Dandy. If it steers easier one way, you know the pump is working.
Two things can happen in the rack assembly. The most common failure is grooves worn in the housing where the spool valve sits. That's the valve that's connected to the steering shaft, and it directs the pressurized fluid flow to one side or the other of the built-in power piston. There's four teflon sealing rings, similar to little piston rings on that valve. Over time those rings wear grooves into the housing and allow pressurized fluid to bypass the valve rather than put their pressure on the power piston. The fluid just goes right from the pump, around the valve, and right back to the reservoir and pump without doing any work. General Motors had a really huge problem with that in the '80s and they came up with a real cheap fix to squeak those cars out of the 50,000 mile warranty. When the problem occurred again a few months later, the owners had to pay for the proper repair. That was the first time I realized how customer-unfriendly and greedy GM is.
The proper fix is to replace the rack assembly with a rebuilt unit. Rebuilt racks are MUCH less expensive than a new one from any manufacturer and the major rebuilders bore out the housing and insert a stainless steel liner that won't get those grooves worn into it. The housing is soft aluminum which wears away easily. GM knew that was what was happening with their cars, but the proper fix was too costly in their mind. Perhaps 5 percent of the wear was on the sealing rings and that was enough that a new valve assembly with those new rings made the problem go away for a little while, but it was the 95 percent of the wear in the aluminum housing that didn't get addressed by that "fix". They knew the problem was going to come back. They just hoped not until it was out-of-warranty.
Toyota is not known for having this problem but it can happen to any original rack assembly with high miles. A different, less common problem has to do with the spool valve coming apart. As a former suspension and alignment expert, I only experienced that two or three times over 16 years, but it can be very irritating to drive the vehicle when that happens. Sometimes the steering wheel turns normally, and the next time it turns hard and then all of sudden breaks free and turns too far. That will affect steering both ways and will start out being intermittent. Play between the inner and outer parts of the spool valve cause the fluid ports to open sometimes and not others as that valve is turned. Most of the time when that valve is the problem it will be accompanied by fluid leaking from the housing right where the steering shaft connects to it. In one case I saw that dump a lot of power steering fluid on the driver's floor. That was on a Ford. There was just a little hint of fluid seepage when it happened on my ******'s '95 Grand Caravan. If you see wetness on yours under the dash where the steering shaft connects, you'll know you need a new rack and pinion assembly. If there is no sign of leakage, that doesn't mean the valve can't still be defective.
To add another clue and potential symptom, when you turn the steering wheel, you're only turning the inner part of the spool valve, nothing else. That causes two ports to line up and allow fluid to flow. Pressurized fluid flows into the main housing and pushes on the power piston which pushes on the steering linkage. Fluid on the other side of the piston gets forced out the second port and back to the reservoir. That moving power piston and rack is attached to the outer part of the spool valve and turns it to close it. That stops the movement of the steering linkage unless you turn the steering wheel further. That valve remains open as long as you keep turning the steering wheel. When you stop turning the wheel, the spool valve catches up and closes. In the case of my ******'s van, when that valve started coming apart, at times it would not close. That caused the steering system to keep on turning after she had let go of the steering wheel. There is nothing in the entire system that can cause that other than a defective spool valve so diagnosis is real easy. While that is a very dangerous condition, you will have plenty of warning before that happens. That valve will not suddenly break without warning and surprise you. Except in a few instances, repair parts are not available to us. The only way to fix this is by replacing the entire rack and pinion assembly. Fortunately, a quality rebuilt unit costs about one fourth of the cost of a new one, and many come with lifetime warranties as long as you insert the filter they include into the return hose. When I left the dealership in '99, rebuilt racks cost around $125.00 to $150.00 but I think they are even less expensive now.
You'll have to look at your vehicle to see how hard it is to replace to decide if you want to do it yourself. It lives right in the front of '90s Dakotas and can be replaced in 20 minutes. It is buried in the miserable Stratus and takes over 3 1/2 hours to replace it. It will be almost impossible without that car on a hoist. Regardless if you replace it or you have a shop do it, the vehicle will need an alignment because the new rack is part of two alignment adjustments.
Monday, December 26th, 2011 AT 10:30 PM