Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 333 (DISC BRAKES)BLEEDING BRAKE SYSTEMHYDRAULIC BRAKE SYSTEM FLUSHING
1999 GMC Forward Control 5.7 R, Automatic
Hydraulic Brake System Flushing
1999 GMC Forward Control 5.7 R, AutomaticSECTION Hydraulic Brake System Flushing
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
When adding fluid to the brake master cylinder reservoir, use only Delco Supreme 11, GM P/N 12377967, or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container. The use of any type of fluid other than the recommended type of brake fluid, may cause contamination which could result in damage to the internal rubber seals and/or rubber linings of hydraulic brake system components.
- Inspect the brake fluid for the following conditions, indicating brake fluid contamination:
- Fluid separation, indicating 2 types of fluid are present; a substance other than the recommended brake fluid has been introduced into the brake hydraulic system:
- Swirled appearance - oil-based substance.
- Layered appearance - silicone-based substance.
- Fluid discoloration, indicating the presence of moisture or particles that have been introduced into the brake hydraulic system:
- Cloudy appearance - moisture.
- Dark appearance - suspended particles in fluid; dirt, rust, corrosion, brake dust.
- Fluid separation, indicating 2 types of fluid are present; a substance other than the recommended brake fluid has been introduced into the brake hydraulic system:
- Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for swelling, indicating brake fluid contamination.
- If the brake fluid WAS contaminated with an oil-based or a silicone-based substance, indicated by fluid separation and/or a swollen master cylinder reservoir cap diaphragm and/or swollen reservoir-to-master cylinder grommets, perform the following:
- Remove all of the following components listed from the vehicle. Each component contains internal rubber seals/linings which have been contaminated by the contaminated brake fluid in the brake hydraulic system. See the procedures indicated:
- MASTER CYLINDER under REMOVAL & INSTALLATION.
- FRONT BRAKE HOSE under REMOVAL & INSTALLATION.
- REAR BRAKE HOSE under REMOVAL & INSTALLATION.
- FRONT BRAKE CALIPER under REMOVAL & INSTALLATION.
- REAR BRAKE CALIPER under REMOVAL & INSTALLATION.
- BRAKE PRESSURE MODULATOR VALVE (BPMV) under REMOVAL & INSTALLATION in appropriate ANTI-LOCK article.
- Clean out all the hydraulic brake pipes using denatured alcohol, or equivalent.
- Dry the brake pipes using non-lubricated, filtered air.
- Repair or replace all of the following components listed and install them to the vehicle. Each component contains internal rubber seals/linings which have been contaminated by the contaminated brake fluid in the brake hydraulic system. See the procedures indicated:
- MASTER CYLINDER under OVERHAUL or MASTER CYLINDER under REMOVAL & INSTALLATION. Also perform the following: Clean the brake master cylinder reservoir using denatured alcohol, or equivalent, then dry the reservoir using non-lubricated, filtered air. Inspect the reservoir for cracks and/or damage and replace if necessary. See MASTER CYLINDER RESERVOIR under REMOVAL & INSTALLATION. Replace the brake master cylinder reservoir cap diaphragm.
- FRONT BRAKE HOSE under REMOVAL & INSTALLATION.
- REAR BRAKE HOSE under REMOVAL & INSTALLATION.
- FRONT BRAKE CALIPER under OVERHAUL or FRONT BRAKE CALIPER under REMOVAL & INSTALLATION.
- REAR BRAKE CALIPERS under OVERHAUL or REAR BRAKE CALIPER under REMOVAL & INSTALLATION.
- BRAKE PRESSURE MODULATOR VALVE (BPMV) under REMOVAL & INSTALLATION in appropriate ANTI-LOCK article.
- Remove all of the following components listed from the vehicle. Each component contains internal rubber seals/linings which have been contaminated by the contaminated brake fluid in the brake hydraulic system. See the procedures indicated:
- If the brake fluid was NOT contaminated with an oil-based or a silicone-based substance, but WAS contaminated with water or dirt, rust, corrosion, and/or brake dust, replace the brake master cylinder reservoir cap diaphragm. The diaphragm may have allowed the moisture or particles to enter the hydraulic system.
- Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11, GM P/N 12377967 (Canada P/N 992667) or equivalent, DOT-3 brake fluid from a clean, sealed brake fluid container.
- Pressure bleed the hydraulic brake system. Begin the procedure with the pressure bleeder reservoir filled to the maximum-fill level with the correct brake fluid as indicated. See PRESSURE BLEEDING .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.