Well this is the big reveal, the major upgrade we have been wanting ever since our scary downhill ride in Sedona. Though now more prepared for such events, we experienced several more downhill runs, particularly leaving Joshua Tree and coming into Carmel Valley, that I can only categorize as “not fun.” Such incidents increased our sense of urgency to improve Kahuna’s braking ability, and online research revealed that retrofitting an “engine brake” onto our Detroit Diesel engine is perfectly doable. Thus, two weeks ago when we picked up the bus from Ted following the reverse gear repair, we made arrangements to come back for the Jake Brake install.
Here is the gist of it: Trucks and buses are so heavy that their brakes are often insufficient to the task of slowing and stopping them on long steep downhill grades. They become overheated and less effective. Exhibit A: The Big Kahuna. Thus you often see warning signs at the top of long downhills advising trucks of the percent grade, to check their brakes, and use low gears. Part of the problem is diesel engine mechanics; for most diesel engines, even when no fuel is applied, the full amount of air is sucked into the cylinder, compressed, and that energy applied to the crankshaft.
In the late 50’s and early 60’s Clessie Cummins, of Cummins Diesel fame, developed a method of retrofitting a device on the rocker arms inside the engine that, when activated, would open the engine exhaust valves such that the compressed air is not applied to the crankshaft, but rather the energy is absorbed by the engine, effectively turning it into a brake. Or as Ted explains it, it turns your engine into an air compressor. We will be able to turn it on and hold our speed on even significant downhill runs without touching the brakes at all. We just completed our test drive, and it works as advertised on the limited hills in this area, and exactly according to spec in terms of when it engages and how. This major upgrade gives us a lot of peace of mind for our future runs through mountain areas. The only down side is that the modifications required much larger valve covers, and one of them is so large that the rear doors do not close. We will modify the doors with a professional looking bubble to accommodate the valve cover, but for now Ted just cut a clean rectangle out.
Incidentally, engine brakes are often called Jake brakes because the first manufacturer/distributor was Jacobs Vehicle Systems.