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Braking while descending steep grade

Yahoo Message Number: 86394
There has been extended discussion recently regarding Exhaust (PAC) and engine (Jake) brakes.
One poster commented regarding the application of the brakes "...apply lightly to avoid over heating." I too had read this many years ago and was laboring under the same out-dated misconception. No offense to the writer as this is a fairly common notion.
This method has since been refuted. The proper way to slow down is of course with the engine or exhaust braking system until you reach equilibrium of braking vs speed. However, if the combination of weight and engine or exhaust braking exceeds the capability of your system causing the speed to climb, apply brakes firmly for a few seconds until you reach a safe speed then release. The truckers refer to this as "snubbing" the brakes.
The California DMV Commercial Drivers Handbook for 2012-13 does not advise light pressure over an extended period.
I have reversed my thinking on the "light pressure" method that I was previously applying. I will test this "snubbing" method on my next trip from Southern Ca to OR and WA this Summer. My route includes several 6% and 7% grades. As a matter of fact, one grade on a back country, two lane road leading from CA Hwy 50, Shingle Springs to a campsite in Lotus, CA has a hair-raising 10% grade over a three or four mile stretch down to the American River valley.
For those who are interested in the documentation, I googled the subject and uncovered a reprint of an article from "Truckers World" magazine, Vol 5, issue six, June 2001. I found this extensive discussion in a bus conversion website under "Proper way to descend a grade".
Google www.busconversions.com/bbs/indexphp/topic=5366.15
BTW, the PAC Brake up-grade was an excellent investment. Performance is great, especially at lower RPMs! Have fun, drive safe,

Daron Hairabedian, 98 Allure, 30226 with up-graded PAC Brake, towing Chev Malibu.

Re: Braking while descending steep grade

Reply #1 –
Yahoo Message Number: 86397
What is the difference between an exhaust break, engine break and a jake break? While traveling in Texas I see many signs when entering towns and cities posting "engine breaks prohibited" or something like that.

Walt

Re: Braking while descending steep grade

Reply #2 –
Yahoo Message Number: 86400
Walt

An exhaust brake is valve device mounted where the exhaust manifold joins the exhaust pipe. When the driver removes his foot from the throttle the valve closes thus restricting the exhaust. This applies back pressure on the engine providing some braking from the engine. Diesel engines, because of their inherent design, do not provide as much engine braking as gas engines.
An engine brake is just another method of achieving the same result. Here a hydraulic device is added to the header that prevents the exhaust valves from opening until just before top dead center. This basically turns the engine into big compressor compressing against itself. This provides a lot of engine braking. The characteristic popping noise happens when the exhaust valves release the compressed exhaust gases.
It is really the engine brake that the signs are targeting particularly the large trucks that have straight pipes with no mufflers. The exhaust brake only emits a hissing sort of sound that is not very loud.
So the technical name for the two types are exhaust brake and engine brake. Sometimes you will see the word compression thrown in between engine and brake. The term Pac Brake is a brand name that over time has come to be used to identify exhaust brakes. Likewise Jake is a brand name of engine brake.
The term two stage or three stage applies only to engine brakes. It refers to the ability to select the number of cylinders being used for compression braking . My 375 hp Cummins had a 2 stage engine brake. In the low range only three of the six cylinders were used while in high all six were used. The more cylinders the more braking. Engine braking is more positive than the exhaust braking but still the exhaust is a big help. Some engine manufactures limit the size engine that they will factory install engine brakes. At the time when I bought my 2004 Allure the ISL was the smallest block that Cummins supplied with engine brakes. Of course that was 12 years ago and times change. Also retro-kits are available for even pickup trucks

Don Seager

Former CC Owner

Walt Leutwyler wrote:

What is the difference between an exhaust break, engine break and a jake break? While traveling in Texas I see many signs when entering towns and cities posting "engine breaks prohibited" or something like that.

Walt

Re: Braking while descending steep grade

Reply #3 –
Yahoo Message Number: 86407
Don,

As always, another one of Don Seager's great posts. Very clear and well written!
Walt, the only minor detail that I may add is that the moniker, "Jake" has evolved from the manufacturer's name. The full company name is "Jacobs Vehicle Systems". They seem to be the leader in engine valve system braking. Also, Pac Brake has become so popular that their name has become more or less synonymous with exhaust brakes.

Daron Hairabedian, 98 Allure, 30226

 

Re: Braking while descending steep grade

Reply #4 –
Yahoo Message Number: 86411
Great explanation as to the distinction, Don. And what you say gybes with my own manual and information... Our CC has the 9.3L CAT 9 wuth three stage engine braking. The manual is very illuminating on the topic so I copied and pasted the info here:
http://www. Wind-seeker.com/tech/engine-braking.html
Don, I also addded your explanation at the bottom as a reprint from the forum... hope you don't mind but it may be useful to have all the info in one place on this often misquoted subject.

Joseph Burkle

2008 Country Coach Inspire 360 Founders Edition 43' quad slide tag axle 425 HP C9 pusher http://www. Wind-seeker.com/