My rear disc brakes with the emergency drum brake

disc brakes with emergency brake
An example of a drum emergency brake with regular disc brakes. 

This was the good news! Something strange happened to me last week. I loaded the garbage and the recycling into the minivan to do the Saturday trip to the transfer station, and the right rear wheel locked up when I backed up. As this happened, the rear axle made unpleasant noises. I thought the parking brake was seized, and was relieved when the wheel moved ok going forward. 

On the way home, the right rear wheel locked up while driving forward, making horrific noises. Again, I thought the noise was originating from the rear axle. I definitely heard the differential banging against the frame cross member it is mounted on. I drove up my driveway, with the wheel seized. I googled the problem, and found many stories of the rear differential failing, causing a rear wheel to lock up. Fortunately, the part is available rebuilt, but they are expensive. 

I planned on removing the differential to verify it was in fact bad before I purchased a used or rebuilt unit. I thought I should check the right rear hub first to rule out any problem there. Fortunately, I found the problem. This vehicle has four wheel disc brakes, with the parking brake on the rear. The parking brake has conventional brake shoes on a drum in the center of a “hat” type rotor. Somehow, something came apart with the parking brake assembly, and the whole assembly broke apart and jammed against the rotor. I have to replace the backing plate, caliper mount, rotor and the whole parking brake assembly. It is bad, but infinitely better than a bad differential. I have never seen anything like this before. 


A few more points about BEARINGS 

Pictured below, and the following is an article from the December, 1960, “Science and Mechanics” magazine. 

Bearing Lubricates Itself 

wheel bearings

Designed to replace ball bearings and have several times their life expectancy, this new Hy-Film bearing never requires relubrication. It utilizes the phenomenon of hydrodynamic oil film. The diagram at left: (1) Oil is drawn from reservoir through bearing window; (2) rota-tion of inner tace under load generates hydrodynamic oil film, supporting race without metal contact; (3) oil forced to bearing ends by film pressure lubricates thrust washer and (4) oil is picked up by slinger and returned to retaining cup, where it is reabsorbed by Permawick in oil return hole. Tann Bearing Company of Detroit, Michigan, designed and developed the bearing. 

What is hydrostatic and hydrodynamic bearing? Hydrostatic bearings are externally pressurized fluid bearings, where the fluid is usually oil, water or air, and the pressurization is done by a pump. Hydrodynamic bearings rely on the high speed of the journal (the part of the shaft resting on the fluid) to pressurize the fluid in a wedge between the faces. 

What are the types of bearings? There are many types of bearings, each used for different purposes. These include ball bearings, roller bearings, ball thrust bearings, roller thrust bearings and tapered roller thrust bearings. 


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I am running out of ideas on what to write about in this column. If you have any ideas, or any questions you want me to answer, please let me know. 

Dave’s Garage…email: dasander@aol.com 

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