Leaking Axle Seals
Axle seals are rubber radial shaft seals that keep lubrication in while keeping water and debris out. They can fail and leak from wear or damage.
They harden over time, allowing differential fluid to bypass the seal and soak into and contaminate the brake shoe's lining. It can be seen on the backing plate or even splashed across the tire.
A semi-floating solid axle has a sealed bearing and an inner and outer seal. The outer seal is primarily to keep road debris and water out, and the inner seal prevents fluid from leaking from the differential. Most vehicles with solid rear axles have semi-floating axles installed. The axle shaft supports some of the vehicle's weight. Heavy-duty trucks that haul a lot of weight have full-floating axles. The axle floats; there is no weight placed on the shaft.
This axle has one seal at the end. The differential fluid flows to lubricate the bearing when the vehicle makes a turn. It's supported on the inside by the side gears and the outside by the axle bearing. The seal keeps the differential fluid in while keeping environmental contamination out.