YOKE 4F3084 - Caterpillar

Bleeding The Accumulator Lines
If the lines between the accumulators and the service brake valve have been disturbed, air can be purged from this side of the system using the bleed valves on the accumulators.1. Attach a length of clear plastic tube to the accumulator bleed valve which is furthest away from the service brake valve. Fix the free end in a suitable container.2. With the engine stopped, slowly open the bleed valve and allow oil to flow until it is free of air.3. When oil flows free of air, close the bleed valve. If oil does not flow free of air, close the bleed valve, run the engine for one minute to re-charge the system and repeat the procedure. The engine MUST be stopped when the bleed valve is opened.Bleeding the Parking Brake
The parking brake is self bleeding. No bleed valve is provided for release of air in the lines.After service work involving disassembly of the parking brake or any system components, block the wheels and engage/disengage the brake ten times to ensure air is purged from the lines. The disconnect switch must be ON before the parking brake can be disengaged.Accumulator Precharge
Dry nitrogen is the only gas approved for use in the brake accumulator. The charging of oxygen gas in these components by accident will cause an explosion. This danger can be avoided by the use of nitrogen cylinders with standard CGA (Compressed Gas Association Inc.) No. 580 connections. When nitrogen gas is ordered, be sure to order cylinders with CGA 580 connections. Do not rely on color codes or other methods of identification to tell the difference between nitrogen and oxygen cylinders. In any application never use an adaptor to connect your nitrogen charging group to a valve outlet used on nitrogen as well as oxygen or other gas cylinders. Be sure you use dry nitrogen.
Checking Service Brake Accumulator Precharge Pressure On The Machine
Accumulator precharge can be checked on the machine using the following procedure. However, this check is only an indication that at least one accumulator is precharged. It does not indicate that one or more accumulators have failed.The parts listed in the topic "Service Brake Cut In and Cut Out Pressures" are needed to check precharge in the rear brake accumulators.1. Carry out steps 1 to 4 of the procedure described in the topic "Service Brake Cut In and Cut Out Pressures" to check both front and rear brake accumulator precharge.2. With the engine stopped, have an assistant make repeated light applications of the service brake pedal and observe the pressure gauges. As successive brake applications are made the pressure gauge readings will fall. When the pressure reaches accumulator precharge, it will suddenly fall to zero. This should occur at a pressure of 8500 kPa (1230 psi).All accumulators are pre-charged to the same pressure.3. When testing is complete, remove the test equipment.4. Start the engine and allow to operate at low idle to re-charge the brake system.Tracing A Failed Accumulator
If it is suspected that