How to Check a Brake Power Booster

How to Check a Brake Power Booster

A brake power booster is a vacuum operated device which reduces the effort needed to press the brake pedal and apply the brakes. In most cases the vacuum is created by the running engine and air is drawn from the booster through a rubber hose connected to the intake manifold. Diesel engines do not produce much vacuum and may employ a vacuum pump. High pedal effort and poor braking action indicate a problem with the booster or the vacuum system.

Things You'll Need
Vacuum gauge


Instructions
Depress the brake pedal repeatedly with the engine off.

Continue to hold the brake pedal down and start the engine. The brake pedal should be pulled down slightly after the engine starts. A problem with the brake booster or the vehicle vacuum system is indicated if the pedal does not pull down slightly.

Connect a vacuum gauge to the hose from the engine to the brake booster and start the engine. A reading of 16 inches or more of vacuum rules out a problem with the vacuum system and indicates the need to replace the brake booster.

How to Bleed Calipers on a 2008 Jeep Wrangler

How to Bleed Calipers on a 2008 Jeep Wrangler

Jeep produced the 2008 Wrangler in the X, Unlimited X, X RHD and Sahara trim levels. All of the Wrangler models were powered by a 202-horsepower, 3.8-liter, fuel-injected V-6 engine. The brake system used a vacuum booster to increase braking power while reducing effort at the pedal, and an anti-lock brake system for safety and improved traction control. Air bubbles trapped in the brake system can lead to spongy brakes and reduced braking performance, and must be purged to restore the brakes to their proper feel and performance.


Things You'll Need
Shop rags
Mopar DOT 3 Brake Fluid, meeting SAE J1703 requirements
Clear vinyl tubing
Open-end wrench
Clean container
Assistant


Instructions
Wipe the top of the brake fluid reservoir with a clean shop rag to remove any road grime that could contaminate the system. Remove the reservoir cap. Add fresh brake fluid until the fluid level reaches the "Full" mark. Pour some fresh fluid into a clean container.

Install a short length of clear vinyl tubing over the right rear caliper bleeder valve nipple. Lead the loose end into the clean container, and submerge the end of the hose in the brake fluid. Fit a six-point, box-end wrench onto the bleeder valve.

Instruct your helper to apply and hold steady pressure on the brake pedal, then open the bleeder valve approximately 1/2 turn to bleed the line. Close the bleeder valve and instruct your helper to release the brake pedal. Observe the fluid stream in the vinyl tubing, and repeat the bleeding process until the stream is clear and free of air bubbles. Top off the fluid level in the reservoir.

Repeat the process on the left rear, right front and left front calipers, in that order. Top off the reservoir between each wheel -- don't let it run dry, or you'll have to start all over. Test the brakes in a safe environment before entering traffic.



Tips & Warnings

DOT 4 brake fluid is an acceptable substitution if DOT 3 fluid is not available.
Do not shake up or agitate the brake fluid bottle before using the fluid. The fluid can hold air bubbles in suspension and make it difficult to bleed the brakes properly.