Shifting Allison 3000

[RIDER FAN]

I normally push "D" on my shift panel , release air brake and go.......up hill down hill.I never use shift pad. Last week south of Vegas in some steep hills i did not slow down enough [and in sixth gear] with exhaust brake on I gained speed from 65 mph to over 75mph. The speed limit was 70 but it seemed i was REALLY going with 4 door jeep in tow. The exhaust brake was hardly doing its job and my wife was white. I instantly thought I should down shift to fifth or fourth but out of fear of damaging transm at high rpm i did not. I later learned the transm will not down shift out of it's rpm range anyways. So , even though I thought i was pretty good behind the wheel this was a humbling experience , the lane was clear but i was not in full braking control and riding my brakes for five seconds off and on didn't do much except heat up brakes.
So rather then think i know it all,and possibly damaging transm, how do you all approach driving in Mountain grades besides not being stupid and just plain slowing down.....I learned my lesson and am a lot better driver then the clown act i pulled off. What i am interested in is gear selection before going down a STEEP grade. I read it is a fact that a lower gear would create more engine rpm increasing exhaust brake effectiveness ?? [My MH is 40' Endeavor with 400 ISL] may seem like a no brainer but i have gained invaluable info from this forum.

[blang]

I'm not sure why but I've found that having the cruise control on over-rides the exhaust brake to some extent. Turn off your cruise and you should be fine.

Sorry, can't answer your specific question about down shifting.

[mmartin]

gear selection is determined by your engine rpm's....if approaching a hill you need to gear down and keep the rpm's between 1500 and 2300 and the same goes for defending the hill. Keeping the rpm's up in that range will also help from overheating. Definitely use the exhaust/engine brake when descending

[Pigman1]

Rider Fan, what you experienced is exactly how the ISL/3000 combo with a compression brake is supposed to work. As to what gear to select and when, I guess I don't do it that way. When we're at the top I make sure I have my speed under control and I select the speed I think I'd like to descend at. Yes, many times it's a guess, but obviously slower for a 2 lane winding road in Alaska than on I-10 dropping down into Palm Springs. Once there, be sure your "economy mode" light is off and you've selected high for the compression brake. If you've selected 60MPH (in your head) and you see your speed starting to creep up, you need to lower your speed to 55 or even 50. Get on the service brake to bring you to that speed NOW. Once there, feet on the floor and see how that works. If you continue to slow on only the compression brake, your selected speed is a bit too slow. If you tend to speed up, it's too high and you need another service brake application to get you lower. Don't "ride" the service brake, get on it like you mean it. You might have to do this procedure 3 or 4 times but eventually you'll hit it and be able to head down the hill with feet on the floor. Of course, once things stabilize, the slope of the road will change and you start over again with a new selected (guessed) speed. With a bit of practice, this will become second nature. We regularly ride mountain roads in the Rockies, and have run 6 times to Alaska so we're no stranger to the ups and downs. After you start to get it right, it's almost a mind game to get to that ideal speed on the first pick, and of course the road builders are always changing the slope to screw you up. Have fun and enjoy the trips.

[ru499]

Old truck driver tip. Go down the hill in the same gear you went up the hill.

[dennis45]

Sounds like you already had a lesson.

First rule, don't go down the hill any faster than you went up.

When you turn on the exhaust brake you will see the transmission selector indicate second gear. As you now know, it will not downshift any lower than engine RPM will allow to prevent over speeding the engine. So, when you reach the top of the grade at say 50 or 45, have the exhaust brake ON and start down the grade. The transmission will want to upshift as speed increases (to prevent overspeed). When that upshift occurs, apply the service brake firmly to reduce speed and cause the transmission to downshift back into the lower gear you started out in. Release the service brake and continue down the grade applying the service brake only as required when the transmission upshifts until you reach the bottom.
On a very steep grade of say 8% or higher, I manually select the gear at the top of the grade that I was in coming up. Say 3rd or 4th gear. I find this gives me better control and, I can still apply the service brake to allow a downshift to a lower gear if needed.
The key is not to gain excessive momentum that you cannot control by the intermittent use of the service brake. When you do apply the brake, do so firmly to reduce speed and Do Not Pump the brakes.

[Lt Dan]

Pigman and Dennis both have great advice. Another thing to keep in mind when using the exhaust brake is over revving. The computer will not allow the engine to over rev so if the exhaust brake has it down in 4th gear and the speed creeps up to where the RPMs are reaching max, it will upshift to a higher gear. That will get your attention very quickly. Use the brakes to keep your speed down by "stab" or pump braking occasionally, then get off of them. Don't ride the brakes, just use them for short braking moments. I will normally shift down at the top of the hill and go down in about the same gear as I came up, if the grade is the same. Don't be afraid to use the shift pad to stay in control. I will even down shift to 5th when starting up a highway grade instead of waiting for the speed to drop enough for the cruise control to downshift. That will usually eliminate the 4-5mph drop in speed before it automatically downshifts. 6th gear is just an overdrive and even at 70mph, 5th gear is only around 2000 rpm.

[barmcd]

My PAC brake won't work with the cruise on. I hit the cancel button or tap the brake to turn the cruise off and then use the PAC brake switch. Also, my PAC brake won't work in first gear.

Like others here, I will manually downshift at the top of a hill if I know it's coming.

[wigginsjsr]

I have a three speed engine brake. It will not engage with the cruise control activated.

[webslave]

The arrows (up and down) on your pad are there for a reason and they are your friend. As already mentioned, you want to keep in your power band and preferably not with the pedal floored. If you keep the pedal floored the system tends to dump too much raw fuel into the pistons and blow-by (diesels all suffer blow-by it is how they work and why their oil turns black in a short time) and blow-by of fuel will dilute your oil and lower its lubricity; use the down arrow to keep the transmission in a lower gear so that you remain in the power band and the pedal is not floored.

The OTA rule of thumb for going down in the same gear you went up in is older than I am and has a lot of truth in it. If there is a "level area" at the top, go ahead and upshift, but, when you start down the other side; exhaust brake on, downshift and use the stab method to scrub excess speed to maintain a good steady, controllable speed down the grade.

The transmissions in these rigs (Allisons) are unbelievably tough and they enjoy working...that includes controlling shift points manually when needed; again that's what those up/down arrows are for, use them, they are your and your engine's friends

[Texasranger]

When going down hill its better to get on them a little harder , slow down fast, then get into correct gear. Riding breaks is not a good idea.

[DD788Snipe]

All great advise. Just a note. On some coaches the exhaust brake works with the cruise control on and will activate when your speed gets 5 miles over what it is set at but it doesn't tell the transmission to downshift unless you tap the brake and release the CC. My rig is programmed that way. I tend to drive the same as webslave. I just finished a 4600 mile trip for the summer. I've been up and down both sides of the Rockies in gas and diesel rigs and most all of the passes in the west. Your exhaust brake is your best friend and you will come to rely heavily on it. I was starting down the west side of Flagstaff the other day and when the AUX BRAKE light on the dash didn't come on I almost panicked but a quick cycling of the switch and it came on and I breathed a sigh of relief. That's how much I rely on mine. I know the Mountain Pass grade your referencing very well. I live 100 miles south of it just above the Cajon pass. If you take all the advise you have in this post and put it to use you will become very comfortable in a short time with any of the grades you will encounter here in the west and there are some steep ones. Good luck, be safe and we'll see you out there on the road.

[Dutch Star Don]

"RIDER FAN"......I can give you some advice on driving your coach, because I had the same coach for ten years (2005 Diplomat).

To start, and not to offend anyone, the old saying of going down a hill at the same speed you went up, is an old adage that doesn't apply to many modern coaches. My 05 Diplomat had the power to climb 6% - 7% grades at 60+ mph, even while towing, yet the Exhaust Brake was incapable of holding the coach back at those speeds on a 6% - 7% downhill.

Your Allison will NOT allow the engine to over rev and will NOT downshift if the rpm's are too high. Your exhaust brake has just enough power to MAINTAIN downhill speed when turned on at 55 mph or less on grades that are 5% or less.

Anything over that speed and your exhaust brake will do little for you. Anything over 5% and your coach will gain speed proportionally to the steepness of the grade.

Your first downshift when the exhaust brake comes on, is typically 6th to 5th. Again, only a little help on slight grades. Your next down shift will help, but still won't hold the coach back. On my Diplomat, I eventually had to get to 44-45 mph, a downshift to third, before the coach would hold on grades above 5%. So.....if you know it's a steep/long grade, you'll want to get down to the 44 mph speed. I short grade, you'll be back on flat land before the coach builds too much speed.

Here's the problem.....descending grades at 45 mph usually brings an onslaught of semi's and other RVers roaring down your back side. Many will say, who cares, but it can be disconcerting and I hated it. It typically took a lot of work, both selecting speed, stabbing brakes and paying attention to the overall grade when using the exhaust brake.

This may not be the answer you're looking for, but it's what I found worked best for your coach after ten years of driving my Diplomat all over the mountain ranges out west. The only one where all the rules go out the window is the Eisenhower grade in Colorado.

When I owned the Diplomat, I was towing a Chevrolet Silverado 4 door. I knew when I eventually changed coaches, my next coach would have an engine brake. The newer coaches allow the engine brake to work with the cruise control and automatically adjust speed on steep grades. It's now a lot less work and I can descend most grades at whatever the rest of the traffic is doing.

[Skip426]

Crest the summit of any pass at 40>45 , it's much easier to increase speed than slow down .