Mechanics Corner - May 11
“Power Steering Troubles”
By Mike Godwin
This month’s article started life as a question from a fellow MNW member. Seems the Mustang in question has a bad habit of repeatedly leaking Power Steering fluid. The car had been repaired several times by a reputable shop in the local area, but the owner noted that about three months after the repairs, the car would return to the unacceptable practice of leaking fluid. It seems that the fluid would fill the boot, which covers the actuator rod (slave cylinder), then leak onto the ground.
We exchanged several emails, and established a history of the repairs and a complete list of the parts replaced. As I am far from being overly familiar with Power Steering systems, I started beating the bushes for information. One of those called upon for ideas and suggestions of possible cures, was our very own Scott Robinson. Like me, Scott had experience replacing defective parts, but not troubleshooting an entire system. He did offer a few suggestions, and pointed out a test printed in the 1966 Mustang / Comet repair manual. Some others were contacted, but far less helpful. So THANKS Scott—we appreciate your input.
Step one for me was to get smarter about Power Steering systems in general. The biggest piece of the system that nearly everyone would recognize is the Power Steering Pump. These pumps are referred to as being of the reciprocating type. By definition, that means that the faster you spin the pump, the greater the pressure becomes. Of course, unlimited pressure is not obtainable by any system, so to prevent over-pressurizing the Power Steering system on the car, a relief valve is incorporated into the system. In the case of first generation Mustangs, this valve is always located in the Control Valve. This part is often called a Master Head or Power Head. It is sold as a separate part, and bolts onto the end of the actuator rod and the drag link. The relief valve prevents the over-pressurization by allowing some of the high pressure fluid to be fed back into the high pressure side of the system. At the same time, this valve supplies the low pressure side with adequate fluid to keep the reservoir in the pump full of fluid. The Control Valve determines which direction the car is trying to turn and supplies high pressure fluid to the actuator rod.
As my company produces Remotely Operated Vehicles (ROV) for numerous applications, I turned to the experts in hydraulic arms and the Mechanical Engineering talents that reside in that division. One of the most common causes of leaks in hydraulic systems I was told, is kinked hoses or improperly seated hoses. Nearly all Power Steering systems use a fitting called a 37 degree pressure fit style fitting. These fittings have a machined mating surface that protrudes on one surface and is indented on the mating surface. The fitting must be clean and damage-free to work properly. I was also told that if the fitting is not damaged too severely, that a crush cone made of soft metals like copper, can be installed between the two mating surfaces to solve a leak.
The next item we were instructed to check on, was the slave cylinder. Specifically, we were instructed to place the wheel in the full lock position in each direction. We were to watch for any obstruction and to note if the effort to turn the wheel changed as it traveled from lock to lock. Next, we were to lay a straight edge against the exposed piston rod and look for any deflection in the rod. A bent rod could cause the system to bind and require greater pressure to operate the front wheels.
The car owner and I did not have an opportunity to get together and try out some of these ideas before the car was sent to a repair shop for a brake problem. While in the shop, the slave cylinder was replaced and the owner reports that three weeks have passed now without a leak. Looks like we found a solution to this problem and the car once again has become a well-mannered Pony. So with a little research and exchange of ideas, the owner once again has a car that does not leak fluids onto the ground or garage floor.
Found it interesting that Ford even installed a sensor in the high pressure Power Steering lines for many applications that would increase the idle speed when the switch closed. The sensor would sense the increase of pressure caused when a Power Steering system is turned into the stops in one direction. To prevent the engine from stalling, the Engine Control Module would increase the engine RPM slightly. Imagine trouble-shooting an engine that repeatedly stalls and not having that little piece of relatively obscure information available.
So should you find a red-colored oily substance under your car, a quick check of the Power Steering fluid level would be a good starting point. Don’t forget that the dip stick has a level for cold and a different level for a hot reading. Adding too much fluid can cause damage, as the Power Steering system is a sealed system. Not completely sealed like our hydraulic brake lines, but still a contained system. In the Power Steering world, the fill tube will act as a vent if the system is over-pressurized. Think of this as the overflow on your radiator. Difference is, that the Power Steering unit does not have a reservoir to catch the discharged fluid.
If your fluid level is low then it is very likely that the fluid on the garage floor is from the Power Steering system. Start by checking all the hoses for kinks or hoses that seem to be at odd angles. Next, look at each point that the hoses connect to the components and make sure that no signs of leakage are present. One method is to wipe the hoses with a white paper towel or light colored shop towel. Normally for me, the result is the sacrifice of the oldest car show T-Shirt that is within reach.
Please, whatever you do, don’t pour a can of the magic stop leak material into your Power steering system. You are far better off actually finding the cause of the leak and repairing the problem than throwing a band aid type fix at the problem.