992K Wheel Loader and 854K Wheel Dozer Braking System Caterpillar

Caterpillar recommends checking the thickness of the service brake discs and the oil groove depth on both sides of each brake disc. Disc wear on each end of the machine and on each side of the machine may vary.

Replace the service brake discs as soon as possible when the depth of the oil grooves has reached the maximum wear limit. As the oil groove depth is reduced, the flow of the cooling oil is reduced. This causes heat to build up and the friction material wears rapidly.

Eventually, the friction material will completely wear away. This action causes the metal of the brake disc to contact the metal reaction plate. When friction material and metal particles are in the oil, the highly polished surface of the reaction plate will be destroyed. These brake components must be replaced.

If the metal of the brake disc is contacting the metal reaction plate, clean the entire axle thoroughly. If the axle is not cleaned correctly, the debris will continue to contaminate the oil. This contamination will cause premature failure of the service brakes.

Brake service life can vary greatly because of the extreme conditions in some applications. If the actual brake service life is less than the expected service life, there are several factors that could be causing premature wear:

• Water and debris can enter the axle through the lip seal at the drive yoke. If this action occurs, the water and debris can mix with the oil. This action could damage the seals in the axle.

• The breather could be plugged. This restriction could prevent the breather from venting correctly. Check the breather for damage and for debris.

• Excessive heat may be generated if the service brakes are used as a retarder to maintain a ground speed that is slower than normal. This type of operation should be avoided by using a lower transmission gear.

• Oil leaks can allow oil contamination to occur. Check for oil leaks at the yoke and along the drive axle.

If premature wear is suspected, obtain an S·O·S oil analysis prior to service repairs. This action will help to establish a possible cause or a remedy to the problem.

Illustration 1	g06221939
Service brake (A) Thickness of a brake disc (1) Piston (2) Brake disc (3) Reaction plate

The minimum thickness of a worn brake disc is 4.88 mm (0.192 inch). The thickness of a new brake disc is 6.10 ± 0.13 mm (0.240 ± 0.005 inch). Service the brakes before the thickness of the brake disc is less than 4.88 mm (0.192 inch).

Illustration 2	g00110142
Measuring the oil groove depth

Oil groove depth is the most critical dimension. If the oil grooves on the brake discs are too shallow or gone, oil flow will be inadequate. This occurrence will cause excessive wear and abrasion. See Table 1.

Use a depth gauge to measure the depth of the oil grooves on both sides of each brake disc in each axle housing. The depth of the oil grooves must be greater than 0.38 mm (0.015 inch).

Table 1

Brake Disc Wear Information
Percentage of Remaining Brake Disc Life	Disc Thickness	Oil Groove Depth
100	6.10 mm (0.240 inch)	1.05 mm (0.041 inch)
80	5.86 mm (0.231 inch)	0.92 mm (0.036 inch)
60	5.61 mm (0.221 inch)	0.78 mm (0.031 inch)
40	5.37 mm (0.211 inch)	0.65 mm (0.026 inch)
20	5.12 mm (0.202 inch)	0.51 mm (0.020 inch)
0	4.88 mm (0.192 inch)	0.38 mm (0.015 inch)