The pneumatic side of the Ford air suspension is where most problems begin. Understanding the consumable nature of some components can help prevent major expense.
Ford rear air-ride suspension is an electronically controlled pneumatic system. The previous Detailed Topic discusses the electrical portion of the system. This article concentrates on the air operated components and how they work.
A definition of pneumatic is, operated by air pressure. To help understand potential problems in the Ford air suspension, it helps if we consider the nature of air.
Air contains moisture and we call this humidity. When we compress air, the humidity per volume increases. With the increase, water releases from the gaseous portion. This water will attack the metal components in the system causing corrosion.
The air suspension dryer
Ford uses a dryer, containing a desiccant to remove the moisture that the compressor draws in. This works well, but in time we deplete the desiccant and it no longer functions. When this occurs, corrosion begins and expensive problems follow.
Two factors speed desiccant failure, how much air passes through the dryer and the humidity of the air. Leaks in the system will drastically increase the air needed. A leaking system will soon deplete the desiccant and major problems occur. In an area of high humidity desiccants fail sooner. Replacing the dryer is inexpensive and can prevent many problems.
The air springs
A rubber bag on each side of the rear suspension provides variable lift, depending on the air pressure within. The bag folds on itself and this is the secret to the lift. Air pressure pushes the ends of the bag apart and the fold decreases. When we reduce pressure, the fold increases and the bag becomes shorter.
An original equipment manufacturer or OEM Ford bag is very durable, but as with any piece of rubber, they have a life. In time the rubber dry-rots and cracks. The normal life of OEM Ford air springs is around ten years. Some air springs will last much longer and a few may fail sooner. Most commonly, small cracks form in the folded area of the bag. These cracks leak air and the pump has to run more often to replace it. This soon exceeds the expected duty cycle of the pump and failure occurs.
The most common symptom of leaking air bags is a vehicle that squats in the rear when it sits without running. Another system is a compressor that cycles often. It is far better to realize these bags are consumable and not wait for symptoms.
Bags are easy to check with a soap and water solution. Any bubbles that form show the bag is leaking and we need to replace the bag. After about eight years, periodic inspection is a wise precaution.
Leaking bags are easy to replace and this prevents more expensive problems. With leaks that have existed more than a few days replacing the dryer on the air compressor is best. This precaution can prevent many future problems by keeping moisture out. In high-humidity areas, replacing the dryer every ten years is also a good precaution.
OEM and aftermarket air bags
Original equipment Ford air bags are very durable and fit perfectly. Using the original part insures proper ride, operation and a long life. Aftermarket replacements are also available at lower costs. The quality of aftermarket parts can vary drastically and many are simply cheap imported knock-offs. If the primary concern is price, aftermarket bags provide a lower priced option.
They also produce kits to convert air suspension to steel springs. This defeats the purpose of the wonderful engineering that goes into computer-assisted air-ride.
Conversion kits are much like buying a beautiful home and tearing down half to save on the price of painting it.
Conversion kits can destroy handling, ride and may result in warning lights and other problems. These kits are a butcher approach to an otherwise simple problem. Repairing the air system is far smarter.
The solenoid valve
At the entrance of each air spring, a solenoid valve controls flow of air in or out. When the solenoid is closed, the bag is shut off from the rest of the system. To raise the vehicle, the vehicle dynamics module or VDM turns the compressor on and opens the rear solenoids. Air flows into the bags and the vehicle rises.
To lower the vehicle, the VDM opens the solenoids at the bags and another solenoid valve in the pump. They do not turn the pump on and air flows out of the bags and through the solenoid valve in the pump. This causes the vehicle to lower in the rear.
Replacing the solenoid is not necessary when we replace the bag. We should replace the O-rings on the solenoid every time we remove it.
Releasing the air lines
Plastic pipes transport air between the air springs and the compressor. To retain the air line, they use a special fitting. A small barb in the fitting digs into the line, to hold it in place, and O-rings in the fitting seal it.
Pressing in on the shoulder of the plastic retainer, allows the barb to release. While holding the collar in with one hand, we use the other to pull the line free. If the line is stubborn, pushing in on it and turning slightly may help.
Fashioning a small tool from a flat piece of metal is easy. Cut a slot, the size of the line in one end. Releasing the fittings may be much easier with such a tool.
Prevention is the secret to trouble free and low cost air suspension operation. Lincoln and Ford products with this system are checked in the General Inspection. With this simple precaution the air suspension will provide a great ride and last the life of the vehicle.