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RV Tech Savvy: Descending Steep Grades

Originally Published in MotorHome Magazine


I recently bought a 2017 Thor Windsport 29M with the Ford V-10 engine. On a recent trip to the Great Smoky Mountains I began a descent from around 6,000-plus feet and gradually downshifted in order to slow the descending speed. I continually had to apply the brakes hard, which made the brakes squeak really loud. Is there an after­market product I can install to assist the braking system on this motorhome? Since I had such a hard time slowing it down at 6,000 feet, I am hesitant to drive up to the Rockies where there are elevations of 12,000 to 14,000 feet.

Kenneth Barnes | Houma, Louisiana

The extreme heat buildup from extended downhill braking can cause the properties of the brake lining materials and other components to change. This can result in brake squealing, which may go away when they cool. The brakes can become glazed or the rotors warped. A greater risk is that the brake fluid boils in the calipers, which can result in a temporary complete loss of “pedal” until the fluid cools. If this worst-case scenario occurs, apply the parking brake, which is non-hydraulic, downshift as much as possible to control speed and use an emergency runaway truck ramp if one is available. This is why it’s so important to be vigilant, especially when driving a large, heavy vehicle, and to anticipate upcoming gradients. Plan ahead by approaching a long, steep downgrade at a slower speed and use a lower gear immediately – don’t wait until the brakes are overheated. If you deem that the brakes are still overheating, pull safely off the road to allow them to cool before continuing. Thousands of heavy vehicles descend the grades of the West every day using stock brakes by following similar procedures.

Regarding aftermarket products, the main upgradeable items are heavy-duty brake pads, which contain ceramic and other high-temperature-resistant materials, and premium high-temperature brake fluids. Exhaust brakes can be added to diesel engines, but currently they are not available for gas models.


Bathroom Odors

We own a 2011 Winnebago Itasca Sunstar 35F. Periodically the half-bath gets a foul odor that smells like an old diaper pail. I have tried everything I can think of to find the cause, including replacing the floor flange seal below the toilet, keeping the roof vent lid closed (due to the vent stack being close to the roof vent) and keeping the half-bath window closed. The black-water tank for the half-bath is directly below it. I checked the basement compartment where the macerator pump is located and couldn’t find any signs of wetness. If there was a hole or leak in the black-water tank it seems like the odor would be constant, but it’s not. I also use tank deodorizing chemicals regularly and drain the black-water tank often. Have you heard of other Itasca owners with the same problem or can you give me some advice?

C.F. Hommes | Shelby Township, Michigan

Sometimes dealing with bathroom odors like these can be tricky, but there are a couple of things that could be causing the odors. Up behind the sink in the half-bath is what’s called an anti-siphon trap vent device (ASTVD). This is a mechanical vent that opens to allow the sink to drain without emptying the P-trap. It consists of a rubber flap, sometimes held closed with a spring, that opens with the vacuum of the water draining from the sink. These frequently fail, as the rubber dries out and no longer seals. It is easy to remove and replace, and is available from most RV parts suppliers and from Amazon.com (search “Oatey 39012”). Make sure to only hand tighten when replacing, and consider applying thread tape to help seal it.

Other possibilities are that the black-tank vent pipe has become dislodged from the grommet at the tank, or has come apart at one of the turns in the wall, or has dropped and terminates below the level of the roof. A visual inspection, if possible, may determine if there is a problem. A flood test is often performed to check the condition of the drain plumbing system; however, I would recommend that a flood test be performed by a certified RV technician in a controlled setting. That, in and of itself, will not test the integrity of the upper vent piping, but will ensure the tank connections are good. It may also be possible to pressure-test the system with air, but that is a more advanced process, using a test ball for 1½-inch pipe.

Shifting Gears

The “Comment – Shifting Advice” letter in the August 2017 issue was really a shocker. Would you please explain shifting/rpm, etc.? I have no idea which to use when climbing hills related to rpm. I guess gone are the days of “D” for drive? The letter discussed maximum torque, efficiency, gears to use, etc. I, and perhaps others, do not understand lock-up torque converters, nor when I should change gears up or down, nor at which tachometer readings I should do so. My new Phoenix Cruiser on an E-450 chassis with a V-10 engine has more gears than my older motorhome. I’d like a simplified article about the significance of tachometer readings, which gears to select at which speeds, and so forth. Auto mechanics was not my major in medical school. I just want to go camping, enjoy my motorhome and not ruin the engine in the meantime.

MD in Michigan | Via email

The letter you refer to was at the upper technical limit of what I prefer to cover and explain in this column, which is intended for the layperson with a modicum of DIY knowledge, rather than engineers, professional technicians, etc. It was really about extracting the last bit of performance and efficiency. So don’t feel bad if you didn’t understand it. Virtually all motorhomes come with automatic transmissions, and they are designed to operate in most conditions without manual control over forward gear selection. The main exception (in my opinion) would be when descending long or steep grades, for the purpose of reducing the heat load on brakes (See “Descending Steep Grades” letter above).

The region you live in is relatively flat and shouldn’t require much driver intervention in automatic shifting. If your transmission doesn’t “hunt” up and down between gears when climbing a long grade, don’t worry about it. If it does hunt, select the next lower gear until you crest the grade. If you’re descending a grade and need help controlling downhill speed, slow down and downshift a gear or two as needed.

The Ford chassis is equipped with a tow/haul mode, which is switched on at the end of the gear shift stalk. This changes the transmission programming to optimize the shifting points for carrying or hauling a heavier load, and will also allow the vehicle downshift on hills to help slow the vehicle. With ordinary driving on level ground it’s probably not necessary to use tow/haul; however, when towing or when driving in mountainous terrain, I would recommend using it.

Many motorhomes don’t have a tachometer, and they are not essential for routine operation (although many folks like to have one). The latest E-450 chassis equipped with the 6.8-liter V-10 have a six-speed automatic, and torque peak is at 3,250 rpm and peak horsepower is reached at 4,250 rpm. The engine’s best efficiency under full load is at torque peak, and best acceleration and power at the horsepower peak (but efficiency drops off). So, for long upgrades you may want to stay near torque peak, and for short bursts – like merging onto highways – run it up to the horsepower peak, but not any higher.

Battery Goes Dead – Comment

In “Battery Goes Dead When Disconnected – Comment” in the October 2017 issue, reader John Gaines suggests installing a blade switch to disconnect the batteries. May I strongly suggest, from a safety viewpoint, to install a marine-type battery switch. These are fully enclosed and thus eliminate the probability of generating a spark.

Lutz Moeckel | Garden Grove, California

Thanks for writing, Lutz. You have a good point, as hydrogen gas can accumulate around batteries, especially if they have just been charging, or battery-box ventilation is poor. A quality switch designed for marine use, such as those sold by Perko, are considered to be sparkless and safer for this application.


Ken FreundMotorhome DIYRV Tech SavvyTech topics

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