Service Manual2007 Aveo MASTER CYLINDER

SECTION 4B

MASTER CYLINDER

SPECIFICATIONS

Fastener Tightening Specifications

Application	N•m	Lb-Ft	Lb-In
Brake Lines	16	12	-
Master Cylinder Attaching Nuts	18	13	-
Proportioning Valves	40	30	-
Bleeder Valves	6	-	53

MAINTENANCE AND REPAIR

ON-VEHICLE SERVICE

Master Cylinder Assembly

Removal Procedure

Disconnect the electrical connector from the reservoir.

For vehicles with the ABS braking system, disconnect the brake lines from the master cylinder body.
For vehicles with the non-ABS braking system, disconnect the brake lines from the proportioning valves.
For vehicles with the manual transaxle, disconnect the clip to the clutch hose connection at the master cylinder.
Plug the opening to the brake lines to prevent fluid loss and contamination.

Remove the attaching nuts from the power booster.
Remove the master cylinder assembly.
Remove the seal from the booster housing. Discard the seal.
Drain the brake fluid.

Installation Procedure

Install the master cylinder assembly with the new attaching nuts.
Install the new seal to the booster housing.

Tighten

Tighten the master cylinder attaching nuts to 18 N•m (13 lb-ft)..

For vehicles with the ABS braking system (as shown), connect the brake lines to the cylinder body.
For vehicles with the non-ABS braking system, connect the brake lines to the proportioning valves.

Tighten

Tighten the brake lines to 16 N•m (12 lb-ft).

For vehicles with the manual transaxle, connect the clip to the clutch hose connection at the master cylinder.

Connect the electrical connector on the reservoir.
Add brake fluid.
Check for leaks and recheck the fluid level.
Bleed the brake system. Refer to Section 4A, Hydraulic Brakes.

Brake Fluid Reservoir

Removal Procedure

Important : Remove the reservoir only when replacing a damaged or a leaking reservoir.

Disconnect the electrical connector from the reservoir.

For vehicles with the manual transaxle, disconnect the clip to the clutch hose connection at the master cylinder.
Gently pry upward with a screwdriver to release the reservoir.
Tilt the reservoir and pull it upward in order to remove it.

Remove the reservoir seals from the master cylinder body.

Installation Procedure

Lubricate the new seals with clean brake fluid. Install the seals into the cylinder body.
Install the reservoir on the master cylinder body. (The ABS system is shown.)

For vehicles with the manual transaxle, connect the clip to the clutch hose connection at the master cylinder.

Add brake fluid.
Raise and suitably support the vehicle.
Bleed the braking system. Refer to Section 4A, Hydraulic Brakes or Section 4F, Antilock Brake System.Bleed the clutch master cylinder. Refer to Section 5C, Clutch.
Lower the vehicle.
Connect the reservoir electrical connector.

Prorortilning Valve

Removal Procedure

Disconnect the brake lines from the proportioning valves.
Remove the valves from the master cylinder body.

Installation Procedure

Important : Since these valves are adjusted in pairs to the correct control range, they must be replaced in pairs.

Install the proportioning valves to the cylinder body.

Tighten

Tighten the proportioning valves to 40 N•m (30 lb-ft).

Connect the brake lines to the valves.

Tighten

Tighten the brake lines to 16 N•m (12 lb-ft).

Raise and suitably support the vehicle.
Bleed the braking system. Refer to Section 4A, Hydraulic Brakes or Section 4F, Antilock Brake System.
Lower the vehicle.

UNIT REPAIR

Master Cylinder Overhaul

Disassembly Procedure

Remove the master cylinder. Refer to "Master Cylinder Assembly" in this section.
Remove the brake fluid reservoir. Refer to "Brake Fluid Reservoir" in this section.
Remove the seal ring from the cylinder bore.

Notice : When removing the retaining ring, avoid damaging the piston or the cylinder wall.

Important : A welding rod or its equivalent can be used in a compensating port to keep the piston pressed down.

Remove and discard the retaining ring from the cylinder body using a suitable screwdriver. (The non-ABS master cylinder body is shown.)

Remove the primary piston. (The ABS master cylinder body is shown.)
Carefully remove the secondary piston assembly and the spring from the master cylinder bore.

Assembly Procedure

Notice : Do not use abrasives in the master cylinder bore. Abrasives can damage the bore.

Important : Rubber parts and retaining rings must be discarded and replaced with new parts

Clean all parts with denatured alcohol or clean brake fluid. Dry the parts with compressed air.

Inspect the master cylinder bore for scoring or corrosion. If scoring or corrosion is evident, replace the master cylinder body.
Lubricate the master cylinder bore with clean brake fluid. (The non-ABS master cylinder is shown.)

Carefully insert the secondary piston assembly bore until the secondary piston contacts the base of the cylinder body. Use a wood or a plastic drift, if necessary.
Insert the primary piston.

Press the pistons into the cylinder bore using a wooden or a plastic drift.

Notice : When installing the new retaining ring, take care not to damage the cylinder bore.

Insert the new retaining ring into the groove in the cylinder bore. (The non-ABS cylinder body is shown.) Remove the welding rod.
Move the pistons backward and forward after installation to check for free movement.

Lubricate the seal ring and insert the seal on the shaft into the cylinder bore. The open side must face outward until the seal rests on the piston.
Install the brake fluid reservoir to the master cylinder. Refer to "Brake Fluid Reservoir" in this section.
Install the master cylinder assembly. Refer to Master Cylinder Assembly in this section
Raise and suitably support the vehicle.
Bleed the braking system. Refer to Section 4A, Hydraulic Brakes or Section 4F, Antilock Brake System.
Lower the vehicle.

GENERAL DESCRIPTION AND SYSTEM OPERATION

Master Cylinder

The master cylinder is designed for use in a diagonalsplit system. One front and one diagonally opposite rear brake are served by the primary piston. The opposite front and rear brakes are served by the secondary piston. The master cylinder incorporates the functions of the standard dual master cylinder, plus a low fluid level indicator and the proportioning valves in the non-antilock braking system. The proportioning valves limit the outlet pressure to the rear brakes after a predetermined master cylinder pressure has been reached.

Notice : Do not use lubricated shop air on brake parts, as this may damage rubber components.

Important :

Replace all the components included in the repair kits used to service this master cylinder.

Lubricate rubber parts with clean brake fluid to ease assembly.

if any hydraulic component is removed or disconnected, it may be necessary to bleed all or part of the brake system.

The torque values specified are for dry, unlubricated fasteners.

Perform all service operations on a clean bench, free from all traces of mineral oil.

Proportioning Valves

The proportioning valves limit the outlet pressure to the rear brakes on the non-antilock braking system after a predetermined master cylinder pressure has been reached. This is used when less rear apply force is needed to obtain optimum braking and is usually found on disc/drum brake configurations. On ABS-equipped vehicles, refer to Section 4F, Antilock Brake System.

Fluid Level Sensor

The master cylinder is equipped with a fluid level sensor. This sensor will activate the BRAKE light if a low fluid level condition is detected. Once the fluid level is corrected, the BRAKE light will go out.