.1 rear end, Allison trans.

2013 Arctic Fox 29 5T, Silver Fox Edition, CAT scale (loaded) 12,600.

[GeorgiaHybrid]

I use the Jake brakes on my little truck all of the time. I sometimes have to give it some throttle coming down a grade or switch it to the low side of the Jake to keep up my speed.

[mptjelgin]

I towed with a 1999 Ford F-250 V-10 truck for 10 years, and then bought a 2010 Ford f-350 V-10 and have used it for the past 6 years. By far the greatest difference is the Torqshift transmission with the tow/haul mode which includes "grade braking" as you describe it. On long downhill grades with my heavy fifth wheel I seldom touch the service brakes at all. The torque converter stays locked and the transmission downshifts as necessary to hold speed on those grades. It is a little odd at first to see the engine spinning 4000+ rpm but it generates an enormous amount of compression braking. Even when approaching stop lights at the first touch of the brake pedal the transmission downshifts and assists with braking. Truly a great improvement...

[cdlaine]

Hybrid....

 

Nice rig. Looks like you didn't bring a pocket-knife to a gunfight. Just for clarification... is a

"jake brake" tied in to the exhaust ? Do you have to activate it or is it full-time or on the fly ?

 

Mark..with my rig... cruising speed / towing rpm lives at 2200. 6% incline hovers around 4000 rpm,

6 % decline with activated tow haul grade braking at about 55 mph... locks in around 3000 rpm. To be honest,

I haven't mastered the braking at that first stop light after grade braking... occasionally triggers the dreaded

wife-comment/correction response scenario. Apparently, I am still "a work in progress". but, I'm sure

I'm the only one here with that status.

 

Charles

[trailertraveler]

Charles,

 

If you liked your truck on I-17's grades, wait until you do something like US-191 South into Vernal, UT with 8% grades and 10 switchbacks in 9 miles. It is an awesome advantage. I have a 2008 with the Allison. We have gone West every fall through the Rockies, usually on the U.S. highways. I am still on the factory brakes after 144,000 miles. At the last service, they still had adequate beef left in them. I like to use the tow haul mode in the manual configuration rather than in drive. I just like the control it gives me better.

[GeorgiaHybrid]

Charles,

 

The Jake brake (AKA Jacobs Engine Brake) on larger trucks is an engine compression brake that uses the engine valvetrain to brake the engine, not give it any fuel and release the compression just after the top of the compression stroke. Most inline 6's use a three stage brake where the engine will engage 2, 4 or all 6 cylinders to act like a brake. In my case, on the high side of the brake, our 13 liter Detroit will produce 505 braking horsepower. It is engaged by a switch on the dash on my truck but some have it on a stalk on the steering column and can be turned on at anytime. All you do at that point is back off the throttle and the brake will engage.

 

David

[cdlaine]

David....

 

Excellent explanation. Thank you . I'm guessing the first time you relied on the

brake system (on a steep decline) it took a some faith.

 

Traveler...

 

Have not towed thru Utah yet. Will make sure the TV is at optimal when attempting

that run... Those switchbacks require radio off attention ...no alpha waving.

 

Charles

[roy67ss]

Charles, you would really appreciate the turbo braking if you had the duramax with the Allison. The 8.1 doesn't have nearly the engine retarding effect that the duramax has.

[cdlaine]

Bill,

 

Interesting technology... I imagine a few iterations from now we will just direct "Siri" to maintain

speed at 62 mph regardless of grade .(or just correct as needed).

 

Roy,

 

I'm trying to get this current TV to the 20 year mark...I'm guessing the tech increases in the

next 7 years will lead to some major changes in truck capabilities. So... I just need to learn

to be satisfied with the current configuration. It does seem to be capable.

 

Charles

[Helipilot]

Duramax/Allison combo. Toggle the engine braking switch and ease down the grades. Loved it on our recent trip through Colorado. Hardly had to use the brakes at all. I agree, I'll raise my tumbler as well.

[cdlaine]

Roger,

 

Cheers ! Having lived in Colorado I am glad to hear of your towing satisfaction on the

down slopes of the Rockies. It is my understanding that those DRV's are born hefty ,

and only get heavier from that point.... sounds as if you have the perfect engine / tranny

combo for the job. Good choice.

 

Charles

[mptjelgin]

The 8.1 doesn't have nearly the engine retarding effect that the duramax has.

 

I question this statement. Gasoline engines have a throttle plate that tightly closes and have always provided significant engine braking. The introduction of automatic transmissions that keep the torque converter locked and automatically downshift allows the use of this engine braking to maximum advantage.

 

Without a throttle plate diesel engines have to rely on either a Jake Brake (the big boys) or an exhaust/turbo brake. An exhaust/turbo brake accomplishes pretty much the same thing at the throttle plate on a gas engines (restriction of air movement through the engine) but does it on the "back side".

 

Have you seen data comparing the Duramax to the 8.1L in terms of engine braking?

[cdlaine]

Mark,

 

Good thoughts..... I tend to get mesmerized when reviewing in lab test data comparing

apples to oranges. Subjectively, (and anecdotal) it appears both camps are happy with

the performance of the tow/haul grade braking in real world application. I'm thinking that

matching RV weight to the TV capabilities is probably the crucial factor. I can say I saw

a Duramax /Allison duelly with a tri-axle toy hauler blow by me on the 6% downgrade

and, that driver did not appear to have any control issues. Then again, I tend to drive

like a nun entering vespers.

 

Charles

[Kevin H]

In my ten years and almost one million miles of professional driving in buses and big rigs, going down hill was without a doubt the scariest part, especially on ice & snow. I, like you, saw many a rig blow by on the downhills and on flat stretches of I80 on black ice. Saw quite a few in the ditch later on. You are a wise driver to learn about, appreciate and use whatever retarders you have available.

A common rule of thumb is to go downhill at the same speed or lower than you did going up.

[mptjelgin]

We descended the Lewiston Grade on our way back from Idaho to Texas last year. Six miles of 6% - 7% grade dropping you about 2000 feet as you enter Lewiston from the north. They have at least five runaway truck ramps and more warning signs than I've seen anywhere else. With the tow/haul mode and engine braking on our truck the descent was uneventful. I used the service brakes a couple of time to rub off a little speed that built up on the steepest sections, but otherwise relied on engine braking all of the way down.

 

I will say that every single big rig I saw was crawling down that hill, and most RV'ers were as well. A couple of folks zipped on by and I didn't see them in any of the runaway ramps, so I guess they made it!

[cdlaine]

Mark,

 

I grew up in the Imperial Valley (California). The run from my hometown (El Centro) to San Diego , (and back) had grades of

6% for stretches of about 16 miles that take the driver from below sea level to about/over 4100 feet. This run involves some "summits"

and some interesting switchbacks around Jacumba. When big rigs lose it on the final stretch down to the Imperial Valley they do

not get a do-over. Very strong cross winds. Frequent over heated vehicles. The runaway truck ramps end is a big pile of sand .

Even having lived there for my first 18 years it still gets my attention every time I make the trip.... The length of those 6 % declines

can be surprising to the unexpecting driver. The last time I towed the run I was very thankful for good tires, and the tow /haul grade

braking. A bit un-nerving to see the skeletonized vehicle frames laying at the bottom of the bouldered canyons.

 

Charles