03 Brake System
Brake System
• Front brakes are air applied disc
• Rear brakes (Figure 3-1) double as parking brake
- Park brakes are spring applied – air released
- Two large drum brakes
- Park brake remains applied even if air pressure is lost
• If air pressure is lost
- A buzzer and warning lamp will alert you
• Chassis is equipped with automatic slack adjusters (Figure 3-2)
- No brake adjustment required
The rear brakes on the PowerGlide chassis are also used as the parking brakes. This provides you the holding power of two large drum brakes to prevent your coach from rolling, even when fully loaded on a 20% grade.
A decrease in air pressure while driving will not cause an immediate loss of brakes. If a significant leak develops in the air system, at approximately 60 PSI you will be alerted by a lamp on the instrument panel, and by an audible alarm. As you apply the brakes, the air supply holding the park brakes in the released position will gradually be depleted. When system pressure drops to approximately 40 PSI the rear brakes will set. This allows you sufficient time to pull over to the side of the road.
NOTE: The rear brakes have dual chambers – one for the service brakes and one for the park brake. The service brakes are air applied and spring released. The park brake is spring applied and air released.
The brake system is equipped with automatic slack adjusters that avoid the need to manually adjust your brakes. Each time you step on the brake pedal, if adjustment is needed, the adjusters will take up the slack.
Compressed Air System
The compressed air system is comprised of multi-air storage tanks. The primary tank stores and supplies air for the rear brakes, the secondary tank stores and supplies air for the front brakes.
When air is compressed it becomes hot. As it cools, condensed moisture forms in the system. The air system is equipped with an air dryer to remove most of this moisture. The dryer has an automatic moisture ejector that releases the trapped moisture back into the atmosphere. However, some moisture will form in the system beyond the dryer, and make its way into the storage tanks. As moisture collects in the primary and secondary tanks, it displaces the area needed for air storage, thus requiring that the tanks be drained periodically.
The air system is equipped with air tank drains conveniently located in the compartment with the DEF tank. Each drain is attached to a different tank. These drains should be opened regularly for a few seconds to remove any moisture trapped in the tanks.
Air Dryer
The Tiffin PowerGlide chassis air brake system features a Haldex Purest air dryer (Figure 3-3), which removes the condensed moisture from compressed air. The air dryer is equipped with a desiccant cartridge that needs to be changed every 36 months. The dryer is located on the driver's side (LH) frame rail (behind the rear axle).
Engine Brake
Exhaust Brakes cannot be used on ISB engines with common rail fuel systems. The variable geometry turbocharger (VGT) takes the place of the exhaust brake and requires no maintenance. The VGT works in conjunction with the engine and transmission to provide an integrated braking system used to help slow the vehicle. This braking power is achieved by modulating the turbo sliding nozzle ring to restrict the flow of exhaust gases from the engine, which in turn creates a high back pressure on the engine. The high back pressure creates a high level of resistance to the motion of the pistons within the engine and this resistance is used to reduce engine speed and thus vehicle speed. The engine brake feature will only function when the driver turns the exhaust brake switch to the on position. Once the switch is in the on position and the vehicle is moving faster than 8 k/h (5 MPH); the exhaust brake will operate when the driver removes pressure from the throttle pedal allowing the engine to see 0% throttle and 0% fuel delivery and taps the service brake. Engine braking is most effective when the engine RPM is higher. The automatic transmission has been programmed to downshift more aggressively when the exhaust brake is enabled to increase brake performance.
As mentioned above:
The engine brake is activated when the following conditions are satisfied:
1. The engine brake switch is in the “ON” position
2. The accelerator pedal is released
3. The vehicle is moving faster than 8 k/h (5 mph)
4. The service brake is depressed momentarily