RV Expert Bruce Bernhart Discusses Important Safety Considerations When Using Auxiliary Braking Systems

In 2008, Motorwatch issued a very informative report on the safe RV navigation of steep grades

. We continue the discussion with a look at the proper use of auxiliary brakes when ascending and descending hills and mountains.

If your vehicle is equipped with an auxiliary braking device (engine brake, exhaust retarder,

transmission retarder or driveline retarder), be sure that it is turned on. Use it above 1,800

engine rpms in order to get the maximum braking horsepower. If your braking device does not

have a preselect feature, you will have to manually select the proper gear. The proper gear allows you to use the engine or transmission to help you maintain a safe speed on a mountain grade.

The descent

These instructions pertain to descents longer than a mile or two and with descent angles

greater than four percent. Lower your vehicle speed enough to downshift your vehicle into the

gear you feel is safe to start down. Take into consideration curves or anything else along the

way that may affect your descent. For example, if there is a 25 m.p.h. curve one mile from the bottom, don't start at the top of the hill in fourth gear, which has a maximum speed of 65

m.p.h. On a steep grade, your brakes will become hot as you try to slow down for the curve. If

your speed or rpm level increases rapidly ,you're in the wrong gear. It's critical that you slow the vehicle down enough to downshift one gear.

NOTE: Regardless of engine type, watch your speedometer and tachometer to see that you

have a gradual buildup in each. As you approach the maximum limits, apply light pressure to

the brake. On a mountain grade, the proper braking technique in normal situations is to apply

approximately 12 pounds of brake pedal pressure to gradually slow the vehicle down. Avoid making a hard application of the brakes, as this will cause excessive heat buildup. Likewise,

applying light brake pressure all the way down the hill will create excessively hot brakes, which are ineffective in an emergency situation.

Bring the engine rpms down to approximately 500 rpms below the maxi- mum rating (7 to 10

m.p.h. below the maximum speed) then take your foot off the brake pedal. Continue to repeat

this process as you go down the long grade. If you have selected the proper gear, you

shouldn't have to do this more than three times every two miles. The light pressure applied to the brake, combined with a sufficient cooling period between applications, will ensure that the

brakes will stay cool enough to make an emergency stop if necessary. If your vehicle is going too slowly (way below maximum speed and rpms in that gear and never having to brake), you can manually shift one gear up.

As an alternative to the above procedure, slowing the vehicle sufficiently to drop into the next

lower gear (one lower than in the above procedure), combined with the use of the auxiliary brake, may allow you to descend the mountain without even applying the service brake.

Special considerations

Gasoline engine motor homes: Since motor homes with gasoline engines have fewer gear

selections than diesel engine coaches, you'11 likely need to start any descent longer than three miles and with a three percent or larger grade in second gear.

Diesel engine motor homes: Be sure that your auxiliary braking device (engine brake,

exhaust retarder, transmission retarder or driveline retarder) is turned on. If operated by a foot

valve, place your foot near it. Remember that these devices give maximum braking assistance at high engine rpms, which is why we recommend keeping the engine rpms

near the top of the band at all times during your descent. Allison World Transmissions, which

have six speed ranges, have no torque lockup feature in first gear. That means the retarding device will work less effectively in this gear. With Allison 542, 543 or any fluid drive transmission, the retarding device will also be less effective.

The additional weight of a towed vehicle will cause you to use the brakes more in the

mountains than otherwise. If the grade is long and steep and you don't have an aid in

maintaining a safe speed, it may be better to disconnect the towed vehicle and have your traveling partner drive it down the mountain.

Trucks towing fifth-wheel or traveltrailer (diesel or gasoline engines):

Many of the transmissions on trucks disengage or freewheel when you take your foot off the

accelerator, which is counter - productive when you want the engine to help you slow down. Some of these will retain the which prevents freewheeling, if you manually select the gear you want to use to descend the hill.

RV Expert Bruce Bernhart Discusses Important Safety Considerations When Using Auxiliary Braking Systems

By: Bruce Bernhart

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