Mountain Driving with SMI Air Force One

[michguy]

In September, I will be heading for Albuquerque from Michigan via Denver, Colorado Springs, Wolf Creek Pass & Durango,CO. I will be driving my 2005 National Tropical w/ C-7 Caterpillar 350 HP Diesel w/ Engine Brake (Pac-Brake). I will be towing my 2007 Saturn Aura. I have the SMI Air Force One braking system for the toad.
In another forum, someone said that if I engage the Engine Brake, my Service Air brakes on the coach and the toad were no longer operable.. My question is, " With my setup, how would be the best way to negotiate a grade like Wolf Creek Pass ?

[Wayne M]

Mitchguy,
I don't know about Wolf Creek Pass, but this past year I went up US-101 to Whidbey, then over through Idaho, Wyoming, Colorado, and points South again in a 340HP DP (Cummins) on a 40 foot Winnebago pulling a Saturn Vue with SMI AF1. I never encountered any problems with the exhaust brake. I was on some 6-7% grades with no problems. Let the exhaust brake do it's job and occasionally stab the brakes if you are speeding up to get back down below speed, then when it builds up again, stab them again. Repeat as necessary, but for me, between the exhaust brake and Allyson transmission - no problems.

[Submustang]

I agree with Wayne M. I can't get anywhere from my house without going over some pretty good passes. I leave my pac-brake turned on almost all the time and have never had any problems. My service brakes are fine and the AFO does a superb job on my 5K lb pickup.

[Parkerrs]

Quote:

Originally Posted by michguy In another forum, someone said that if I engage the Engine Brake, my Service Air brakes on the coach and the toad were no longer operable..

Whoever told you this knows absolutely "nothing" about how these systems work, let their advise go in one ear and out the other.

The engine brake or an exhaust brake are "supplemental" braking systems on a diesel coach. They both use engine compression, i.e. in different ways, to help slow the coach via the drivetrain. Increased "engine" braking are what they provide.

Niether of these is connected with or to your "service" brakes, which are the ones connected to the brake pedal on your coach. They are to be used in conjunction with each other in a fashion such as Wayne explained.

When the engine brake is on it will slow the coach by holding back on the drivetrain when you completely let off of the accelerator pedal. Your SMI will not be active at all until you step on the coach brake pedal at which time you will be applying coach brakes and toad brakes. The engine brake will continue to function also until you either step on the accelerator, switch it off or reach a speed of under 20mph. The low speed shut off for the engine brake varies but usually between 15-20mph is it.

[michguy]

Thanks to all of you ! I've been stewing over the " non-active service brakes" for quite a while. I think I'll be just fine this October, between Colorado Springs and Durango.
michguy

[Robi.1014]

Michigan,

Let me offer a nugget not mentioned above: 4th gear of your Allison transmission....a great gear!!

When you're going downhill and want to use your exhaust brake, if you're doing under 65 MPH, the computer will shift from whatever gear you're in (5th or 6th) into 4th. This slows the coach nicely, and if the grade is REALLY REALLY steep, some additional foot-braking will help you keep your rig in the 45-to-55 mph range...a fairly safe downhill speed. BUT........ When you remove the exhaust brake, the tranny returns to 5th gear and then your RV starts picking up speed again.

What I've found:
To stop the braking-slow-down, speed-up, braking, speed-up cycle, I apply the exhaust brake (the Allison then shifts to 4th) .... at which time I press the "down arrow" button on the transmission control panel. Press twice if you were in "drive" (6th gear), or press once if you were already in 5th (the preferred "down hill" gear). Now with the Allison continuously in 4th gear, I can remove the exhaust brake and/or re-apply the exhaust brake but the tranny stays in 4th. Maintaining 50 or 55 mph becomes very simple using this technique. Watch your RPMs which is to say: don't let the coach speed-up to 60+ MPH while in 4th.

You also asked about SMI (on the toad, I presume). I've got my SMI sensitivity set so that the above 4th-gear technique (and the on-again/off-again use of the the exhaust brake) does not cause the toad's brake to apply. But if the RV is speeding up too much with the exhaust brake applied (and the tranny in 4th), a solid application of the foot brake also causes my toad brakes to apply.