HYDRAULIC SCRAPERS Braking System Caterpillar

Braking System

The scraper has air pressure controlled brakes on the rear wheels. These brakes are operated by the same foot operated air brake control valve that operates the tractor drive wheel brakes. See the Operation and Maintenance Instructions for the tractor.

Make sure that the brake hose connection between the tractor and scraper is tight to prevent air leaks.

Two air lines are routed to the rear of the scraper through the bowl side. One line always carries system pressure and connects to the air supply tank thereby supplying it with system pressure. The second line connects the foot valve on the tractor with the control and quick release valve (1) which is used to route air from the supply tank to the rotochambers (2). Air pressure from the foot valve actuates the valve (1). The purpose of the supply tank is to obtain quicker actuation of the rotochambers since the line from the supply tank is much shorter than one required to bring pressure air to the rotochamber from the foot valve.

Rotochambers convert compressed air energy into mechanical force to apply the brakes. Air entering the brake rotochamber forces the push rod (3) out thus rotating the slack adjuster (4), brake camshaft (5) and brake cam, applying the brakes. The higher the air pressure in the rotochamber, the greater the pushing force of the brake linings against the drum. When all the air pressure is released from the chamber, the brake shoe release springs and the rotochamber release springs, release the brakes.

1-Control and quick release valve. 2-Rotochambers. 3-Push rod. 4-Slack adjuster. 5-Brake camshaft.

1-Free travel at this point should be 2 inches (3.18 cm.) for 630 and 631; 2.50 inches (4.45 cm.) for 657, 651, 650, 641 and 632; and 2.75 inches (5.08 cm.) for 666 and 660. 2-Locking bolt. 3-Adjusting worm.

Adjustment: Every 250 service hours check the free movement of the slack adjuster arm. As the brake linings wear the free movement of the slack adjuster increases between the applied and released positions. When the free movement reaches three inches an adjustment should be made.

Adjustment is accomplished by turning the locking bolt (2) (counterclockwise) one half turn then turn the adjusting worm (3) in or out to decrease or increase the slack adjuster arm travel between engaged and disengaged positions. After proper adjustment has been obtained turn locking bolt (2) one half turn (clockwise) to lock the adjusting worm (3).

Testing Rotochambers: See that the push rods (1) move in and out without binding. Check the push rod travel for correct adjustment and the dust boot for cracks. With brakes fully applied, check for leakage through the diaphragm by removing the rubber boot (2) and coating the clearance hole around the push rod with soap suds. If any leakage is found, the diaphragm must be replaced.

1-Push rod. 2-Rubber boot.

Testing Quick Release Valve: Apply the brakes and cover the exhaust port of the quick release valve with soap suds. If dirt is on the exhaust valve seat or if the seat is worn leakage will be noticed. Disassemble the valve and remove the dirt or if the seat is worn install a new diaphragm assembly.

Draining the Air Tank: The scraper air tank is located on the back of the bowl beneath the top sheet of the push frame. There is a drain valve in the bottom of the tank which permits draining of the moisture which condenses in the tank. This valve should be opened daily by turning the valve handle 1/4 turn.