There are other bleeding methods. Vacuum bleeding has gained popularity, and for good reason. Vacuum applied at each wheel cylinder's bleeder valve will draw old fluid, air and contaminants from the confines of the cylinder. Instead of pressurizing the master cylinder, vacuum bleeding pulls air bubbles and contaminated fluid from within each wheel cylinder. By adding enough clean brake fluid at the master cylinder, vacuum bleeding can flush the entire system.

Brake fluid for drum brakes is DOT 3 rated. Use high-temperature-rated DOT 4 for drum/disc systems. You can also use DOT 4 in a four-wheel drum brake system. DOT 3 and DOT 4 brake fluids are compatible.

Silicone DOT 5 brake fluid does not draw moisture. Some use this fluid in a vehicles parked for long periods. When changing to DOT 5 silicone fluid, you must completely flush and dry the brake hydraulic system. New rubber must be installed at the master and wheel cylinders. DOT 5 is not compatible with DOT 3 or 4. Never mix DOT 3 or DOT 4 with DOT 5.

When performing brake work, use a factory workshop manual to determine the layout of parts, the sequence of fit-up, and acceptable tolerances. Keep parts separated per wheel to ensure correct reassembly. An older truck will have a history of brake work, and parts could be out of position or even missing. Compare what you have to factory guidelines and parts illustrations. Use factory service methods for the safest results.

Note: By the '70s, factory service manuals no longer recommend cylinder honing. Light stain removal remains acceptable, using crocus cloth only, followed by careful cleaning and renewal of all rubber parts. Signs of corrosion, pitting, or score lines call for a new cylinder.

What Did You Learn This Month?
Night School would not be complete without a quiz! Don't worry about your test-taking skills or grades. This is an open-magazine, true or false test. Clues can be found within the Night School text, photos and captions. Have a good month!

True or False Questions:
1. Bendix duo-servo brakes date back to 1939 and are still in use today. Earlier applications require manual adjustment. In the '60s, self-adjusters became popular.

2. On Bendix duo-servo brakes, the front (primary) brake shoe has shorter lining than the rear shoe. Reversing the shoes will decrease braking efficiency.

3. If a 50-year-old wheel cylinder leaks from worn-out rubber and corrosion, it is OK to replace the leaky cylinder and leave the other old wheel cylinders alone. After all, they're not leaking now.

4. The vacuum brake bleeding method pulls old fluid out through the bleeder valve. Vacuum is very effective at removing contaminants.

5. Breathing asbestos dust is very harmful. Older brake shoes with asbestos lining must be handled safely. Asbestos-free replacement lining is better for your health.

6. Before 1962, Chevrolet and GMC light trucks used ball-type front wheel bearings. Adjustment specifications for ball and roller bearings are not the same.

7. It is perfectly OK to mix wheel bearing grease types. If you're in a hurry, just pack fresh grease over the top of old grease.

8. Mineral oil and solvents are highly damaging to rubber brake parts. Gasoline, petroleum distillates, solvents, kerosene, lacquer thinner, and motor or gear oil should never be used around rubber brake parts. Wash hands with soap and water before handling rubber parts.

9. Use isopropyl or denatured alcohol for cleaning hydraulic brake cylinders. Use rubber gloves to keep toxic alcohol from entering your bloodstream through nicks and cuts.

10. A dual master cylinder with a bellows seal cap is far safer than a vintage single master cylinder mounted beneath the floorboard. Single master cylinders vent to atmosphere and draw moisture and contaminants into the braking system.

true true false true true true false true true true

LMC Truck
Inline Tube
33783 Groesbeck
MI  48026
National Parts Depot
900 SW 38th Ave
Fl  34474
Master Power Brakes
254-1 Rolling Hills Rd.
NC  28117
Sacramento Vintage Ford