Hydraulic Brake System Flushing

Hydraulic Brake System Flushing
Warning: Refer to Brake Fluid Irritant Warning (Brake Fluid Irritant Warning).


Caution: Refer to Brake Fluid Effects on Paint and Electrical Components Caution (Brake Fluid Effects on Paint and Electrical Components Caution).

1. 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

2. Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for swelling, indicating brake fluid contamination.
3. 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:

1. 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.
Refer to the procedures indicated:

* Master Cylinder Replacement (Automatic Transmission) (Master Cylinder Replacement (Automatic Transmission))Master Cylinder Replacement (Manual Transmission) (Master Cylinder Replacement (Manual Transmission))
* Front Brake Hose Replacement (With RPO LNF) (Front Brake Hose Replacement)Front Brake Hose Replacement (Without RPO LNF) (Front Brake Hose Replacement)
* Rear Brake Hose Replacement (Body to Axle) (Rear Brake Hose Replacement (Body to Axle))Rear Brake Hose Replacement (Axle to Caliper) (Rear Brake Hose Replacement (Axle to Caliper))
* Front Brake Caliper Replacement (With RPO LNF) (Front Brake Caliper Replacement)Front Brake Caliper Replacement (Without RPO LNF) (Front Brake Caliper Replacement)
* Rear Brake Caliper Replacement (Rear Brake Caliper Replacement), if equipped
* Wheel Cylinder Replacement (Service and Repair), if equipped
* Brake Proportion Valve Replacement (Service and Repair), if equipped
* Brake Pressure Modulator Valve Replacement (With JL4) (Service and Repair)Brake Pressure Modulator Valve Replacement (With JL4, LNF) (Service and Repair)Brake Pressure Modulator Valve Replacement (Without JL4) (Service and Repair), if equipped

2. Clean out all the hydraulic brake pipes using denatured alcohol, or equivalent.
3. Dry the brake pipes using non-lubricated, filtered air.
4. 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.
Refer to the procedures indicated:

* Master Cylinder Replacement (Automatic Transmission) (Master Cylinder Replacement (Automatic Transmission))Master Cylinder Replacement (Manual Transmission) (Master Cylinder Replacement (Manual Transmission)); 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. Refer to Master Cylinder Reservoir Replacement (Master Cylinder Reservoir Replacement).
Replace the brake master cylinder reservoir cap diaphragm.
* Front Brake Hose Replacement (With RPO LNF) (Front Brake Hose Replacement)Front Brake Hose Replacement (Without RPO LNF) (Front Brake Hose Replacement)
* Rear Brake Hose Replacement (Body to Axle) (Rear Brake Hose Replacement (Body to Axle))Rear Brake Hose Replacement (Axle to Caliper) (Rear Brake Hose Replacement (Axle to Caliper))
* Front Brake Caliper Overhaul (Without RPO LNF) (Front Brake Caliper Overhaul)Front Brake Caliper Overhaul (With RPO LNF) (Front Brake Caliper Overhaul)or Front Brake Caliper Replacement (With RPO LNF) (Front Brake Caliper Replacement)Front Brake Caliper Replacement (Without RPO LNF) (Front Brake Caliper Replacement)
* Rear Brake Caliper Overhaul (Rear Brake Caliper Overhaul)or Rear Brake Caliper Replacement (Rear Brake Caliper Replacement) , if equipped
* Wheel Cylinder Replacement (Service and Repair), if equipped
* Brake Proportion Valve Replacement (Service and Repair), if equipped
* Brake Pressure Modulator Valve Replacement (With JL4) (Service and Repair)Brake Pressure Modulator Valve Replacement (With JL4, LNF) (Service and Repair)Brake Pressure Modulator Valve Replacement (Without JL4) (Service and Repair), if equipped

4. 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 which may have allowed the moisture or particles to enter the hydraulic system.
5. Fill the brake master cylinder reservoir to the maximum-fill level with GM approved or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.
6. 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. Refer to Hydraulic Brake System Bleeding (Manual) (Service and Repair)Hydraulic Brake System Bleeding (Pressure) (Service and Repair)Hydraulic Brake System Bleeding (Rear Brake Caliper - Cobalt SS) (Service and Repair).