This guy says I am correct on my braking technique. I would say he knows what he's talking about and has more experience and knowledge about braking techniques.
http://www.johncglennon.com/papers.cfm?PaperID=36
Downhill Braking
John C. Glennon, Jr., BSAT
[ Reprinted from the Trucker's World Magazine, Volume 5, Issue 6, June 2001]
When the Commercial Drivers License (CDL) manual was first published, it recommended that a driver use a light and steady application of the brakes when descending steep grades. This recommendation was based on an old theory that heavy brake applications would generate more heat than light applications. This method (controlled braking) was commonly taught to drivers and, even after changes were made to the CDL manual because this theory was proven wrong, the method is still taught and practiced today.
Snub braking is now the recommended method of downhill braking. This method works by: first, choosing the correct gear for the hill; second, allowing the truck to speed up to the maximum safe speed as it descends the hill; third, applying the brakes hard to slow the truck down 5 mph; and then repeating this process to the bottom of the hill. To understand why this method is recommended takes some understanding of the basics about how brakes work. Slowing a truck with it.s brakes, creates friction between the brake shoes and brake drum to convert the kinetic (forward movement) energy of the truck into heat energy dissipated by the brakes. The amount of heat energy produced is dependent upon the weight of the truck and the amount of slowing desired. Assuming these two factors remain constant, the manner in which the brakes are applied, hard for a short time or lightly for a long time, will not change the amount of heat energy and heat produced by the brakes. This heat energy will be distributed among all the brakes that are working. Again, assuming all other factors constant, the more brakes the system has working the cooler each brake will be.
This explains why the old theory of light and steady braking is incorrect. However, to understand why snub braking is the recommended practice, you must also understand the basics of pneumatic balance. Trucks have relay valves to control the application and release of the air brakes. A standard truck-trailer usually has one relay valve for the tractor drive axles and one for the trailer axles. The relay valves are controlled by air pressure from the foot valve (brake pedal). This control pressure opens the relay valve allowing the desired amount of air pressure from the air tanks to pass through the valve and supply pressure to the brakes. Pneumatic balance is created by having equal air pressure at all wheel ends. Pneumatic imbalance is a result of these valves that open at different pressures. For example, a tractor may be setup with a relay valve that opens at 15psi (15psi crack pressure relay valve) and the trailer being towed may have a relay valve with a 3psi crack pressure. A vehicle setup this way would only apply the trailer brakes during controlled brake application, which typically has an application pressure of less than 10psi. However, a .snub. brake application of 20 to 30psi will open all valves and apply all brakes. This type of imbalance can also be a result of contaminants and alcohol in the air system that can cause these valves to hang-up and have higher than normal crack pressures.
Snub braking became the recommended method of downhill braking as a result of testing done by University of Michigan Transportation Research Institute. This research found that trucks with properly balanced brake systems had basically the same average brake temperature when using either the controlled or snub braking method. However, trucks with poor brake balance were found to have more uniform brake temperatures when the snub method was used. Unless pneumatic testing is performed on a truck to ensure that proper brake balance is maintained, there is no way to know if a truck has good brake balance. This type of testing is difficult to perform in most trucking operations since a tractor is usually hooked to several trailers over relatively short time periods. Therefore, for the purposes of deciding which braking method to use, it would be virtually impossible to determine if a truck has good brake balance. This is why snub braking is the recommended method.
Although snub braking does compensate for imbalances in the pneumatic system of the brakes, there is a misconception that snub braking also compensates for brakes that are not evenly adjusted. Brakes that are not evenly adjusted have a torque imbalance. Torque balance is created by having matched mechanical components that are working properly and adjusted correctly. Snub braking has limited ability to compensate for torque imbalance. A good example of this would be a truck with a six-inch slack adjuster on one side of the axle and a five-inch slack adjuster on the other side. This truck will always have an imbalance at any pressure because the brake with the six- inch slack adjuster has more leverage. The same imbalance can happen with uneven brake adjustment because the force output of a brake chamber is directly related to the brake adjustment (push rod stroke).
Since the snub braking method cannot compensate for torque imbalance, trucks should always be inspected and repaired with the following in mind. A truck.s brake system should have matched mechanical components such as the same size brake chambers and same length slack adjusters on both sides of an axle and, most of the time, on all brakes in a group of axles (i.e. tractor drive axles). When inspecting the condition of the brakes, any isolated premature wear found is an indication of a balance problem. If one brake wears faster than the rest, there is a torque balance problem and that brake is doing more work than the rest. If one brake wears much slower than the rest then that brake is not working as hard as the rest. When brakes are repaired, it is important that the cause of an identified torque imbalance be found before repairs are made. Repairs made without correcting the torque imbalance could amplify the problem causing the overworked brake to work even harder. It is equally important to ensure that the same repairs are done on both sides of an axle. If the brake hardware is replaced on the right side of an axle it should also be replaced on the left side. If the s-cam bushings are replaced on the right side they should be replaced on the left.
Snub braking is the method that every truck driver should be using. Although snubbing is a very good precautionary measure, it is still no substitute for a properly balanced brake system. Brake imbalances not only cause brakes to overheat when driving in the mountains, but also can cause instability both on slick driving surfaces and during hard brake applications. These stability problems (to be discussed in a future article) are the primary cause of jackknifes and trailer swingouts. Therefore, I recommend not only that trucks be tested, repaired, and maintained to ensure that they have good brake balance, but also that the snub braking method be used to compensate for any variances that result from interchanging tractors and trailers.
About the Author
John C. Glennon, Jr., is an automotive technologist who performs accident investigation, detailed vehicle testing, and accident reconstruction for insurance companies and lawyers involved in investigating and litigating motor vehicle collisions. He has a B.S.A.T. degree in Automotive Technology, he is a triple-certified Master Automotive Technician, and he holds a Class A CDL in the state of Kansas.
RESUME OF JOHN C. GLENNON, JR.
John C. Glennon Jr., BSAT, Automotive Expert
www.johncglennon.com/automotiveexpert.cfm - [Cached]
Published on: 1/1/2005 Last Visited: 11/11/2006
Resume of John C. Glennon Jr.
Crash Reconstruction
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John C. Glennon, Jr. John C. Glennon, Jr., Automotive Technologist John C. Glennon, Chartered
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John C. Glennon, Jr. is an automotive technologist. His professional capabilities include the investigation and reconstruction of motor-vehicle accidents with special emphasis on the mechanical aspects of large trucks. He can analyze motor carrier safety and compliance, analyze hours-of-service compliance, diagnose mechanical and brake failures, locate previous body and structural damage, determine if proper maintenance and repair procedures were followed, and analyze seat-belt, air-bag, and seat-back failures.
Mr. Glennon has a vast knowledge of motor vehicles that he has obtained from personal, professional, and educational experiences. All of Mr. Glennon's formal education was obtained from Pittsburg State University, which is an internationally recognized school of Automotive Technology and home of the thirty-three million dollar Kansas Technology Center. While attending Pittsburg State University, Mr. Glennon was recognized as the only student ever to have successfully completed all three of the Automotive Programs offered by Pittsburg State. His experience covers all areas of collision repair and mechanical diagnosis and repair of passenger vehicles, large trucks, heavy equipment, and motorcycles. Other areas of experience include customizing of racing and recreational vehicles, and operating and racing motorcycles, boats, and personal watercraft.
Mr. Glennon is a Certified Master Automotive Technician, a Certified Master Heavy-Duty Truck Technician, a Certified Master Autobody Technician, and a licensed commercial vehicle driver. He is a member of the Society of Automotive Engineers, National Academy of Forensic Engineers, Tire Industry Association, and the Midwest Association of Technical Accident Investigators.
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1992 to present - Consultant/Accident Investigator, John C. Glennon, Chartered
Mr. Glennon has extensive experience with accident investigation and the analysis of accident causation for automobile, large truck, motorcycle, and pedestrian accidents. His experience includes analysis and testing of: vehicle components and systems; combination vehicle (truck-trailer) compatibility and stability during heavy braking; and brake pressure and torque balance.
Mr. Glennon's accident reconstruction experience includes analysis of vehicle speeds, direction of travel, and angle of impact using proven accident reconstruction techniques. He also focuses on the investigation of motor-carrier compliance with safety regulations including: maintenance, inspection and equipment requirements of commercial motor vehicles; driver qualifications and knowledge requirements; and driver hours of service requirements.
Mr. Glennon has experience with both deposition and court testimony. He has worked on cases and for clients in the following states: AR, AZ, CA, CO, CT, DC, FL, IL, IN, IA, KS, KY, LA, MD, MI, MN, MO, NE, NC, NM, NY, OH, OK, PA, SC, SD, TN, TX, UT, WA, WI, WV.
John C. Glennon, Chartered is an authorized Private Motor Carrier. Mr. Glennon is the primary individual responsible for the management of the vehicle maintenance, safety, and compliance with Federal Motor Carrier Safety Regulations.
1998 to 2000 - Heavy Duty Truck Technician, Kansas City On-Site Fleet Service
Mr. Glennon worked as a flat-rate technician responsible for performing mechanical diagnosis, repair, and inspections of commercial fleet vehicles. He has performed diagnosis, repair and inspections on various types of vehicles including Freightliner, GMC, Ford, UD Nissan Diesel, Isuzu, Grumman Olson, Utilimaster, and GMC school buses.
1994 to 1995 - Autobody Technician, Royal Motors (A GM and Chrysler Dealer)
Mr. Glennon was an auto-body technician responsible for performing collision and paint repair. His experience consisted of performing both structural and non-structural body repairs of most makes of passenger vehicles and light trucks. Additional experience includes performing warranty and recall repairs on GM and Chrysler products.
1991 - Automotive Service Aide, Vee Village Auto Service
This position was a summer internship, which provided experience in a wide variety of automotive service areas. Mr. Glennon's responsibilities included assisting both the shop manager and the technicians during the shop?s peak season. Specific duties included: writing repair orders, assisting technicians with repairs, locating and delivering needed parts and performing light repair work.
RELATED EXPERIENCE In addition to Mr. Glennon's experience as an automotive and auto-body technician, he also has experience building and modifying vehicles for racing and recreational purposes (i.e. street rods, boats, etc.). He has performed various frame and suspension modifications, running gear changes, custom transmission rebuilds, and engine performance. He has also fabricated roll cages for race cars, modified and reconfigured electronic fuel management systems, raked and stretched motorcycle frames, and modified boat and jet ski engines and hulls.
Mr. Glennon's experience modifying frames and suspension systems includes narrowing or "tubing" the rear frame section in order to accommodate larger rear tires for racing purposes, lowering vehicles in order to increase handling performance, lifting four-wheel drive vehicles, designing and fabricating custom parts for a race-car suspension system, and aligning vehicles to optimize desired handling characteristics.
Mr. Glennon has performed numerous repower projects, which include fabricating special parts and modifying the vehicle in order to replace the stock engine with a larger one. This normally involves building vehicles such as street rods and racecars.
Mr. Glennon has many years of experience riding and racing motorcycles, operating racing cars, riding and racing jet skis, and driving racing boats. He has also conducted acceleration and top speed testing of personal watercraft and boats.
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[ A collection of Mr. Glennon's articles is available at Criterion Press ]
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© 1998-2006 John C. Glennon, Chartered. All rights are reserved.
2. Solomon, Saltsman & Jamieson | Radio Show
www.ssjlaw.com/radio.htm - [Cached]
Published on: 5/15/2001 Last Visited: 11/6/2001
July 7 , 2001 -- Killer Products ; defective tires and defective tires and defective baby products and toys with Ken Giles , US Consumer Product Saftey Commission and John Glennon Jr. , Automotive Technologist.
3. Solomon, Saltsman & Jamieson | Radio Show
ssjlaw.lawoffice.com/radio-archive-2001.htm - [Cached]
Published on: 1/6/2001 Last Visited: 5/31/2003
July 7, 2001 -- "Killer Products; defective tires and defective tires and defective baby products and toys" with Ken Giles, US Consumer Product Saftey Commission and John Glennon Jr., Automotive Technologist.
I drive 125 on regular road and on mountain you drive a little slower,yes? :?
