Remember the First Law of Thermodynamics from high school physics? Energy cannot be created or destroyed; it can only be converted from one form to another. This principle of "conversion" underpins virtually every mechanical process that makes a vehicle go, and stop. Every time you start up a vehicle you're converting potential energy to kinetic energy, and every time you stop you're converting the kinetic energy right back into potential energy. When a heavy truck's engine brakes are engaged, a very dramatic energy conversion takes place...
"The engine brake comes under some pretty stressful conditions," says Bruce Sebring, VP sales, Pacbrake Company. "What we're doing is we're opening the exhaust valve at TDC on the compression stroke, and releasing engine compression, and that sometimes puts pressures inside the engine brake housing in the 3,000 to 4,000 psi range.
"It's not uncommon for an engine brake to lose 25 percent of its efficiency at the quarter million mile mark," Sebring says. "It loses efficiency over time, and you never really notice it. It just gets progressively weaker and less effective, and if you don't do maintenance on it, you can accelerate the wear of the engine brake housing itself. Then once that's worn out, you have to replace the housing. But regular maintenance will prevent that, and will keep the engine brake at the efficient level, and will increase your ROI.
"So there are some critical control components in there that need to be addressed on a fairly regular basis," he says. "Fairly regular to me is about a quarter million miles and up you should go in there and, shall we say, freshen up the engine brake. Whenever you're under the valve cover, running the overhead and injector head gasket, etc., the labor's already done, so it's a simple matter to then add these components to the engine brake and get it back to 100 percent efficiency."
"We try to link maintenance of the engine brake to engine overhauls," says Paul Paré, director of marketing for Jacobs Vehicle Systems, maker of the "Jake Brake."
"When you're taking advantage of labor, you can use a tune-up kit during that overhaul," Paré says. "A lot of companies will have scheduled recommended overhauls on their engines, and during that time when the valve cover's off and the brakes are removed, the labor's already spent. So we say, while you're doing an overhaul, put a tune-up kit in there at the same time. It just makes sense. That way you're using genuine parts, and you're restoring your performance."
The difficulty with engine brake maintenance is that drivers can't always tell when the performance of the brake has slipped. According to Paré, engine brake effectiveness is difficult to measure:
"To fully understand performance degradation, we need to get a sample truck that has 400,000 or 500,000 miles on it, put it on a dyno, and check for performance. What is the degradation? Then we put the new 'tune-up kit' parts in and reinstall it and put the truck back on the dyno to check the performance."
Paré says that his company is working with engine OEMs to harmonize maintenance intervals to make the hour-long engine brake tune-up as inobtrusive as possible. As a part of that effort, Jacobs will begin a major training campaign in the coming year to get fleet customers to regularly tune up their engine brakes when they perform engine overhauls.
Those fleets that plan to hold onto their trucks for an extra year, or buy used trucks, to avoid purchasing trucks with '07 engines will need to keep engine brake maintenance in mind.
"Ninety-nine percent of Class-8 trucks built today have an engine brake of someone's manufacturer on it," says Sebring.