Question 1

How to diagnose and repair potential vacuum leaks in the Brake Booster of a power brake system on Nissan 240sx?

Accepted Answer

Power brakes can be deemed to work in the same way as non-power brake systems but with the difference arising from the way master cylinder piston is actuated with assistance from vacuum diaphragm situated at the front of the master cylinder. This diaphragm helps the driver apply the brakes; it lessens the amount of force and space through which the brake pedal has to travel. The vacuum diaphragm housing is attached to the intake manifold and is connected with the help of a vacuum hose having a check valve when ever there is low manifold vacuum and thus the brake assist vacuum is not lost. When the brake pedal is pressed, the vacuum is cut-off, thus allowing pressure from the atmosphere to be applied to one side of the diaphragm and this in-turn pushes the master cylinder pistons out and applies the brakes. The release of the brake pedal returns the vacuum on both sides of the diaphragm, and return springs take the diaphragm with the master cylinder pistons to their initial position. When the vacuum does not build up, the connection between the brake pedal rod and the end of the master cylinder actuating rod comes into play and the vehicle's brake is applied mechanically as one presses the brake pedal. The dysfunctions regarding the hydraulic and mechanical mechanisms valid for ordinary brake systems also apply to power brakes and one can examine them as causes if the problems are recurrent. To check for a system vacuum leak rev the engine up to idle and do not step on the brake pedal for one minute or more and shuts down the engine and waits for one more minute. Closely inspect assist vacuum by step on and off the brake pedal several time, the light pressure will decrease the pedal travel if assist vacuum is there. When no vacuum is registered, the inference is that air is probably entering the system. For systematic operating test-turn off the engine and pump the brake with the supply vacuum until the light exhaustion after this apply steady pressure to the brake pedal. Situation of turning on the vehicle engine together with building up pressure should make the brake pedal depress downwards if the above system is properly functioning. Besides, power brake systems may also be checked for hydraulic leaks as the ordinary brake systems may be.

Question 2

How to properly check the functionality of the Brake Booster, and what specific pedal responses should you observe during the tests on Nissan Altima?

Accepted Answer

For close up images of the brake system, the brakes should be checked each time the wheels are changed or when a defect is assumed to be present, signs suggesting that there could be a problem are the car pulling towards the side when the brake is stepped on or any of the following brake sounds which are squealing or dragging, brake pedal goes down very far or 'jams', pulsating brake pedal, or any signs of brake fluid loss. The disc brake pads have wear-rod incorporated into it that squeals when worn, correct them immediately to ensure they do not harm the discs. Start with the wheel lug nuts and unscrew them, then chock the vehicle and jack it up and place it on jack stands and remove the wheels. Every caliper has two pads which are visible through the inspection holes, by touching thickness is checked; if the lining material is lower than the required thickness then it should be repaired. If for some reason it is hard to judge the thickness, then take the calipers and pads off, soak it in brake cleaner and them put it back to check on the thickness again. Check the thickness of disc using a micrometer and replace any disc that has a thickness less than the minimum standard and look at the disc for scores or gouges. Before re-fitting the wheels, check all brake flexi & pipes for any damage, sharp edges or near to any moving parts, and repair or replace if required. Press the brake booster while being in the driver's seat and carrying out tests on the pedal during start, during multiple presses and after shutting down the car. There can be occurrences where the pedal does not respond as it is supposed to, in such cases, the brake booster might require repair. With the parking brake, pull it normally, count how many clicks you were able to achieve, increase or decrease the rachet handle, or better yet, position the car up on a hilly area and see if the parking brake can keep the car from moving.

Question 3

How to inspect and maintain the brake system, including the disc brakes, brake booster, and parking brake on Nissan Murano?

Accepted Answer

For close-up pictures especially of the brake system, check the brakes every time the wheels are off or where there is reason to believe in a defect. Signs associated with brake system problems include an occurring of pulls to the side when the brake is pressed, noises such as squealing or scraping when the brakes are used, change in the brake pedal travel and thickness, pulsation and brake fluid leaks. Disc brake pads come with wear limiting sensors which emit a high pitched squealing or scraping sound when the pads are at the replacement level, hence must be replaced to enable freedom of further wear which would harm the discs. First, free the wheel lug nuts, then safely jack up and support the vehicle by means of jacks and jack stand and finally unbolt the wheels. Measuring the brake pad thickness, this can be done on the outer pad at both ends of the caliper and on the inner pad through the inspection hole in the caliper body and determine the thickness of the brake pads. If the thickness of any brake pad is less than the said dimension, then all the pads have to be changed. If this is not possible, take the caliper(s) and pads out for further examination, either using a brake cleaner wipe, or using a micrometer to double check thickness. Use the micrometer to check the disc thickness and service life; any disc measuring thinner than the specified minimum should be replaced; also look for scoring, gouging, or burned spots on the disc, and resurface it if such flaws are noticed. Before refitting the wheels, it is advisable to inspect all brake pipes and flexible hoses for signs of distortion, corrosion, cracks, and leakage to guarantee that they are not subjected to sharp surfaces or moving members. For the brake booster check, sit in the driver's seat and perform a series of tests: With the brake fully pressed down turn on the engine then check if the pedal goes down slightly; Press the brake pedal several times while the engine is running to determine if the travel distance changes; allow the brake pedal to be pressed down for a full 30 seconds after turning the engine off and check if it sinks or rises; and finally start the engine and then press the brake pedal several times to diagnose if the travel decreases. If the result is otherwise, then the brake booster should be repaired or changed out as necessary for correct function. For the parking brake, engage it with normal force, and make sure it goes notches to the required level if it does not, adjust it. Or park the vehicle on a steep gradient with your parking brake engaged and transaxle in Neutral and apply the emergency brake as a test to see if it will not move; if it rolls adjustment will be needed.

Genuine Nissan Brake Booster

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Nissan Brake Booster Assembly

Nissan Brake Booster Assembly

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