How to Replace the Cruise Control Vacuum Switch

Cruise control slows down when the vacuum release switch is activated. It fails if the cruise control is deactivated automatically or does not keep the speed.

Older cars from before the advent of electronic control modules used mechanical components to perform functions that are now controlled by electronics and supercomputers. One of the best examples of old technology providing luxury features was the use of a vacuum control that activated and deactivated the cruise control feature.

Decades ago, the cruise control vacuum switch was an integral part of the cruise control system. Once the cruise control was engaged, the negative pressure created by the vacuum system opened and closed the mechanical switches that controlled the cruise control system. The main vacuum switch was located on the cruise control servo and maintained a constant vacuum pressure after the cruise control was engaged. This action froze the throttle lever at a predetermined position to establish a "cruising speed".

When the driver wanted to slow the vehicle, he would either press the decelerate button on the steering wheel or press the brake pedal, which released the vacuum in the servo. The vacuum release switch is known as the cruise control vacuum release switch. Although it is a secondary backup system for disabling cruise control, it is an incredibly important safety component and should be replaced if damaged.

The cruise control vacuum switch is designed to maintain vacuum pressure until the brake pedal is depressed. Sometimes this switch will wear out and leak, preventing the cruise control from maintaining vacuum pressure and making the cruise control ineffective or inoperable. As a rule, when the vacuum switch fails, a hissing sound is heard from under the dashboard near the brake pedal or from under the hood. Due to the fact that each vehicle manufacturer has designed their cruise control systems differently, the location of the cruise control vacuum switch or secondary locking devices varies.

• Attention: We will discuss the steps to remove and replace the most common vacuum cruise control switch located inside the servo. If the vehicle has a servo-mounted vacuum switch, it is recommended to replace the entire servo assembly, as the process of rebuilding a servo is incredibly difficult, time-consuming, and more expensive than simply replacing the old assembly with a new system.

Part 1 of 3: Identifying the Symptoms of a Faulty Cruise Control Vacuum Switch

Older cruise control systems are made up of several components that must work together in order for the system to activate and deactivate. Cruise control on vehicles manufactured prior to 1996 contains backups that ensure that the system is deactivated in the event of a system failure. The cruise control vacuum switch is one such back-up system.

If the cruise control vacuum bleed switch is not working, it can be very difficult to determine that this component is defective. However, when this component is not working properly, you may hear a hiss near the pedals. A faulty vacuum switch will also display the following warning signs:

• Cruise control does not hold speed: if the vacuum release switch is broken, it will not be able to maintain vacuum pressure inside the servo that holds the throttle in a predetermined position. When the driver sets the cruise control, it will hold speed for a very short time, but a vacuum will leak, causing the throttle to close slowly. On older vehicles, this symptom is usually caused by a leak in the vacuum system.

• Cruise control won't turn off: If the vacuum bleed switch is clogged or broken, this can also affect the cruise control's ability to turn off cruise control after it has been set. While cruise control can be turned off by turning the system to the "OFF" position (which bleeds vacuum pressure through the main line), most drivers turn cruise control off by pressing the brake (which causes the vacuum bleed switch to operate). If this is a symptom, you should replace the servo and trace all vacuum lines, as this will lead to a serious safety breach.

• Cruise control disengages automatically while driving: If you are driving on the road with cruise control on and the cruise control disengages without depressing the pedal, this could also be a fault caused by a permanently open vacuum bleed switch.

Part 2 of 3: Replacing the Cruise Control Brake Switch

Replacing the cruise control servo is the best option if there is a problem with the vacuum switch, as it is nearly impossible to find the components on their own and repairing the servo is very time consuming and tedious.

Necessary materials

• Socket wrench or ratchet wrench
• flashlight
• Flat blade screwdriver
• Cruise control servo replacement
• Replacement of vacuum lines
• Safety glasses

Step 1: Disconnect the car battery. The first thing to do before replacing any electrical component is to disconnect the power supply. Locate the vehicle's battery and disconnect the positive and negative battery cables before continuing.

Step 2: Find the servo. Vacuum type cruise control systems use a servo connected to a vacuum reservoir.

The servo itself is usually attached either to the firewall or to the inner fender on the driver's or passenger's side. If the vacuum bleed switch inside the servo is broken or damaged, it's easier and cheaper to replace the servo than trying to rebuild it.

Step 3: Visually inspect the vacuum lines attached to the servo.. In many cases, the problem with vacuum type cruise control is that the vacuum line has a hole, wears out, or is disconnected. Before you waste time replacing a servo, visually inspect all vacuum lines attached to the servo and route them to the components they are attached to on the vehicle. If the vacuum line is damaged or disconnected, troubleshoot the issue first and have the cruise control checked to see if the issue is resolved.

Step 4: Remove any dashboard covers or other covers that are in the way. Sometimes the servo is located under the dashboard and attached to the firewall. To free up space, remove the plastic or metal cover that is on top of the engine compartment. See your vehicle's service manual for specific instructions.

Step 5: Remove the bolt that secures the servo to the bracket.. After you have completed the visual inspection of the vacuum lines, remove the servo. To do this, first remove the bolt that secures the servomotor to the vehicle's support bracket or firewall. This bolt is usually 8mm in diameter, so use a socket, extension, and ratchet to remove the bolt.

Step 6: Slide the servo off its mounting tabs. Most servos are held in place by a bolt and studs that are attached to the servo inserted into two holes or lugs on a bracket or firewall. Carefully slide the servo off these tabs and continue to the next step if applicable.

Step 7: Removing the Wiring Harness. Some vacuum powered cruise control systems are hybrid, meaning they are also powered by electric lines. In this case, the servo has a wire harness attached to the bottom of the servo. Remove this harness, if applicable, and proceed to the next step.

Step 8: Mark all vacuum lines connected to the servo.. There are two vacuum lines on the servo, one to the vacuum tank and the other to the brake switch. Be sure to label each one before removing the vacuum lines.

Step 9: Remove Vacuum Lines.

Step 10: Remove the Throttle. The servo has a throttle cable attached to a nipple on the front of the servo. Remove this cable.

Step 11: Remove the servo from the car. Once all lines are disconnected and set aside, remove the old servo from the car.

Step 12: Install the vacuum lines on the new servo.. After you have removed the old servo, reinstall the vacuum lines as noted to the same connections as on the old servo.

Step 13: Connect the wiring harness.

Step 14: Insert the New Servo into the Tabs.

Step 15: Reattach the bolt that secures the servo to the firewall or bracket.. Make sure the bolt is fully tightened.

Step 16: Replace all caps. Be sure to replace whatever you removed to gain access to the servo.

Step 17: Replace battery cables. Connect cables correctly.

Part 3 of 3: Test drive the car

After replacing the servo, check if the repair of the vacuum switch was successful during a test drive. If you are having trouble turning off cruise control after a certain period of time, check the vehicle for at least that same period of time. Here are some tips on how to take a test drive.

Step 1: Start the car. Let it warm up to operating temperature.

Step 2: Move the cruise control button to the "on" position.. See if it lights up on the dashboard before driving. As soon as the cruise control light comes on, you are ready to test the car.

Step 3. Take your car to the test track.. Accelerate to highway speed.

Step 4: Set cruise control to 55 or 65 mph.. After adjusting the cruise control, depress the brake pedal lightly to ensure that the cruise control has disengaged. This tests the vacuum switch.

Step 5: Reset cruise control again and drive 10-15 miles.. Make sure cruise control does not automatically turn off.

If you have read these instructions and are still not 100% sure about completing this repair, please contact one of your local AvtoTachki ASE certified mechanics to come to your home or work to perform the cruise control brake switch replacement for you. . .