Power Steering Basics and Stories

We Need the Power, Cap’n!

 

Some folks will drive vehicles for many a mile with inoperative power steering or brakes, and while the exercise they get that way builds muscle mass, it’s anything but safe, and parking maneuvers in a crowded lot are murderously difficult.  Once my extremely self-reliant aunt was driving an old Buick that had suddenly lost its power steering and she had angled across two parking spaces because it was the best she could do – and when an angry motorist shouted a question as to why she didn’t take three parking places while she was at it, my always dignified and unflappable aunt simply replied that the two parking places she had would do her just fine.

 

Which Way and How Much?

 

There was a time in my early career as an automotive professional that I believed I could fix anything, and in many cases, I was right. After all, we rebuilt power steering racks as a part of a recall when I worked at the Mazda dealer.  But the exuberance born of too many successes in coloring outside the lines can lead to a smack-down.

One hot summer day about 30 years ago I drew a work order on an early seventies Mustang with power steering trouble – and I don’t remember the original write-up, but I do remember making the discovery that a person without sufficient training shouldn’t tear a ball nut steering gear down to the bare parts and reassemble it expecting it to work right.

Just because I had successfully fixed the power steering systems on so many tractors and forklifts, I figured I could whip this one too. As it was, I got things so out of whack on the spool valve adjustment that whenever the engine was started, the steering wheel would whirl all the way to the right so hard that you couldn’t force it back to the center and for the life of me I couldn’t figure out how to fix that; I repeatedly tried to adjust the spool valve but it was no use.  After burning most of a day on that one, the decision was made to replace the steering gear with a used salvage yard unit and I had egg on my face.  In the years after that I replaced some pitman shaft seals and whatnot, but I never attempted a total steering gear rebuild again – after all, a replacement gear doesn’t cost all that much and the repair is finished a lot sooner.

On any kind of power assist, whether brakes, steering, or whatever, the control part of the system has to know when power assist is necessary, and in the case of steering, it needs to know which way that help needs to be directed. The same is true of electric power steering, and there is a very sensitive torque sensor built into the column on the hybrid vehicles Toyota makes, and it is that input that triggers the electric motor to muscle up.

On hydraulic rack and pinion systems, power steering pump sends fluid pressure to a spool valve that is connected to the steering wheel via the column; that spool valve is triggered by steering motion to direct the fluid. And there is sealed flange attached to the steering rack that travels inside a polished bore in the tubular steering gear housing. Each end of the steering rack is attached to a tie rod with a ball socket, the opposite end of each tie rod connected to the spindle arm so as to turn the wheels on their axes.  Fluid directed to one side or the other of the rack’s internal sealed flange provides the assist. Rubber accordion style boots on each end of the assembly protect the rack from dust and moisture, and the only thing that is supposed to be in those accordion boots is air, which, in many cases is transferred from boot to boot through a small tube.  Fluid dripping from these accordion boots on the end of the rack assembly means the rack is leaking internally and needs to be resealed or replaced, and some steering racks are extremely difficult to replace.  These boots obviously need to be replaced if somehow ruptured.

 

What to Do

 

Power Steering pumps produce between 1200 and 2000 pounds of pressure to do their work, and there is a specially designed flow control valve just inside the pressure outlet fitting.

When the power steering pump isn’t spinning fast, such as during parking maneuvers, not as much fluid flow is necessary, but high pressure is still required. Be that as it may, the flow control valve’s internal orifices and springs act to bypass some of the pump pressure internally so that the pump’s output pressure is slightly less than what the pump is producing, and it is this pressure that is delivered to the steering gear.

When the pump is spinning faster but with little or no steering activity (straight driving), fluid flow is increased, which reduces pressure at the pump outlet, and excess fluid is directed back to the pump inlet by the flow control valve. One way or another, the flow control valve’s springs and orifices are tuned to provide needed steering assist.

With the steering wheel held at full-lock and the assist chambers in the steering sector/gear are fully pressurized, the flow control valve acts as a bypass to prevent the pump from stalling out completely.  If the flow control valve malfunctions, you may see a quietly spinning pump that is full of fluid but producing no pressure at all. Obviously, replacing the pump is the most viable option – but I have on occasion replaced flow control valves when they were available. The problem is that in some cases they’re stuck in the bore and are too much trouble to remove. There is a test procedure using a pressure gauge to test the flow control valve, but it’s a pedantic test that’s too much trouble to fiddle with and we won’t waste time with it here.

Power steering lines have distinctly bent metal tubes where they connect to the steering pump and the gear and since the pump is on the engine and the gear is frame-mounted, the fluid travels through high pressure rubber hose en route for flexibility.  Some power steering lines have an o-ringed joint to handle the movement, and if you buy a cheap or cheaply built power steering line, expect that joint to fail almost immediately – that kind of failure happens more than it should these days, and it’s no laughing matter when power steering fails suddenly and the person driving the vehicle is low on muscle power.

When looking for a power steering leak, I like to start by having an assistant turn the wheels while I watch under the hood – if the pressure line is leaking, you’ll find it that way, and it’s wise to wear safety glasses.  Some power steering pressure line fittings are in tight spots where you might get a line wrench on them but have no room to move the wrench, and every technician needs a good set of crow foot line wrenches. Some pressure lines are long and convoluted so as to cool the fluid en route, and some of these convolutes have fins to help with the cooling.

I can’t write about power steering without telling about a power steering pressure line leak on a Lexus SC300 we repaired. When I called the Lexus dealership I rejected the $450 price tag of that power steering line out of hand.  Removing the pressure hose and sending it to the local parts store for re-rubbering turned out to be a disaster because the standard power steering line is 10mm and this Lexus line was 11mm, which bum-fuddled the parts guy, but it wasn’t hard to remedy.  I crocus-clothed the line down to a smooth round 10mm so the ferrules and nuts would work and we fixed that power steering line in short order.

The pulley on just about all power steering pumps requires a special puller, and a good one costs about sixty bucks, but you can buy a decent one for less than $20 on Amazon.com.  Due to variability in the field, some pulleys require more effort than others to remove– it’s a press fit, and they’re all tough, so always put plenty of grease the threads on the pump pulley puller threads or it may weld itself together – I’ve seen it happen more than once, and when that jackscrew stops turning on dry threads you have one piece of metal that used to be two.

Many of today’s pulleys are made of plastic but with metal hubs, and if you buy a cheap aftermarket pulley, recognize the fact that the pulley’s hub might be a bit too small to fit the shaft – this has happened more than a few times and brings the repair to a screeching halt. And on a plastic pulley, putting it in the oven for expansion is a no-go.  The pump shaft itself has threads tapped in the hollow end of it for pulling the pulley back on (the pulley tool has adapters that screw into those threads), but sometimes the threads are filled with rust or stuffed with dirt by dobbers and will need to be chased with an appropriate thread tap. The best pulley tools will have a thrust bearing that makes things go easier, and once again, grease the threads.

Remotely mounted power steering reservoirs are more or less the order of the day, and there is a screen in the bottom of the reservoir that likes to clog, confusing owners who find the reservoir full on vehicles where the steering is whining and hard. This plays out two ways – either the pump will be replaced without the reservoir screen being cleaned, or the pump will be destroyed from fluid starvation because the customer puts off getting repairs for too long. Always check the screen on one of these before replacing the pump, but realize that the pump probably needs to be replaced anyway if the whining has gone on for too long.

As for noise, don’t be fooled by those odd belts that look like sort of like gatorback belts but are shiny on their traction surfaces when they’re new. They can cause a nasty whine that can cause a technician to replace multiple components including the power steering pump. I’ve seen it happen again and again, and while the manufacturer of those belts seems to have stopped making them, you may see one in your service bay. Hear a whine?  Look at the belt.

I don’t like nasty fluid in any system, and this is GM’s way of flushing the system:

With the front end off the ground and properly supported, remove the return line, cap the nipple to prevent leakage, and point the hose at a container, then turn the wheel back and forth (engine off) while adding fluid until the fluid comes out clear. It may take a gallon of fluid, but you’ll get there.

Bleeding the system the right way is similar, but with all the hoses connected. Front end off the ground with the engine off, either spinning the engine (without starting) or not, you turn the wheels back and forth from 12 to 20 times from stop to stop depending on the length of the lines and whatnot. Hydroboost systems take more turns.  Start it, see if it whines, and if it does, repeat the process.

 

A Special Case

 

Another story I have to tell is the one about a 2006 Impala that bounced through a couple of shops (including a local GM dealership) for a whining noise in the power steering.  Neither shop apparently paid any attention to GM TSB (08-02-32-004B), which outlines a vacuum bleeding procedure with a $60 special adapter and a hand vacuum pump.  Well, we fabricated the bleeding tool with a piece of clear hose, a barbed brass connector, and a new rubber oil filler cap. Using the vacuum chamber that comes with hand held vacuum pumps, we installed the home-made rubber bleed cap on the Impala’s reservoir and connected the hose to engine vacuum with the hand vacuum pump’s isolation chamber in line, an arrangement that beats the stew out of pumping vacuum by hand.  After a minute or two of turning the wheels with the engine running, we had taken care of the whining problem without replacing the power steering pump.  R.W.M.

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