Mechanical brakes were used on most cars until being replaced by hydraulics in the mid-to-late-1930's. Our '36 Packard 8 Rumble Seat Coupe has them. Packard introduced hydraulic brakes in their junior line with its new 120 Series in 1935, but retained the mechanical system in its senior cars (8's, Super 8's and V-12's) until 1937.
One definition of mechanical brakes is that they incorporate cables that link the brake pedal with the brake shoe operating mechanism, and is activated by depressing the brake pedal, which pulls against the cables, expanding the shoes against the brake drums. The mechanical system worked pretty well on most cars, especially with a vacuum power booster, as on our '36. When compared with our '37 Packard Super 8s hydraulic brakes, there is very little performance difference. They both stop quickly with very little pedal pressure.
Upon the purchase of our '36, there was a continuous engine flutter, and the engine stalled when we applied the brakes. This turned out to be a bad gasket in the vacuum power assist unit, creating an engine vacuum leak. It was easy to repair, by removing the unit and replacing the paper gasket in it. While the booster was being repaired, it was also a good time to go through the entire braking system.
These procedures are for Buick 40, Hudson, Lafayette, Lincoln, '35-'36 Packard 8's, Super 8's & 12's, Terraplane and Willis - 1935. All are Bendix* (duo-servo, single anchor type). There are two types of single anchor: One type is sliding anchor and the other is eccentric anchor. We will cover eccentric anchor in this article. To start, we put the car on the lift and removed the wheels and brake drums. We cleaned and lubricated linkages and clevises so that the brake cables would work properly and return to their original position when the brake pedal or hand brake was released. We also checked all the return springs and made sure the brake linings were of the correct thickness, not cracked and were free from oil and grease. With all this serviced, we put the drums back on to adjust the brakes. There are only two adjustments for brake lining wear:
1. The Notched Star adjusting screw that centralizes clearance between the linings and the drum, and
2. The Eccentric adjustment which centers the brake shoes in the brake drum.
No adjustment should be made in the brake control system (cables, linkages, etc., to compensate for lining wear unless you replace the brake shoes.)
For the notched star adjustment (similar to regular hydraulic brake adjustment), with all four wheels in the air, brake drums on and cables disconnected: Expand the brake shoes by turning the notched star adjustment screw until the brake drum can just be turned by hand. Pull the cables by hand toward the cross shaft or rotary control to remove all the cable slack and lost motion at cam levers. Make sure the clevis pin will just enter the clevis and lever freely. Lock the clevis jam nuts and insert the clevis cotter pins and make the following adjustments:
At each wheel, insert a .010" feeler gauge at the top of each drum between the lining and the brake drum. It should also be .010" when checked through inspection slots in the brake drum, on each end of the top brake shoe (near star adjuster and anchor pin). If adjustment for worn linings is necessary, adjust by turning the star wheel adjusting screw until a light drag is felt while turning the brake drum, then turn the adjustment screw in the opposite direction until the drum is just free from drag. Depress the brake pedal until the wheel with the least brake drag can just be turned by hand, then back off the adjusting screw on the tight brakes until the drag is alike on all four wheels. The brake pedal should not go down more than halfway when depressed. If the pedal goes more than halfway, readjust the brakes, then road test. There shouldnt be any pull or locking up when the brakes are applied.
For eccentric adjustment with all four wheels in the air and drums on, disconnect the cables leading to the front and rear brakes at the cross shaft levers or rotary control by removing the clevis pins. Remove star adjustment hole covers from the brake backing plates and the inspection hole covers from the brake drums. Lubricate the brake pedal, hand brake lever, cross shaft or rotary control bearings, overrunning linkage and all clevises. Make sure that all of the above operate freely and that the linkages return quickly upon release. Loosen the eccentric* lock nut and insert a .010" feeler gauge between the lining of the top shoe and the brake drum (for Packard). See your manual for your particular setting. Loosen the anchor pin one turn and tap the anchor pin with a soft hammer up or down to get proper shoe clearance. Turn the eccentric in the direction of forward wheel rotation until the feeler gauge is just snugwhen inserted into the adjustment holes near the star adjuster and the anchor pin (in other words, at each end of the top shoe.) Tighten the eccentric lock nut, holding the eccentric carefully in its position. The clearance at both ends of the top shoe should not vary more than .003" If it does, it will be necessary to move the anchor pin. If its not possible to get within .003" variance, then get as close as you can and make clearance at the anchor end of the shoe less than at the star adjuster end of the top shoe. Do not adjust the anchor pin unless its absolutely necessary.
When the correct settings are made on all four brakes, put everything back together and road teat. We let our shoes wear in for a few days and then recheck all brake adjustments.
We completed this service on our '36 over 12 years ago, and the system still works beautifully. It may be very old school, but when mechanical brakes are working correctly, and youre using old-style soft linings and a power booster, it is an excellent system. I know ours works great, and I wouldn't change a thing! See you next month and keep 'em driving!
*Servo Action: When brakes are applied while the wheels are rolling, and the brakes leading shoe tries to rotate in the direction of the drum, then forms a wedge against the drum, stopping the rotation.
*Duo-Servo: When servo action works in both forward and reverse rotation.
*Eccentric: Deviating from a circular path.