RV'ing : the Exhaust Brake
How best to brake a heavy Recreational Vehicle ?
Some of my readers may have wondered about my multiple references to our exhaust brake. Perhaps a word of explanation would be in order.
An exhaust brake is an additional braking system, and an efficient tool that we wouldn't want to do without any more. On long and steep descents, this brake delivers strong and continuous braking power, without even having to touch the traditional foot brake.
An added psychological advantage is that it provides a greater sense of security to the driver, when descending steep slopes.
On our RV there are three brake systems.
The truck is equipped with modern and rather large disc brakes, that can efficiently brake its own weight plus cargo.
Fifth Wheel brakes
Our Fifth Wheel was originally equipped with electric drum brakes, that function quite well, at least when it is dry.
Furthermore, we had opted for three rear axles, so that both the total braking surface of the six tires and the brake shoes is rather high. With these brakes, the RV weight of approximately 14.5 tons can be slowed in a relatively short distance.
Veteran drivers know however that drum brakes may show fading problems. This means that they can get very hot when they are used constantly, such as during a long descent. This is because the internal brake shoe cannot cool quickly enough between braking episodes.
A second problem with drum brakes is water, because the ventilation openings of the brakes, in addition to the cooling air, can also suck up water when it rains heavily or when driving through puddles. The brake shoes get wet, and braking power decreases dramatically.
To solve this problem we replaced the drum brakes with disc brakes.
The Exhaust Brake
For long and heavy Recreational Vehicles it is therefore certainly recommended to slow down the combined weight of the tow vehicle and trailer, especially on long and steep descents, or by heavy rain. This avoids having to use the foot brake too frequently, which in turn avoids overheating. So we installed a third kind of brake on the truck, an Exhaust Brake.
Diesel engines, unlike gasoline engines, provide practically no automatic braking when the foot comes off the gas. On steep slopes the combined weight of the vehicles soon leads to an undesirable increase in speed.
The Exhaust Brake uses the exhaust gases and a compressor to partially block the exhaust pipe, so that the diesel engine cannot refill itself as well, and therefore slows down when the foot comes off the pedal. This contraption is simply a godsend !
Long slopes up to 5% (i.e. 5 cm per meter) can easily be descended in fourth gear, without even having to use the foot brake ! For steeper slopes or very long downward stretches, we simply shift to a lower gear. We even use the exhaust brake in heavy city traffic, or when leaving the motorway.
An additional technical advantage (for the technocrats...) is that the engine valves, that are heated up very strongly during a steep climb, are not allowed to off cool too rapidly in the subsequent descent, and therefore the risk of deformation is far smaller.
Practically all of the heavy commercial trucks are equipped with some version of an exhaust brake, although large trucks usually have a Jake brake. This brake is even more powerful, but it also produces far more noise. Its use is often prohibited in cities.
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