SERVICE MANUALTrailer Charge (Fig. 7)If both valves are out, parking the combinationvehicle, and it is desired to recharge the trailer leavingthe tractor spring brakes applied, the red knob may bepushed in repressurizing the trailer supply line. Thismode may alsobe used to park a combination vehiclewith tractor spring brakes only.Automatic ApplicationWith both knobs in, as in the normal run position(Fig. 8 ), and supply pressure to the push-pull valves isreduced to 276 27.6 kPa (40 5 psi), the red knob(trailer supply valve) must pop out, applying theemergency or parking brakes on the trailer. If the redknob is held in manually and the pressure decreases to207 27.6 kPa (30 5 psi), a tripper piston within thetrailer control spool will move upward, exhausting thetrailer air supply, thus applying the trailer brakes.Fig. 8 Normal Operating PositionNormal Run Position (Fig. 8)With both knobs pushed in, air is now being supplied tothe trailer and to the tractor spring brakes; all brakes arereleased.Actuation or Trailer Park or Emergency Brakes (Fig.9)To actuate the trailer brakes only, the red knob ispulled out, exhausting the trailer supply line. The trailerbrakes are now applied either by emergency air or springbrakes, depending on the type of trailer system. Thismode would be used to uncouple from the trailer andduring bob-tail operation.Fig. 9 Park Trailer with Tractor Released or BobtailTractorMAINTENANCEOnce each year or every 160,000 km (100,000miles) the modular control valve should be disassembledand thoroughly cleaned. Replace all componentssupplied with the repair kit.Lubricate all components with lubricant listed inLUBRICANT SPECIFICATIONS, Item 3.Perform the Service Checks after rebuilding valveassembly.SERVICE CHECKSWhen the service checks on the modular controlvalve are performed on the vehicle, both the Leakageand Operating checks will be accomplishedsimultaneously.In some instances it will be necessary to remove theinstrument panel bezel and the access panel on theinstrument panel to gain access to the valve. Block orhold vehicle by means other than the parking brake whileperforming the Service Checks.1.With both control knobs out, charge the air brakesystem to 448 kPa (65 psi), and check forleakage. No leakage permitted.2.With supply pressure still at 448 kPa (65 psi),push the red knob in. The knob must stay in.Leakage at the exhaust port must not exceed a25 mm (1") bubble in 5 seconds.3.Push the yellow knob in. With the engine offapply the foot valve several times to deplete theair supply. The red knob must pop outCTS-4079 - CHAPTER VII - Page8
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