My 2001 E150 van has rear drum brakes. If you look under the van, at the inside of the drum housing, there is a grease fitting above the axle. My question is what exactly is that grease fitting serving?

 

Hi Polly !
That fitting that looks like a grease fitting is the hydraulic brake rear wheel cylinder bleeder fitting.
It is used to remove air from the brake hydraulic system at that wheel location. If the rear brake hydraulic system is opened for any reason and fluid leaks out most of the time air takes its place and needs to be removed by "bleeding" the air out. Fluid cannot be compressed so when the brake pedal is depressed that pressure is transmitted to the system. When air gets into the system , air can be compressed, and the result is a spongy pedal and braking is reduced. Hope I answered your question!

 

Thanks Hanky.... mystery solved!