Around 1966, I did my first brake job on my '56 Chevy. A friend helped me and all that was involved was a set of brake shoes (asbestos, of course) that I bought from a local parts store in Lexington, Kentucky. I had a Craftsman box of tools (metal box) for $39.95. There weren't any brake tools as such, but we survived with some needle nose pliers, vise grips and several screw drivers. We also had protective goggles (my friend had a visual disaster by not using his, when a retracting spring came loose!). We put the shoes on the hub, adjusted the axle nut until we locked down the wheel, then backed off until the wheel would spin freely about a turn and a half, put in the cotter pin and we were Saturday night ready. All this was done in the driveway with a small jack and two jack stands, with me sitting on a plastic tray on loan from our friendly drive in restaurant. Simple times!
Now, many years later, here's what I have learned: The principle of hydraulic brake operation is based on Pascal's Law, pressure applied to a confined body of fluid is transmitted equally and undiminished in all directions throughout the liquid. Thus, foot pressure to the brake pedal is transmitted to each wheel equally and all four brakes are applied with equal force. So that's what was happening in '66, I just didn't know it.
This will be the first of a several-part article on duo-servo self-energizing brakes on these three cars, all Bendix , a 1951 Chevy 2 door Fleetline. This was the first year for the Bendix  brakes for Chevy. In 1950, they were the old Huck style.
We will also cover a 1946 Super Custom 8 and a 1951 Packard Mayfair 250. On the Packards, only the fronts were done, as the rears were done and covered in previous DOC articles. First, a description of servoself-energizing type brakes which are hydraulically operated. Hydraulic brake operation is when the brake pedal is pushed and the shoes are forced against the drums. The turning of the drums rotates the shoes in the same direction. The wrapping action of the shoes uniformly increases the pressure at every point around the braking surface, which increases the stopping ability with less physical effort from the driver. The effect on the brake shoes is the Primary Shoe (short shoe to the front) follows the rotation of the drum for a short distance and pushes on the Secondary Shoe via the star adjuster at the bottom. With the forward rotation, the force on the Secondary Shoe is applied aheadof the pin connection, causing it to jam across the drum at a pressure much greater than that of the Primary Shoe. The action of the Secondary Shoe being far greater than the Primary Shoe makes it necessary for the Secondary Lining to be longer. This allows the Primary and Secondary linings to wear at the same rate. The duo-servo also applies to the backing of the car in stopping and backing. When backing, the Primary Shoe becomes the Secondary Shoe and the Secondary becomes the Primary, and the same duo-servo principle applies.
The essential units of the hydraulic brake system and their functions are:
1. The Master Cylinder supplies the hydraulic force.
2. The Brake Pedal applies this force to the master cylinder and multiplies the drivers effort.
3. The Brake Backing Plate supports the brake parts at each wheel and transmits the braking force to the frame of the car.
4. The Brake Shoes support the lining and transmits the braking force to the brake plate.
5. The Brake Lining and Brake Drum produce the friction and convert the power of the moving car into heat.
6. The Wheel Cylinders actuate and apply the pressure to the brake shoes.
7. The Steel Tubes and flexible hoses transmit the hydraulic pressure from the master cylinder to each wheel cylinder.
With these principles of the duo-servo brake system, I began work on my car. Jason and I started with the 1946 Packard Custom first. The '51 Chevy and the '51 Packard were on my two lifts and, you guessed it--fifty years after my first brake job, I was sitting on the driveway with a jack and two jack stands doing a brake job. Sometimes time can be so cruel.
The '46 rear wheels were chocked and the front end was raised and secured with two jack stands. Movers' blankets were laid down, tools laid out and an air hose run to my impact gun to remove the wheel lug nuts. The hub caps have cloisonne medallions, so they were put into the garage on clean microfiber towels. The problem with this car's brakes was that the steering wheel would pull hard to the left when the brake pedal was pushed. I had replaced a leaky master cylinder a month before and I knew the lines all bled out okay, so it must be in the linings or drums. These Senior Packards (41-50 356 CID) had 2 1/4" linings and they had a rather unique lock nut assembly on the front axle hubs. When the hub and bearings were on, an inner hex nut was put on with a pin that faced outward. There is a groove in the axle and a lock ring with a series of holes in it, and a teat that fits into the axle groove. The lock ring slides on the axle teat in the groove and one of the holes lines up with the pin on the inner nut. This sets the hub so that it is not too loose or too tight. Then the outer nut goes on and is tightened up against the lock ring and the cotter pin goes in. The Junior cars such as the '51 Packard Mayfair has the conventional one-nut arrangement.
Wearing our safety goggles, we removed the wheels' five lug bolts and laid the tires out separately. (If you lay a whitewall against another tire, it can leave a stain on the whitewall.) Then we took pictures of everything, removing the dust cap, outer bearings and, to get the inner seal out unhurt, we found a nut to fit the spindle, ground the edges round with a belt sander, and put it on the spindle. (Original hex nuts wont work because the round hub catches on it.) Then, we pulled the drum straight off and the round nut pulled the rear seal and bearing out the back of the hub, held on by the round nut. Next, we (1) removed the shoeshold springs and clips, (2) removed brake shoe return springs (be sure to mark primary [front] and secondary [rear]). The secondaries are stronger. Ours our color-coded yellow and the primaries are orange. (3) Spread the shoes and removed the star adjuster and connector spring. The above will come off with the shoe.
It was a great time to undercoat the wheel well, strip and paint the backing plate and replace the brake hoses and wheel cylinders.
We will continue with this next time.
Winter's a great time to complete the projects!
Keep 'em driving!