GM Service Manual Online
For 1990-2009 cars only

Vacuum Booster Diagnosis Brakes Grab

Step

Action

Value(s)

Yes

No

DEFINITION: The brakes grab on and off.

1

Inspect the hydraulic brake pipes and hoses.

Are the hydraulic brake pipes and hoses damaged?

--

Go to Step 2

Go to Step 3

2

Replace the hydraulic brake pipes and hoses as necessary. Refer to:

    •  Brake Pipe Replacement

Do the brakes still grab?

--

Go to Step 3

System OK

3

Inspect the fluid level in the master cylinder.

Is the fluid level low in the master cylinder?

--

Go to Step 4

Go to Step 5

4

Fill the reservoirs with the proper brake fluid. Check for leaks.

Do the brakes still grab?

--

Go to Step 5

System OK

5

Inspect the master cylinder seals.

Are the master cylinder seals faulty?

--

Go to Step 6

Go to Step 7

6

Repair or replace the master cylinder seals as necessary. Refer to Master Cylinder Overhaul .

Do the brakes still grab?

--

Go to Step 7

System OK

7

Inspect the master cylinder casing.

Is the master cylinder casing cracked?

--

Go to Step 8

Go to Step 9

8

Replace the master cylinder. Refer to Master Cylinder Replacement .

Do the brakes still grab?

--

Go to Step 9

System OK

9

Look for leaks in the following components:

    • Front calipers
    • Rear wheel cylinders
    • Pipes
    • Connections

Do any of the components leak?

--

Go to Step 10

Go to Step 11

10

Inspect and repair the leaking components as necessary.

Do the brakes still grab?

--

Go to Step 11

System OK

11

Inspect for air in the hydraulic system.

Is there air in the hydraulic system?

--

Go to Step 12

System OK

12

Bleed the hydraulic system. Refer to Hydraulic Brake System Bleeding .

Do the brakes still grab?

--

Go to Step 1

System OK

Vacuum Booster Diagnosis Hard Pedal

Step

Action

Value(s)

Yes

No

DEFINITION: Brake pedal effort is too high when stopping.

1

Inspect for a damaged, collapsed, loose, or open vacuum hose.

Is the vacuum hose OK?

--

Go to Step 3

Go to Step 2

2

Repair or replace the vacuum hose.

Is the brake pedal effort too high when stopping?

--

Go to Step 3

Go to Step 8

3

Inspect for a faulty vacuum check valve or a leaking grommet.

Is the check valve and the grommet OK?

--

Go to Step 5

Go to Step 4

4

Replace the check valve or the grommet.

Is the brake pedal effort too high when stopping?

--

Go to Step 5

Go to Step 8

5

Inspect for a loose or plugged vacuum fitting.

Is the vacuum fitting OK?

--

Go to Step 7

Go to Step 6

6

Clean, tighten, or replace the vacuum fitting.

Is the brake pedal effort too high when stopping?

--

Go to Step 7

Go to Step 8

7

Replace the vacuum brake booster.

Refer to Power Vacuum Brake Booster Replacement .

Is the brake pedal effort too high when stopping?

--

Go to Brake Pedal Excessive Effort

Go to Step 8

8

Verify proper brake system operation.

Does the brake system operate properly?

--

System OK

Go to Hydraulic Brake Diagnostic System Check