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Our Story

Long steep downhill grades not only provide anxious moments for truck drivers, but they also add extra hours behind the wheel. The advent of the Jake Brake compression release Engine Brake brought an opportunity to end this fear almost entirely and at the same time to safely raise average speeds.

Although the Jacobs Engine Brake has been on the market since 1961, the need for it was terrifyingly demonstrated to its inventor Clessie L. Cummins, some thirty years earlier.  In August of 1931, himself, Ford Moyer, and Dave Evans driving a Cummins diesel powered Indiana truck from New York to Los Angeles attempted to set a new truck speed record across the continent.  All went reasonably well until the descent of the Cajon Pass, on old U.S. 66 leading into San Bernardino, California.  A long, winding and steep gravel road, criss-crossed by a busy mainline railroad, almost led to the demise of the truck, its driver Clessie L. Cummins, and a frantic crew.  In Clessies words:

“About dusk on the fifth day, we reached the top of Cajon Pass west of Barstow, California.  Before retiring to the sleeping compartment, Dave had warned me against this thirty-five-mile stretch of mountainous downgrade.  I failed to register when the sign for the Cajon Pass appeared.  Soon, however, I realized my error.  The brakes wouldn't hold.  Now running in third gear, I tried desperately to get into a lower speed.  Nothing doing, I saw I would just have to ride it out.  I suddenly saw something moving across the road ahead.  I realized with new alarm that a freight train was cutting across our path.  As we raced inexorably toward the crossing and doom, the trains caboose loomed out of the darkness.  Its red lights cleared the highway just as we reached the tracks.  We had escaped certain death by inches.”

The memory of the dark night was never forgotten, and one of its drivers vowed someday to make his engine work when going downhill just as well as going uphill.

Twenty-four years later, in 1955, in retirement in Sausalito, California, Clessie began studying what might be done to turn his engine into an effective “brake.”

An idea for a practical method came to Clessie in 1957 while in Phoenix Arizona.  The idea that hit Clessie revolved around taking advantage of perfectly timed motion already built into Cummins and Detroit Diesel engines; these engines have a third cam on the main camshaft that activates the fuel injector of each cylinder.  A simple retrofit mechanism should be able to transfer this motion to open the exhaust valve.  An important subtlety of the invention made it novel enough that a very broad patent was ultimately granted, affording strong patent protection dating from the time of its application at the U.S. Patent Office.

The vehicle selected for the first field tests of the completed device was a 1955 GMC “Suburban” station wagon re-powered with a Cummins JN-6 diesel engine.  The engine had a displacement of 401 cubic inches and was rated at 125 BHP at 2,500 rpm.  But since the major market potential was in the Cummins NH series diesels at that time, the engine brake mechanism was scaled up and adapted to a Cummins NHRS supercharged model of 300BHP at 2,100 rpm.  The chief reason for selecting this model was simply because a pair of these diesel engines were installed in Clessies 96-foot yacht Canim based in Sausalito harbor.

Although the principles were proved by mechanically transferring the injector motion, a more practical method was to use a fully hydraulic motion and force transfer.  The first retarder housings of the prototype design were  installed on a Cummins diesel engine in a truck owned and operated by the Sheldon Oil Company.  The initial run with the engine brake was to one of their plants just at the eastern base of the grade, down the Sierras on U.S. Highway 50 near Lake Tahoe. Bill Hill, an eighteen-year veteran driver for Sheldon said he normally was forced to pass the turnoff on the job site because of faded brakes; he would come back when he could slow down enough to turn around!  With the engine brake the turnoff was easily made, and the brake drums were barely warm to the touch.  Bill said he never wanted to drive a truck again unless it was equipped with Clessie Cummins new invention.

As a result of prior contractual arrangement, Clessie was obligated to show his ideas first to Cummins Engine Company.  The novelty of the idea, which broke into untried mechanical areas, plus the uncertainty of its commercial merit caused it to be rejected by Cummins Engine Company.  Nonetheless, Clessie was not discouraged, because he also was thinking about starting a small company to manufacture the brake himself.

Clessiess brother Deloss Cummins, once service manager of Cummins Engine Company, lived in Phoenix, where he and a partner ran a successful Cummins engine distributorship.  He visited Clessie occasionally in Sausalito and knew of the ongoing “basement” activities.  Deloss son Don was serving in the U.S. Coast Guard, with one of his last stations being in New London, Connecticut.  The Cummins Engine company distributor in nearby Hartford was a good friend of Deloss and had known Don for years.  This resulted in an invitation to Don to come to Hartford; naturally the visit would be more pleasant if Don could also spend some time there with a person more his age.  Thus a blind date with the daughter of a good friend was arranged.  The girls father, Bob Englund, also happened to be a Vice President of Jacobs Manufacturing Company, the world's leading manufacturer of drill chucks.  There was a natural attraction between Don Cummins and Roberta Englund, and in due course wedding bells were heard.

Don knew through his dad that Uncle Clessie was working on some kind of engine brake, and the word eventually reached the ears of Jacobs Manufacturing Companys President Louis Stoner.  Just weeks before the Sheldon Oil Company test began, a letter was received in Sausalito asking if the Mr. Stoner could come to California to see what invention Clessie had under development.  A demonstration of the brake on the boat engine during a yacht ride on San Francisco Bay, excited the visitors to the point that agreement was soon reached to build brake assemblies for ten engines as quickly as possible from drawings that Clessie's son Lyle provided.  Consolidated Freightways, Pacific Intermountain Express, Willig, Sheldon, Q-N-C, and other trucking firms kindly furnished the trucks.  While several minor problems appeared, the tests demonstrated conclusively the engine brakes improved, safer operation, as well as a large potential cost savings in brake linings and drums.

In April of 1960, Jacobs Mfg. Company made the decision to establish its new Clessie L. Cummins Division, (now named Jacobs Vehicle Systems) for the manufacture of the engine brake.  The first production units for the Cummins NH series engines left the factory in 1961, followed shortly by a brake for the Detroit 71 series.

Clessie Cummins idea for making a diesel engine work downhill as well as uphill has thus been implemented.  The Jake Brake engine brake has become a major contributor to greater control and safer operation of heavy trucks worldwide.  The Jacobs Engine Brake is the 108th National Historic Mechanical Engineering Landmark designated since the program began in 1973, representing a progressive step in the evolution of mechanical engineering, and an influence on society.

Over 50 years later, the same basic principles of varying the engine exhaust valve timing for engine braking are in use in nearly all over the road heavy-duty trucks. And Jacobs remains the leader, providing the highest quality, highest performance engine brakes on the market.

This text is based on an article by The American Society of Mechanical Engineers, 345 East 47th Street, New York, NY, 10017


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