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Brake Bleeding
Purging air and moisture from your binders
Tom Morr / autoMedia.com
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Remember that brake systems are closed, so loss of fluid indicates a problem somewhere. When a master-cylinder reservoir is low, look for the cause instead of just topping it off with fluid. The system either has a leak somewhere or the brake pads are worn, causing the pistons to be more extended and retain more fluid.
DOT Specs
Most do-it-yourselfers are familiar with DOT 3 brake fluid, the grade most commonly recommended for passenger vehicles. The Department of Transportation (DOT) numbers refer to the fluids' minimum boiling points, rated both as "dry" (no moisture in the system) and "wet" (3% moisture). The wet rating is more meaningful for vehicles that don't receive regular fluid flushes.
The two brake-fluid styles: poly glycol ether (commonly known as "glycol") and silicone-based. Glycol-based brake fluid is available in DOT 3, 4, and 5 ratings. It's hydroscopic and compresses less than silicone fluid, which gives a firmer pedal feel. Glycol's main drawback is that it makes paint bubble if it comes in contact with it.
The DOT 5 grade is reserved for silicone-based fluid. Unlike standard glycol fluid, it doesn't eat paint (which is why DOT 5 is popular with the show/collector-car crowd) or absorb water. Theoretically, this makes it a "lifetime" fluid. However, if moisture gets into the silicone fluid, droplets can form and boil, which produces steam and introduces air into the system. Silicone fluid is also more expensive and more compressible than glycol, so it gives a mushier pedal feel. Never mix the two styles of fluid—the system must be completely flushed if changing from silicone to glycol or vice versa.
Two-Person Flushing
Now that we've hammered home the importance of bleeding and flushing brake fluid, here's how to do it properly. The traditional "two-man" method involves one person stepping on the brake pedal (whom we like to call The Pumper) while the other (The Dumper) opens the bleeder screws at the brakes. Verbal communication is critical so that the pedal is never up while the bleeder is open, which draws air into the system.
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Brake bleeding is cheap and relatively easy. All that's necessary are brake fluid, plastic tubing, a wrench (ideally a flare-nut/"line" wrench or 6-point socket to initially open the bleeder) and a clear bottle.
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The wheel-bleeding sequence varies depending on vehicle (front- or rear-wheel-drive) and method (1- or 2-person). For most rear-drive vehicles, begin at the wheel farthest away from the master cylinder (usually the passenger's side rear).
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Attach one end of the tube to the bleeder screw and put the other in a clear bottle to view air bubbles. Crack open the bleeder with a wrench while an assistant applies pressure to the brake pedal.
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Keep pumping and bleeding until air bubbles no longer gurgle in the tube and bottle. Then go the extra step and flush the system, continuing to bleed until only fresh brake fluid comes out.
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Top off the master cylinder periodically to make sure that the reservoir doesn't run dry and reintroduce air into the system. Keep the lids on both the master and bottle during bleeding to keep air out and fluid in.
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Old, contaminated glycol brake fluid is muddy brown. Dispose of it properly at an approved collection site. Recently introduced tinted brake fluids that makes a complete flush more obvious.
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Re: Chevy 3.8L Engine cutout I would call it in intermediate job. You will need some special tools to do it, but if you have some experience doing repairs, and not jus ... more... |
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