Brakes feel soft and won't lock up?

Hi,

There are two bolts that hold the brake master cylinder to the brake booster. Take a look through this link. It shows how in general one is replaced. You can use this as a guide. It also explains bench bleeding a new master cylinder which will need done.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Here are the directions specific to your vehicle. The pics below correlate with the directions.

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2005 Chevrolet Aveo L4-1.6L VIN 6
Master Cylinder Replacement
Vehicle Brakes and Traction Control Hydraulic System Brake Master Cylinder Service and Repair Procedures Master Cylinder Replacement
MASTER CYLINDER REPLACEMENT
Master Cylinder Replacement

Removal Procedure

pic 1

1. Disconnect the electrical connector from the reservoir.

pic 2

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

pic 3

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

Installation Procedure

pic 4

1. Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Service Precautions.

Install the master cylinder assembly with the new attaching nuts.

2. Notice: Refer to Fastener Notice in Service Precautions.

Install the new seal to the booster housing.
Tighten the master cylinder attaching nuts to 18 Nm (13 ft. lbs.).

pic 5

3. For vehicles with the ABS braking system (as shown), connect the brake lines to the cylinder body.
4. For vehicles with the non-ABS braking system, connect the brake lines to the proportioning valves.
Tighten the brake lines to 16 Nm (12 ft. lbs.).
5. For vehicles with the manual transaxle, connect the clip to the clutch hose connection at the master cylinder.
6. Connect the electrical connector on the reservoir.
7. Add brake fluid.
8. Check for leaks and recheck the fluid level.
9. Bleed the brake system.

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I hope this helps. Let me know if you have other questions.

Take care and God Bless,
Joe