Some folks will drive vehicles for many a mile with inoperative power steering or brakes. 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 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.
While the long time norm for power steering was to have an integral reservoir right on the pump, space considerations have driven engineers on some platforms to mount the reservoir remotely with a very compact pump sequestered somewhere below it – the fluid is fed through a screen and travels to the pump through a large hose. This makes the reservoir easy to access, too.
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 1970s Mustang with power steering trouble. 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.
Electric power steering comes in many forms – here are two. The top photo is the electric steering unit from a hybrid vehicle. The bottom photo was taken under the dash of a 2005 Chevy Cobalt, which is similar in form to the Toyota Prius – all you see under the hood on a Cobalt is what looks like a manual steering rack.
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. 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.
Two things here – first, the curvy routing of many power steering lines that seem longer than necessary is specifically engineered to cool the fluid, which is heated as it is pressurized by the pump. Secondly, these Teflon® sealing rings on Ford power steering fittings are slightly a pain to install if you don’t have the cone-shaped tool to stretch them over the threads, but it can be done. And a new one is just about always needed after the line has been disconnected.
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. 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, and the opposite end of each tie rod is 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.
The new power steering pump in this picture was replaced because the owner drove it for more than a year with the remotely mounted reservoir screen stopped up. Even after the screen was cleaned, there was no power assist. This pulley is the original one, and the puller bolt is threaded into the pump shaft in preparation – but be careful when you’re replacing one of these pulleys with an aftermarket one – some of the Chinese ones are a bit too tight and won’t go on. And don’t put the pulley on backwards.
What to Do
Power Steering pumps produce between 1,200 and 2,000 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.
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Oil-leaking steering rack boots are a dead giveaway. Nothing but air is supposed to be inside this boot. This steering rack needed replacing or re-sealing – we replaced the rack with a reman unit.
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 might 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.
Dye is obviously one of the best ways to find a power steering leak – this 2007 Chevy pickup was leaking at the return line seal of all places, and right after the rack was replaced… Parts stores can’t get these line seals without ordering the whole seal kit.
Power steering lines have distinctly bent metal tubes where they connect to the steering pump and the gear and because 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.
One important point to remember when replacing a steering rack is to lock the steering wheel in the center and make sure it stays there, else you may destroy the airbag clock spring – one of my students ruined the one on his Honda Civic that way – that clock spring was nearly $400.
The pulley on just about all power steering pumps requires a special puller, and a good one costs about $60, 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 on the threads on the pump pulley puller threads or it might 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.
Make sure to generously grease the threads on your puller – I’ve seen more than one of these pullers weld itself together to the point of ruin when the pulley was being difficult – and some power steering pump pulleys are extremely tough to remove. Note also the large diameter of the pulley – this pump works hard.
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 might see one in your service bay. Hear a whine? Look at the belt.
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