Leakage of Gear Oil onto Brakes

The most common reason for leakage of oil from differential gear cases onto brakes is overfilling of the housing. Under such conditions, the leakage will probably take place no matter how effective packing may be. Use of quite low viscosity gear lubricants, for example, SAE 75 grade in hot weather may also contribute to such leakage. Use of air pressure to help remove oil from the gear box may also cause leakage onto brakes. Failure of packing should also be investigated case there is a problem of gear lubricant on brakes.

Venting Gear Housings

While Forbes et al.^20  mention that gear housings should be vented so that oil vapors may escape, such openings  may  tend to permit  entrance of humid air. In fact water has been drawn off from gear cases which could only have arisen from condensation. If such conditions generally prevail, the gear oil should contain a rust preventive additive. Cartridges or filters containing dehydrating agents and attached to the vent of gear cases are not too practical because of the necessity of frequent renewal. Removal of condensed water from circulating systems is simpler than where the gears are bath lubricated. Entrance of contaminants other than water through gear housing vents is possible and often problem. The location and atmosphere surrounding the gear set will determine such possibilities and also what corrective measures need be taken. Thus, gear cases of large tractors, such as are used on road and construction work, have a breather with an air filter which should be renewed at 250 hours operation intervals. One manufacturer reports some trouble with dirt in gear cases probably due to the filter not being changed at the required interval. Farm tractors also have the same problem and a proper air filter and frequent renewal is desirable on vents from gear cases. 

Automobile and truck gear cases are subjected to similar contamination. Thus, a large car manufacturer  mentioned in a service bulletin that two major  contributing factors  to  a considerable number of ring and pinion  failures in axles  was moisture  and  foreign  materials  entering  the axle  and contaminating the lubricant. The corrective action was to install a new vent system. The vent was fitted with a hose and hose clamp. The hose, 19 inches  long , goes  up under  the  frame  and  body of the car  and  is  clamped  so  that  the  open  end  faces  toward  the  side of the  vehicle.

Industrial gear set installations may require similar filters or extensions of gear case vent opening to points where the concentration of contaminants is at a minimum.