Was the Hydraulic Brake System Diagnostic Check performed?

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Go to Step 2

Go to Brake System Diagnosis

1. Verify the customer complaint.
2. Define the type of noise, and when the noise occurs.

Does a hissing noise occur?

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Go to Step 3

Go to Step 4

A normal hissing noise, very noticeable when the vehicle is motionless, occurs when the brake pedal effort is 266 N (60 lb) or more and increases in intensity if the pedal effort increases above this norm or if the operating temperature increases.

Does the hissing noise appear normal?

=/< 266  N (60 lb)

System OK

Go to Step 5

Normal clunk/click/clatter noises occur when you quickly release the brake pedal from hard efforts of 222-444 N (50-100 lb).

Does the clunk, clatter, or clicking noises appear normal?

222-444 N (50-100 lb)

System OK

Go to Step 5

Does the noise occur under any of the following conditions?

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Go to Step 8

Go to Step 6

A moan or low frequency hum noise may be the result of a problem within the power steering system. Refer to Power Steering System Test in Power Steering System.

Was a repair performed on the power steering system?

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Go to Step 11

Go to Step 7

Check the hydraulic brake booster accumulator for proper operation. Refer to Accumulator Leak-Down Test .

Is the hydraulic brake booster accumulator operating properly?

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Go to Step 10

Go to Step 9

1. Obtain a vehicle with a known acceptable brake booster system.
2. Run both vehicles until the engines reach normal operating temperature.
3. In both vehicles, duplicate the operating condition associated with the noise. Listen for the noise.
4. Compare the results.

Does the acceptable system make the same noise?

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System OK

Go to Step 6

Replace the accumulator. Refer to Hydraulic Brake Booster Accumulator Replacement .

Is the repair complete?

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Go to Step 11

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Replace the hydraulic brake booster. Refer to Power Brake Booster Replacement .

Is the repair complete?

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Go to Step 11

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Verify proper brake system operation.

Does the original condition still exist?

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Go to Step 1

System OK