Allison Trans & 10% Grade

[Dutch Star Don]

Wow....Did we make a wrong turn. On the way to the Grand Tetons/Yellowstone last week we took Hwy 31 to Hwy 33 to Jackson Hole rather than Hwy 22. The GPS mislead us . It was a steep winding road, but I saw a couple of large trucks and felt okay. We reached Hwy 33 and the first sign we saw was 10% grade!!!!!

There were a couple of turns posted at 35mph that we could only make at about 20 mph with my foot to the floor and manually downshifting. We were towing our truck.

We felt better once we hit the top, only to find several miles of 10% down grades. Even at 35 mph with the exhaust brake on and stabbing the brakes I couldn't slow the coach and could smell the brakes getting hot. I tried manually downshifting, but it would shift back on it's own.

I had to pull into a turn out to let the brakes cool. It was soooo steep that the parking brake wouldn't hold until I rolled up to a rise (storm cover) in the turnout.

I should have unhooked the toad and have the wife drive it, but she ran and hid in the bedroom until we were down out of the hills.

Finally, I made the descent down the last 4 miles. I put the Allison in 1st and started down the hill. To my surprise, it didn't upshift. It held the coach at 15 mph all the way down the hill. This was something I didn't know it would do. I thought it would upshift once the rpm got to high. I didn't get a chance to see if it would do it in 2nd for fear of shifting out of 2nd automatically.

Hopefully I'll never see another 10% grade, but it's nice to know you can lock the Allison in 1st.

[AFChap]

Those kinds of "hills" are not a lot of fun in a large coach, especially with sharp turns mixed in!!! My Allison will normally downshift to whatever gear I have manually selected IF I will slow the coach enough for that to happen -- it WILL NOT downshift if it senses the speed is too high for the engine to safely downshift. We have climbed a few hills in as low as 2nd gear, and descended in the same until safe to manually shift to a higher gear. The key on the downgrade is to get into that lower gear at the top before your speed is too high for the safe downshift, otherwise you have to brake to a low enough speed to make it happen.

[MonacoMama]

Don...first of all- I am glad it all ended well ...We have too many new members here lately for you not to be around to respond!...I need you to help me understand better..pretty please!

Originally Posted by Diplomat Don

Wow..... I tried manually downshifting, but it would shift back on it's own...Can you explain the difference of this downshifting" and the next "downshift" procedure.... I put the Allison in 1st and started down the hill. To my surprise, it didn't upshift. It held the coach at 15 mph all the way down the hill. This was something I didn't know it would do. I thought it would upshift once the rpm got to high. I didn't get a chance to see if it would do it in 2nd for fear of shifting out of 2nd automatically.

Hopefully I'll never see another 10% grade, but it's nice to know you can lock the Allison in 1st.

PS...Did Mary take any photos of the ride down hill?

[Denali]

This spring we crossed Death Valley east to west. The 9% grade coming out of the valley was 25 MPH in second gear, wide open throttle, the whole way. Coming down, I put it in second, PacBrake on, and used the service brakes only when necessary to keep it from upshifting to third.

Like you, our brakes overheated, and the park brake would not hold it on the grade in the first turnout I found after they got hot. I sat on the service brakes until the rears cooled enough to hold it. We ate lunch and started down again.

This time I put it in first and used the service brakes to keep us down to 10-11 MPH. That did the trick.

Whew!

Now, it wasn't as bad as the 18% "Sea to Sky Highway" we took in BC a few years ago...

[Ed_G]

I'm kinda wondering about the "GPS unit misleading " you part. Could you elaborate? What can it offer to help prevent such a routing choice error?

My 30 foot Trek and little Scion Toad would probably not have as much difficulty as your DP and truck on such a steep grade, but I'm quite willing to avoid such routes, anyway !

[Norm4015]

I have driven that very long 9% grade heading west out of Death Valley. I started down in 2nd gear with the exhaust brake on and I never had to touch the foot brake. It was a scenic and relaxing drive, but the highway was steep and narrow going back up the mountain.

[Happycarz]

I also drove a couple of those scenic route to/from Yellowstone N.P. last month. You know, the ones on the map with the little dots next to the route. Well, two of them turned out to be 10% grades, up and down. On the way down I used 1st and the PacBrake. Normally the exhaust brake will turn off at low speed in 2nd and not engage in 1st. If you select 1st, then the exhaust brake will work in first. Many Monaco owners are not aware of such. I don't know of other brands, but would think if equipped with the Cummins/Allison combo it would behave the same. If you haven't tried it , give it a go.

[Dutch Star Don]

HappyCarz......That's why I posted. I don't think many know that it will hold in 1st gear with the PacBrake on. I certainly didn't.

MonacoMama.......If you're on a steep grade and start downshifting, the Allison will automatically upshift to a higher gear if the engine speed gets to high. You're then forced to use the brakes to slow it down again.....but....you can put it in first and it won't upshift.

Ed_G.....I have an in-dash Pioneer unit and a portable Magellan that I run simultaneously. The in-dash has the entire trip loaded and the portable is for looking for campgrounds, rest stops and other POI's. We didn't really look at a map closely for the roads into Jackson Hole. There was a choice of two and both GPS units picked the short/steep one. I shold have checked before I was forced to commit.

[nutensteve]

Don....Glad you made it safely and good to know about the exhaust brake working in 1st gear. I made the trip down Tioga pass from Yosemite to Hwy 395 last year and was a little un-nerving. I'm not sure of the grade % but the drop off is nasty. Nita spent the entire trip on the opposite side of the coach and never looked up 'till we reached the bottom.

[becker]

Boy!..... now that's scary. Presently considering a trip across those states, my question is..... When you pre-flight your trip, how do you find out where those grades are?

My GPS has got me in trouble a couple of times so I don't rely on it that heavily. I have been a map guy so long that I feel more comfortable with a map in my hand.

Thanks.

Becker

[Denali]

Originally Posted by becker

Boy!..... now that's scary. Presently considering a trip across those states, my question is..... When you pre-flight your trip, how do you find out where those grades are?

If you stay on the interstate system, you don't have to worry about it. Grades are limited to 6-7% on those.

In any case, your Dynasty has a real Jake Brake. Our rig, like the Diplomat, has a PacBrake. Totally differently technology, and the Jake Brake is much more effective. With your rig, you don't need to worry about those steep grades as long as you don't try to descend at high speed.

In terms of climbing the grades, it's not a problem. These coaches are engineered to operate at wide open throttle indefinitely, as long as you haven't modified the engine.

Have a great trip. As much as we like boondocking in the desert, the best scenery is in the mountainous areas, in my opinion.

[Sixpack98]

Don,
Bet your life flashed in front of you a couple of times and no doubt there are impression of your hands on the steering wheel. I think I had a nighmare of a 10% grade once. At any rate, you recovered and applied what you have learned and things turned out well. Except for the possible stammering for a few hours afterward. I've encountered a few 8+ grades and not anxious to try a 10%, especially on a narrow windy road. There are more than a few challenging roads in and out of Yellowstone. Last time we were there we came into the Yellowstone area from the southeast on 287 which was not a bad road just keeps you on your toes. We left from Jackson on 189 to 26 to I 15 at Idaho Falls. So, did you end up on 22 just south of Jackson?
Several months ago I think Happycarz (Harry) discussed how to engage the PacBrake with the Allison in first gear. Have not had a chance to use it and happy to see it worked for you.

[blacktie.shooter]

Originally Posted by becker

Boy!..... now that's scary. Presently considering a trip across those states, my question is..... When you pre-flight your trip, how do you find out where those grades are?

Becker, I don't know where you live, but there is a book you can buy at CW (in the West, at least) that spells out in detail all of the major, and from what I can see, a good share of minor grades on highways in the Western States.

I have no clue if there is an Eastern version, and my copy is in the coach right now, so I cannot give you the exact title. I believe it was originally designed for over-the-road drivers, but it's a great addition to any coach library.

If anyone needs it, I will be at the coach today, and can give you more specifics when I get back.

[bobinaz123]

Mountaindirectory.com has maps on CD with grade and curve info for the whole country divide by East and West files.