From: Bjorn Brandstedt (super_deuce@hotmail.com)
Date: Wed Nov 10 2004 - 01:02:44 PST
The multifuel engine DOES have a small amount of engine braking capability
due to the compression of air (like all diesels) when the rolling motion
turns the engine over with very little fuel injected. Most of this
compressed air is turned back into torque and horsepower (when multiplied by
the rpm), BUT some of the heat created when the air is compressed is
transferred away by the coolant and dissipated in the radiator. This heat
dissipated and the engine's natural resistance to motion is its braking
horsepower.
This "negative" horsepower is a function of rpm and the higher the rpm the
higher the braking power of the engine. I made test runs some time ago and
estimated the maximum braking horsepower of the LDT465-1D to be about 50Hp.
The xhaust brake can double that.
One can calculate how much power it takes to drive a vehicle at a certain
speed with a certain gross weight when descending a hill of a certain slope.
I have done that and confirmed it with my truck, which was weighed for the
occasions.
I also concluded that to drive down the hill in the same gear as you ascent
it would require the addition of some braking power from the service brakes.
For a long descent, go even slower and use no service brakes! But driving a
loaded deuce at 4mph may not be practical on the highway.
The bottom line is that the higher the rpm the higher the braking power.
The exhaust brake lets you drive faster downhill because it adds braking
power.
If you shift into a higher gear (going down the mountain) and have to rely
on the service brakes alone there is a good chance that the brakes will
overheat and fade. At this point you stand to lose a lot more than just your
brake linings.
Williams patented the exhaust brake in 1957, so it has been around for a
while.
The fact is that the engine's cooling system can dissipate a lot more heat
for a longer period of time than the service brakes, so why not use it
especially downhill when the engine cools off anyway?
Bjorn
>From: "jatonka" <jatonka@telenet.net>
>To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
>Subject: Re: [MV] M35 Exhaust Brake installation
>Date: Tue, 9 Nov 2004 20:42:31 -0500
>
>What about the instruction in the truck driver's manual that says descend
>the hill in the same gear that you ascend it in? Isn't that about engine
>braking? What about burning the wheel brakes out or glazing them so badly
>that they won't even slow you down on the way to the bottom of the hill
>with
>the school at the bottom at that 20 mph turn? How about the signs in all
>the
>mountain states that say HILL trucks use low gear? I am a truck driver,
>have been since I was 15, I'm 53 now. I've always geared down, never ran
>off
>the road to lost brakes, Gone a hundred and eighty thousand miles on brake
>linings and never ruined a motor by using Jacbs Brake or exhaust brake on
>smaller diesels. I think the weekend drivers oughta listen more and speak
>lots less about the driver's world. John T
>----- Original Message -----
>From: "Joe Garrett" <j.garrett@verizon.net>
>To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
>Sent: Tuesday, November 09, 2004 12:02 AM
>Subject: Re: [MV] M35 Exhaust Brake installation
>
>
> > Actually the policy on downshifting was "don't".
> >
> > Joe Garrett
> >
> >
> > -----Original Message-----
> > From: m35products [mailto:m35prod@optonline.net]
> > Sent: Monday, November 08, 2004 8:51 PM
> > To: Joe Garrett; Military Vehicles Mailing List
> > Subject: Re: [MV] M35 Exhaust Brake installation
> >
> >
> > You mean "...a policy about NOT downshifting..." don't you?
> >
> > apb
> >
> >
> > ----- Original Message -----
> > From: "Joe Garrett" <j.garrett@verizon.net>
> > To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
> > Sent: Monday, November 08, 2004 8:53 PM
> > Subject: Re: [MV] M35 Exhaust Brake installation
> >
> >
> > >
> > > When I was driving a bus, my employer had a policy about downshifting
>to
> > > slow down. Brake linings are a lot cheaper than engines. This would
>seem
> > > to apply here, too.
> > >
> > > Joe Garrett
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