The hood latch mechanism in a car is a simple device. Although most cars are manufactured with similar bonnet release systems, they are individually designed for each make and model. This means that even though they all perform very similarly, they cannot be uninstalled from one make and model and then reinstalled in a different make and model. The overall concept of the mechanism is the same, but the schematics and design of the hood latch system is different on each vehicle.
The hood latch system begins inside the compartment of the car. Located on the driver's side (usually on the left-hand lower corner of the dashboard) is the hood release handle. The hood release handle attaches to a cable which then routes through the dashboard towards the front of the vehicle. The other end of the cable is attached to a secondary latch, which is manipulated by the pulling of the cable (activated by pulling the hood release lever). Only an inch or two is required to pull the secondary latch away from its position, and then the hood pops open. At the front of the vehicle, a safety latch retains the hood. Locating and releasing the safety latch releases its hold on the hood and then the hood is allowed to open.
Components of a Hood Latch System
The hood release handle inside the vehicle is made of plastic and is attached directly to the hood latch cable. The cable has a protective outer lining to prevent corrosion of the cable where it is exposed to the elements. The cable is designed to move inside the lining back and forth to accommodate the pulling and releasing motion of the handle and the secondary latch. The opposite end of the cable is attached to the secondary latch, usually near the bottom. When tension is applied to the cable from the hood release handle, it pivots the secondary latch, which pulls away from a retaining seat located under the hood. By design, the secondary latch then releases the hood a few inches before a safety latch takes over. The safety latch is integrated in the hood latch system in case of accidental release of the handle inside the passenger compartment during operation of the vehicle. Without the safety latch, the hood would be susceptible to flying up and then back towards the windshield, blocking the driver's vision, and most likely causing extensive damage to the hood, the hood hinges, and the windshield.
The safety latch has a release lever which pivots slightly by moving it, which then releases the safety latch from its seated position of the hood. Most safety latches require release with no tension on the hood. This means, you most likely have to press the hood down slightly back in the closed position, thus taking the slight pressure off the safety latch to manoeuvre it and release it from the seat. Once that is done, the hood is free to open. Many bonnets use a prop rod integrated with the vehicle. The prop rod is located on the upper frame of the front or side rails and attached at the bottom. A small clip holds the upper end of the rod in place. Release the rod from the clip, swing it upward and locate its seating position (usually marked) on the underside of the hood. Other models may have the prop rod attached to the underside of the hood and the seating position located on the upper frame rails. High-end vehicles are now using hydraulic hood shocks to automatically open car bonnets and replace the bonnet prop rod altogether.
Maintenance to the Hood Latch Components
After many uses and normal wear and tear, the hood latch mechanism has common areas of deterioration. The pull handle, often made of plastic can simply break. The cable can seize up inside the lining (usually on the end attached to the secondary latch where it's exposed to the elements). The secondary and safety latches can dry up being exposed to the elements and not release properly or may not return to the closing position require to close the bonnet properly. Although a hood release latch may allow you to open a car bonnet, if it is not functioning properly, it may prevent you from closing it. White lithium grease and regular maintenance are the two best friends a hood latch system has. A small amount of grease on each end of the cable (the interior side of the cable is protected against the elements of weather and deterioration so usually require little maintenance) to lubricate it and prevent it from seizing up inside the lining usually keeps the cable working well. If you wait until the cable is sticking or is seized altogether, you most likely will be too late for the maintenance of the cable and replacement may be required. White grease on the secondary and safety latches is also strongly recommended to keep the latches swinging on the riveted hinges.
Both the secondary and safety latches also integrate a tension spring. Keeping the springs lubricated helps them restore their tension. Keeping these components lubricated during every oil change will help provide longevity and reliability to the hood latch system.