These Devices Provided Added Stopping Ability in Hilly Terrain and Added Control on Flat Land Or City Streets, While Also Enhancing Brake Lining and Tire Life

Home , Exhaust brake

These devices provided added stopping ability in hilly terrain and added control on flat land or city streets, while also enhancing brake lining and tire life.

By CAROL F MAXWELL & ES. GURDJIAN, F76350

he engine brake, exhaust proved to be unreliable. still in the shortest possible distance brake, transmission retarder, Cummins, et al, had begun re- without loss of control, as in emer- T and electromagnetic drive- search and development of an engine gency stops. Because of design and shaft retarder are four types of acces- brake in 1956. During the same period manufacturing limitations, foundation sory braking devices used in mo- (1954), the Williams Controls, for- brakes cannot effectively dissipate the torhomes today. These systems en- merly known as Willams Air Control, temperatures reached when used re- hance stopping ability in both hilly developed an exhaust brake. They peatedly and for extended periods of and level terrain. An added benefit is experimented with butterfly- and guil- time. The foundation brakes of a 15- that they help to preserve brake linings lotine-type valves and ultimately fo- ton, 4x2 vehicle descending a 12 per and tires. In addition to examining the cused on the guillotine, which is still cent grade, 4.35 miles long, produce workings of these devices, it is inter- in use today. enough energy to melt a 463-pound esting to explore the history of acces- The importance of accessory metal casting. On a 6 percent gradient, sory brakes, which have been in exis- brakes is dramatically demonstrated in the foundation brakes of a 19-ton 4x2 tence for a number of years. data compiled by Telma Retarder Inc. vehicle traveling at 40 mph reach 752 Sarrazin, a French engineer, was The chart below, provided courtesy of degrees Fahrenheit after only 15 sec- granted a patent to use eddy currents Telma, compares brake surface area to onds. The hotter brake linings get, the as a vehicle retarder in 1926. In 1936 weight ratios. The chart indicates that less efficiently they perform (up to 60 Telma purchased the rights to the pat- heavy trucks have almost four times percent loss of efficiency above 520 ent and began producing the Telma less brake friction area per ton than degrees Fahrenheit). It will take the electromagnetic retarder. In August 1961, C. Lyle Cummins Jr. and G.S. Haviland presented a paper titled “The Type of Vehicle Brake Surface (Sq. In.) Weight (Tons) Sq. In./ton Jacobs Engine Brake, A New Concept 2,202 pound car 117 1 117 In Vehicle Retarders” at the Society of 8,900 pound truck 223 4 56 Automotive Engineers (SAE) national 14,500 pound truck 330 65 51 West Coast meeting in Portland, Ore- 37,000 pound truck 750 16.5 45 gon. In this paper, Cummins acknowl- 80,000 pound truck 1,128 36 31 edged that “the concept of retarding a vehicle by converting an engine into some form of air compressor is not cars. above vehicle 15 minutes at 19 mph to new. Patents dating back at least 40 According to the Telma literature, bring the temperature of its brakes years show attempts at this.” These “Foundation brakes are designed to down to 392 degrees Fahrenheit. patents all made use of shifting cam- maintain a vehicle in a stationary posi- “When foundation brakes are ap- shafts and extra cam lobes to change tion for indefinite periods, as in park- plied, heat is generated. This heat ra- exhaust valve timing. All of them ing, and to bring the vehicle to a stand diates to the wheels and eventually to

86 JULY 1996 • FMC sion while obtaining no energy from the power stroke. See Figure 1 for a comparison of what happens without and then with a Jake Brake installed. In Figure 2, titled “How A Jake Brake Works,” note the following components: solenoid, control valve, master piston, slave piston, and exhaust valve bridge (exhaust cross- head). The solenoid can be activated only during a “no fuel” condition. The solenoid allows engine oil to flow through the control valve to the master and slave piston. The master piston is forced down onto the rocker arm of the fuel injector, then the rocker arm pushes the master piston upward. The control valve prevents backflow of the engine oil trapped between the master the tires, which can result in tire blies are controlled by one solenoid, piston and the slave piston. The slave blowouts. Bead temperatures in excess with the second housing assembly piston is pushed downward on the of 250 degrees Fahrenheit for ex- referred to as a drone. The V6 has exhaust valve bridge, opening the extended periods of time cause burnt tire three housings per solenoid; two are haust valves. This allows the com- beads, making remounting operations drones. The eight-cylinder applica- pressed air to escape from the cylinder difficult and tires unfit for retreading. tions have four solenoids that usually through the exhaust system to the at- Heat causes tires to run hotter and wear faster. Retarders reduce tire op- 8V92 Detroit Diesel engines often are equipped with a erating temperatures and increase tire life by more than 10 percent for most dash-mounted dual pyrometer that measures the tempera- effective units.” ture of the gases in both exhaust manifolds. Some con- Engine brake. Historically, the sider this gauge unnecessary, but we have found it to be Jacobs Engine Brake has been very quite valuable. In the event of a Jake Brake malfunction, well received. The Jake Brake, as it is this instrument can help identify the problem known, is ideally suited to large- displacement, heavy-duty diesel engines, although assemblies have to be are wired in pairs, and each pair is mosphere. Figure 3 illustrates this customized for each engine model. activated separately. The six-cylinder process. Engine brakes can produce substan- applications have two solenoids, each The rocker arm of the fuel injector tially more retarding horsepower than individually activated. On straight-six is used to time the opening of the ex- exhaust brakes. In motorhome applica- applications, there are two or three haust valve. Some engines may use tions, the Jake Brake is used on the housings, depending upon engine other means of timing, such as an ex- larger Detroit Diesel engines, includ- type, with one solenoid per housing. haust valve rocker arm of another ing the Series 60. Pacbrake Engine In the most simplistic terms, the cylinder. The engine brake is capable Brakes also produces an engine brake Jake Brake turns the engine into an air of producing a brake horsepower ef- for the Series 60 engine. compressor. During a “no fuel” condi- fect approximately 85 percent of the On V6 and V8 Detroit Diesel two- tion (no fuel injected into the cylin- rated output of the engine. The higher cycle engines, the engine brake con- ders), the exhaust valves are opened the rpm, the higher the efficiency. sists of one housing assembly per cyl- just before the power stroke, so the inder. On the V8, two housing assem- engine does all the work of compres-

86 JULY 1996 • FMC allows the activation of either two or To properly integrate the WTEC four solenoids, which control four or with the DDEC III, the requirements eight cylinders, respectively. On elec- of both Allison Transmission and De- tronic engines, there is a dash module troit Diesel must be met. that connects to a Jake Brake control module. The control module is con- Transmission requirements: nected to the ATEC ECM (Allison • Transmission ECU must be pro- Transmission electronic control, elec- grammed with combined “Engine tronic control module) and the DDEC Brake” and “Preselect Request” plus ECM (Detroit Diesel electronic con- “Engine Brake Enable” (“Preselect” trol, electronic control module). There modifies shift schedule to raise engine is also provision for a clutch switch on rpm for maximum engine brake effec- manual transmissions and a pressure tiveness. The standard preselect is 6-4. switch on some automatic transmis- Some OEMs use 6-5). sions. 8V engines use a high-mode or • Engine brake enable switch in low-mode control. “on” position. Series 60 engines after serial num- • Throttle position signal less than ber 060004455 are Jake Brake ready. 10 percent. Jake Brakes should not be installed on • Transmission must be in lockup. engines with lower serial numbers. Because of space restrictions on some DDEC III requirements for en- coach chassis, a two-housing Jake gine brake operation: Brake kit may be required. In this • Engine brake enable switch in case, only four of the six cylinders “on” position. will be used for the retarding effect. • 0 percent throttle position. These installations will have a two- • Engine must be in “no fuel” con- mode switch — high and low. An in- dition (no fuel injected into cylinders). stallation with three assemblies will • Engine rpm at minimum of 250 have a three-mode switch- high, me- rpm greater than idle rpm. dium, and low. Prevost coaches utilize • If clutch switch input function three housings with a two-mode configured “on,” input must be switch. All six cylinders are activated grounded. in the high mode and four in the low. One of the reasons the Jake Brake On DDEC II applications, a dash has been so well received is its dura- switch and a control module interface bility. The Jake Brake is tuned as part with the DDEC II ECM and the ATEC of a standard engine tune-up and usu- ECM. In addition, there is also an in- ally does not require any additional terface between the engine brake and maintenance. Special tune-up kits are the WABCO antilock braking system available from Jacobs Vehicle Equip- Figure 4 shows the electrical wiring (ABS). On DDEC III applications, the ment Company warehouse distribu- diagram for activation of the solenoid engine brake is controlled by the tors. While the Jake Brake usually is on a mechanical engine. The clutch DDEC III ECM, so no Jacobs control included as original equipment, it also switch is not used for automatic module is required. DDEC III allows can be retrofitted to a coach. A retrofit transmissions. The buffer switch is simultaneous engine brake capability installation would cost between used to determine the “no fuel” condi- and cruise control operation. It also $2,000 and $3,000. This includes ap- tion in Detroit Diesel Series 71 and 92 interfaces with the WABCO ABS and proximately eight hours of installation mechanical engines. On 8V Detroit the World Transmission ECM time. Of course, any modification engines, a two-position dash switch (WTEC). problems would increase the cost.

86 JULY 1996 • FMC Using a pyrometer to monitor Once recognized, you can attempt parity between the left-side and right- engine brake performance. 8V92 to temporarily alleviate the condition side temperatures when the Jake Brake Detroit Diesel engines often are by releasing the accelerator and manu- was activated. It is important to re- equipped with a dash-mounted dual ally turning off the Jake Brake. You member that other conditions, such as pyrometer that measures the tempera- can then try to fuel the engine again injector or linkage problems, may ture of the gases in both exhaust mani- while watching the pyrometer. If the cause changes in the pyrometer read- folds. Some consider this gauge un- pyrometer needles remain equalized, ings. necessary, but we have found it to be the attempt was successful. If the so- Exhaust brake. Initially, exhaust quite valuable. In the event of a Jake lenoid problem persists, you should brake performance was limited by the Brake malfunction, this instrument can seek professional advice as soon as engine manufacturers’ specification help identify the problem. During possible. If one or both Jake Brake for maximum allowable back pressure. normal operation, both indicator nee- solenoids on one side release prema- Exhaust brakes currently supplied on dles will range from a low of 300 de- turely or stop functioning, the tem- small displacement diesel engines grees Fahrenheit under no-load, no- perature on that side will be lower have benefited from engine manufac- fuel conditions, to a high of 1,100 than the opposite side. Not only does turers using valve springs with higher degrees Fahrenheit under full-load, the pyrometer indicate that a problem tensions, which allow greater back fuel conditions. Depending upon how exists, it also indicates which side is pressure. the engine has been tuned, there may malfunctioning. The exhaust brake unit is inserted be a slight but constant variation be- We learned this from our own ex- in the exhaust system just after the tween the left-side and right-side indi- perience with an intermittently stick- turbocharger, and in the case of cators. When the Jake Brake is acti- ing solenoid that presented the condi- Pacbrake is mounted directly to the vated on both sides, the two indicator tions described above. We had asked turbo. The valve body consists of a needles will settle at approximately numerous service personnel what they round chamber containing a butterfly 500 degrees Fahrenheit. If the Jake thought these conditions meant. We or guillotine valve, activated by an air Brake is activated on one side only, were told everything from stuck injec- cylinder, vacuum cylinder, or electric the needle on the corresponding side tors to some sort of turbo problem. No solenoid. The installation kit includes will drop only to between 400 degrees one, however, suggested a sticking two exhaust flanges that are welded to Fahrenheit and 500 degrees Fahren- solenoid. Some said to start replacing the existing exhaust pipe. For after- heit, while the needle on the “off” side parts until the problem was resolved, market installations, a section of the will drop to approximately 300 de- but we were not satisfied with a “hit or existing exhaust pipe is removed and grees Fahrenheit. miss” approach. Ultimately, we iso- the flanges are welded to the cut ends. If a solenoid should stick in the lated the problem by alternately dis- The brake assembly is then held in “on” position, the exhaust valve re- connecting the two solenoids on the place using two exhaust clamps. Each manufacturer has its recommended location for installation. In an air-equipped coach, the valve is activated by an air cylinder that is controlled by an electric air solenoid. In a coach without air, the valve may be activated by a small air compressor or directly by an electric solenoid or vacuum cylinder. The exhaust brake may be activated manually by a foot switch (see Figure 5) or a hand lever. It may also be activated automatically by a fuel pump switch enabled in the “no fuel” condition (see Figure 6). If the coach has a World Transmission, there should be an interface between the exhaust brake and the World Transmission ECM. This interface indicates to the transmission that the mains open during the power stroke. affected bank. One created the high- exhaust brake is activated and directs The pyrometer reflects this condition temperature condition, and the other it to choose one of the predetermined by showing a rapid temperature rise did not. We initially replaced the sole- downshift schedules. on the affected side, which is greatly noid “O” rings, which did not solve Performance is determined by en- disproportional to the normally func- the problem. Subsequent replacement gine rpm and back pressure. It is de- tioning side. You may note a puff of of the malfunctioning solenoid pro- sirable to achieve maximum back black smoke from the exhaust pipe. If duced trouble-free performance. pressure without exceeding manufac- allowed to persist, this condition can On another occasion, we were able turers’ specifications. The various cause serious damage to the exhaust to diagnose a broken wire to one of techniques used to meet these parame- valves. the solenoids because there was a dis- ters include using a back pressure

86 JULY 1996 • FMC gauge and a pressure switch to open the valve when limits are exceeded. Brian Roth of BD Engine Brake re- ports that his company’s kits all con- tain brake pressure gauges and a pressure limiting switch. BD officials have noticed on their gauges that even if heavy-duty valve springs are installed, pressures can exceed their higher specifications. BD has designed a stainless-steel offset butterfly; as engine back pressure climbs, the butterfly gradually opens to maintain high pressure. Thus, the back pressure is the same at 2,000 rpm as at 2,500 rpm. Other methods use a small relief aper- ture specifically sized for the intended engine application, or an adjustment screw to prevent the butterfly valve from closing completely. This screw is adjusted to maximum allowable back pressure. The exhaust brake’s basic assem- (plus a towed car) with only service cracking. Exhaust compression heat bly is adaptable to numerous diesel brakes and have some not-so-fond prevents this sudden cooling.” engines. Smaller engines frequently memories of navigating 8 percent In regard to using an exhaust brake are paired with the Allison World grades as slowly as possible with the without a lockup automatic transmis- Transmission, which can provide a brakes squealing all the way down. sion, King said, “In the design speed sequential downshift from sixth to Decelomatic Corporation has been range of a particular gear, the auto- second or sixth to fourth. This in- installing exhaust brakes since 1968. matic transmission without lock-up is creases the engine rpm to effect The company uses the Williams valve ninety percent to ninety-five percent greater brake horsepower. Perform- for diesel engines, and it manufactures torque efficient. Adding lockup may ance is also maximized by the lockup and installs the “Mountain Tamer,” add up to five percent more torque feature of the torque converter in the the only exhaust brake available for efficiency. The secret is to use the World Transmission. gasoline engines. proper gear for descending. It is also The exhaust brake is usually origi- Some experts believe that a gaso- as important on the ascent. Proper gear nal equipment, but it can be retrofit- line engine, transmission, and drive- selection is required to prevent slip ted. Engine manufacturers will have line components are not strong enough and attendant overheating for both specific recommendations concerning to provide prolonged durability with ascent and descent.” More than 3,000 maximum exhaust pressure and valve the use of accessory braking devices, gas-powered vehicles have been spring tension. Heavy-duty springs are because the maximum allowable back equipped with the Mountain Tamer. available for Cummins B5.9 and C8.3 pressure of a gas engine is signifi- The company policy is to honor any engines only. No spring change is cantly lower than that of most diesel claims of damage to the engine caused required for Caterpillar 3208T, 3116, applications. Louis King, president of by the exhaust brake valve during the and 3126 engines, or for Detroit Die- Decelomatic, responds that, “Exhaust vehicle warranty period. Incredibly, sel 8.2 and the new Series 40 engines. braking is not related to compression King notes that not a single claim has The retrofit cost is approximately ratio but only to the strength of the been submitted. According to King, $1,500, including installation. exhaust valve springs. For instance, a “To provide maximum retarding pres- Exhaust brake manufacturers in- Ford diesel 7.3-liter and a Ford 460- sure with existing exhaust valve clude Pacbrake Manufacturing, Jacobs cid gas engine both have nearly the springs, Decelomatic utilizes a gate Vehicle Equipment Company, BD same exhaust valve spring load and valve to obtain good sealing over a Engine Brake, Decelomatic, U.S. both produce approximately thirty-five long life in the presence of exhaust Gear, and Williams Controls Inc. psi of retarding pressure. A stronger deposits. The gate valve has several Exhaust brake for gasoline en- valve spring is available for the gas features. It provides one hundred per- gines. The Telma chart showing the engine for racing applications but is cent removal of the closure from the ratio of brake surface area to vehicle very rarely needed or used for added exhaust flow path, thereby assuring weight indicates that a 14,500-pound retarding capacity.” King continued, zero pressure loss. It provides inherent vehicle has half the braking surface “Gasoline exhaust systems are de- self-cleaning of the sealing surface. It area per ton as compared to a car. We signed for over 100 psi backfire pres- can be simply designed to fail open to take this to indicate that even small sure. The hardest thing on an exhaust assure continued vehicle operation. It Class A motorhornes will benefit from system is sudden cooling from a high- can be one hundred percent enclosed an accessory braking device. We have heat condition causing warping and to protect working parts from road driven a 16,000-pound motorhome

86 JULY 1996 • FMC grime, sand, dust, mud, and salt. To shaft and rotates at Figure 9, provides automatic operation obtain maximum supplemental brak- the speed of the shaft. The rotor of the to a predetermined level of retardation ing from the Mountain Tamer, an op- input retarder rotates at engine speed. when the engine is in a “no fuel” con- tional shift kit can be installed in the The rotor of the output retarder rotates dition. automatic transmission. This permits a at driveshaft speed. The rotor, the re- The Allison World Transmission manual shift from three to one at any tarder housing, and the stator are (WT) series can be equipped only with speed, which has the capacity for a vaned. (See figures 7 and 8.) the output retarder. It also has an ac- real neck-popping deceleration with- The valve body controls the flow cumulator to maintain a reserve out overrevving the engine. This is of transmission fluid in and out of the amount of transmission fluid for called our Drop Anchor kit and retails retarder. To initiate the retarding proc- quickly filling the retarder housing. for approximately three-hundred-fifty ess, transmission fluid fills the stator (See Figures 10 and 11.) The output dollars. Another popular optional fea- and retarder housing. The rotor vanes retarder functions similarly to the in- ture is the variable braking control. move the fluid while the stationary put retarder. Its rotor is splined to the This enables the driver to “tune in” the vanes of the stator and retarder hous- output shaft and always rotates at downhill speed to match the traffic ing resist the motion. This action cre- drive-shaft speed. Retarder capacities flow.” Exhaust brakes for gasoline ates friction and heat as it slows the are shown below: engines appear to be effective and do rotor and shaft. The heat is dissipated The retarder electronic controls in- not seem to be associated with engine via the transmission fluid as it circu- clude the ECU, a resistance module, component failures. The exhaust brake lates through the transmission cooling two solenoids, and a retarder tempera- valve requires some maintenance at system. To stop retardation, the trans- ture sensor. The ECU controls all the engine oil change intervals. With the mission fluid is allowed to flow out of functions of the transmission and the elimination of lead in gasoline and the retarder housing and the rotor retarder. The resistance module con- with today’s cleaner-burning fuels, moves freely. verts a signal generated by the retarder exhaust contamination problems have The Allison HT 700 Series offers apply device into a signal that the lessened. The valve(s) can be installed either an input or output retarder. It is ECU can recognize. One of the sole- on pre-electronic engines with case. not possible to equip a transmission noids controls application of vehicle When installing an exhaust brake on a with both retarders simultaneously. air pressure to the accumulator, and post-1989 gasoline engine, it is impor- The input retarder is particularly well- the second controls the retarder con- tant to maintain engine computer and suited for vehicle downhill speed control regulator valve. The retarder tem- emission standards integrity, The total trol, and the output retarder is particu- perature sensor sends retarder tem- cost of adding a Decelomatic Moun- larly well-suited for stop-start duty perature information to the ECU. tain Tamer to a gasoline engine is ap- cycles. Either retarder significantly There are two versions of software to proximately $3,000. increases the heat load, and any vehi- handle over-temperature conditions. Transmission retarder. The basic cle with a retarder must have an up- Inputs to the ECU include retarder components of a transmission retarder graded transmission cooling system to enable, service brake status, and anti- are the rotor, stator, retarder housing, achieve satisfactory heat dissipation. lock brake response. These inputs, and control valve body. The orienta- A hand lever, foot switch, or a combi- along with numerous others, are used tion of these components to the trans- nation hand lever and pneumatic con- for adaptive shift logic in the ECU to mission will determine whether it is an trol are available options for activating continuously optimize shift quality. “input” or “output” retarder. The rotor the valve body to initiate retardation. Outputs from the ECU are retarder is splined to either the input or output The combination control, shown in indicator and retarder temperature

86 JULY 1996 • FMC indicator. There are several methods of activating the WT output retarder. A hand lever or foot pedal can be set at different positions that send a varied 5-volt signal to the ECU. The ECU interprets this signal and determines the level of retardation. The hand lever is a six-position lever that allows adjustment from zero to 100 percent retarding capacity. This feature provides a flexibility that many motorhome owners find desirable. A “Pressure Switch” option inte- grates retarder activation with the vehicle service brakes. Up to three switches can be connected to the service brake system to provide one to three distinct levels of retardation. All switches are normally open and close

dependent on the switch’s calibration. They are available in four different RETARDER CAPACITIES pressure settings (2, 4, 7. and 10 psi) WT retarders are available in three different capacities: low, medium, and and are non-adjustable. high. Maximum retarder capacity is determined by the spring under the re- The “Auto Apply” option has two tarder control valve located in the retarder control valve body. capabilities. The “Auto Full On” option allows the ECU to command the MD retarders are capable of absorbing the following torque and horsepower retarder “Full On” when the “Retarder output: Enable” switch is activated and the Capacity Power Torque throttle is closed with the transmission output speed above a preset value. The Low 298 kw (400 hp) 1.356 Nm (1,100 lb ft) “Auto Half On” is the same as “Auto Medium 373 kw (500 hp) 1,898 Nm (1,300 lb. Ft) Full On,” except the ECU commands High 447 kw (600 hp) 2,170 Nm (1,600 lb ft) the retarder “Half On.” “Auto Half On” is available only in combination HD retarders are capable of absorbing the following torque and horsepower with another control device that pro- output: vides for “Full On” capabilities. Capacity Power Torque Any two of the previously men- Low 373 kw (500 hp) 1.763 Nm (1,300 lb ft) tioned retarder apply controls can be Medium 447 kw (600 hp) 2,170 Nm (1,600 lb ft) installed in the same vehicle. A com- High 447 kw (600 hp) 2712 Nm (2,000 lb ft) bination of controls allows greater flexibility in applying the retarder. The transmission retarder is compati-

86 JULY 1996 • FMC ble with antilock braking systems Electromagnetic retarder. Telma is the world leader in electromagnetic retarders. Figure 12 illustrates the components of the Telma retarder. It has two rotors and a stator, with the rotors separated from the stator by small air gaps. The stator contains eight electromagnetic coils that are activated in pairs to allow four stages of retardation. Telma manufactures models that can be installed in a mid- driveline location or as an integral part of the transmission or drive axle assembly. Figure 13 shows a Telma- equipped RS-24-160 axle. Electrical current flowing through the stator coils produces magnetic fields of alternate polarities. As the rotors pass through these fields, eddy currents are generated. The currents slow the rotors, the attached driveshaft(s), and the drive wheels. There is no friction on the moving parts, braking loads are not carried by the clutch/transmission internal components, and the heat generated during braking is self-dissipated by the rotors as they rotate. The degree of retardation is not affected by speed, engine rpm, or type of transmission. The effect is also the same regardless of whether the transmission has a lockup torque converter. The Telma retarder is extremely powerful with brake horsepower be- Telma has an extensive product of water weigh 450 pounds. tween 130 and 1,170 depending on the line to precisely match the retarding The Telma retarder can be con- retarder. Its operation is quiet, with needs of each application. This in- trolled with either a hand control, full activation within 120 milliseconds cludes vehicles ranging between 6,000 brake pedal, or both. As mentioned of retarder control activation. Full and 100,000 pounds. The retarder earlier, retardation occurs in four deactivation occurs within 120 units weigh between 137 and 700 stages, and full retardation is achieved milliseconds to avoid parasitic loading pounds. Retarders for motorhome ap- before service brakes are applied. A to the vehicle during acceleration or dashboard display of four lights indi- Accessory braking devices greatly improve vehicle cates the level of retardation. An automatic switch disengages the re- safety. Reliability and durability of service brakes are in- tarder when the vehicle comes to a stop. creased, and maintenance dollars are saved by increas- We had the opportunity to drive a highway coach equipped with a Telma ing the life of brake linings and tires. Anyone who has retarder and were favorably impressed with its performance. The Telma is driven a motorhome equipped with an accessory brake used in a variety of applications, including long-haul trucks, transit buses, is not likely to give up this option willingly. ambulances, fire trucks, and refuse trucks. It can he used with either diesel or gasoline engines and can be retrofitted. Precise alignment of the drive the vehicle during acceleration or plications usually weigh between 300 shaft is critical, so it must be installed coasting and to avoid any interference and 500 pounds. To keep weight in by an authorized service center. Since with the proper functioning of antilock perspective, remember that 50 gallons there is no friction or moving parts, braking systems.

86 JULY 1996 • FMC the only maintenance is bearing lubri- In today’s market, many diesel- Decelomatic Inc. cation every 24,000 miles. The capac- powered motorhomes come equipped 4837 Indian School Road ity of the vehicle’s electrical system with an accessory braking device. Phoenix, AZ 85018 may have to be increased by upgrad- Those that are not so equipped can be (602) 956-8200 ing to a high-output alternator or up- retrofitted. Louis King grading the batteries. The cost of ret- rofitting a Telma retarder is between Any retrofit must be carefully Jacobs Vehicle Equipment $4,000 and $6,000. planned considering the recommenda- Company Summary. Accessory braking de- tions of the engine and transmission 22 E. Dudley Town Road vices greatly improve vehicle safety. manufacturers. The consumer should Bloomfield, CT 06002 Reliability and durability of service have thorough knowledge of the com- (203) 243-7635 brakes are increased, and maintenance ponent manufacturers’ warranty and Bill Werner and David Pearman dollars are saved by increasing the life who is responsible should any damage of brake linings and tires. Anyone who occur to the transmission, engine, or Martin Diesel Inc. has driven a motorhome equipped driveline components. P.O. Box 1000 with an accessory brake is not likely to Further Info Defiance, OH 43512 give up this option willingly. While The following companies and in- (419) 782-9911 other coaches plunge down the moun- dividuals provided information and/or Jim Martin tainside at frightening speeds, those illustrations for this article: with an accessory brake tame the Pacbrake Engine Brakes treacherous terrain. Even on flat land Allison Transmission P.O. Box 1822 or city streets, the device improves P.O. Box 894 250 H St. control by increasing the available Indianapolis, IN 46206-0894 Blame, WA 98231 -1 822 braking ability. (800) 252-5283 (800) 663-0096 David Wheatley Bruce Sebring and Kevin McKilligan

BD Engine Brake Telma Retarder Inc. Unit AlO, 33733 King Road 3488 Diablo Ave. Abbottsford, British Columbia Hayward CA 94545 Canada V2S 4N2 (510) 784-1048 (604) 853-6096 Tell Adams Brian Roth

86 JULY 1996 • FMC