[A/S] Re: Exhaust Brakes can be Hazardous to Your Health!

[alweaw@xxxxxxxxxxx]

Conceptually, what you say is correct.  Is it a practical problem?  
That depends on the situation.  Automotive style exhaust brakes 
simply increase the exhaust backpressure, providing a modest 
retarding effect.  Bear in mind that diesel engines don't have 
throttle valves, so they don't have the pumping losses that gas 
engines with throttle valves have (basically trying to pull air past 
the closed throttle valve).  Gas engines have inherently more engine 
braking or retarding effect due to these pumping losses.  I don't 
think anyone would argue that the greater retarding effect of the gas 
engine makes it unsafe compared to a diesel.  Exhaust brakes on heavy-
duty commercial vehicles operate differently.  For instance, the 
Jacobs Brake hydraulically changes the valve timing and provides 
signficant retardation (in the hundreds of horsepower, depending on 
the engine).

A second practical issue is brake balance between the pulling vehicle 
and the trailer.  It's desirable to have the trailer brake 
application "lead" the pulling vehicle by a slight amount.  This 
helps avoid the trailer overrunning the tow vehicle, potentially 
causing a jackknife.  Short of working out this balance on a test 
track, most people are stuck doing this balancing by the seat of the 
pants (or most likely not at all).  In day-to-day driving this is 
probably a larger risk than that posed by the exhaust brake.

There are risks with using exhaust brakes as you've noted.  However, 
they also provide a margin of safety.  Certainly their wide use in 
the trucking industry (particularly in mountainous areas) indicates 
their value.  Truck operators/fleet owners wouldn't spend the 
multiple thousands of dollars it costs for a heavy-truck exhaust 
brake if they (and their insurers) thought it was a safety hazard.

My background - truck manufacturer test engineer and driver (22 yrs)