Power Steering Flushing & Bleeding Procedures?

Is there a problem you're trying to solve? Power steering systems typically get ignored because they don't require regular maintenance. Most commonly we do need to bleed the system after repairing a leak. In most cases that involves turning the steering wheel to full-left, then to full-right a couple of times with the engine running. The reservoir must be kept filled to prevent the pump from drawing in more air. In a few models, particularly with rack and pinion steering gears, it can be helpful to drive one front tire up onto a curb or on anything that will make one side higher than the other. If you don't do that, what little air might be trapped in the gear will work its way out over time. Recheck the level in the reservoir after a day or two.

To flush the system, probably the best way to do that is to remove the low-pressure return hose from the reservoir and run it into a container. That way fluid will only flow when the steering wheel is turned, giving you control to prevent running the pump empty. Keep adding new fluid so the pump doesn't draw in air.

To identify the hoses at the pump and reservoir, the high-pressure hose will have a crimped metal sleeve over the end of the rubber hose where a metal tube ends with a soft metal nut. The low-pressure return hose is usually just a rubber hose slid over a tube on the reservoir, and held on with a simple spring-type hose clamp.

There's some special considerations for Ford vehicles. First, it is extremely important to not allow any air to enter the system. This can't be avoided when replacing hoses or steering gears, so there are a number of special tools available to reduce the frustration of bleeding. One of the more popular ones is a funnel designed to snap onto the reservoir. That funnel can be kept over-full to allow air bubbles to burp out while preventing air from entering. The air pockets floating out tend to splash power steering fluid out too. That's what makes it next to impossible to keep the reservoir full. The splashed fluid stays in the funnel, then runs back into the reservoir instead of all over the engine and onto the floor. There are also vacuum pump tools designed to put the power steering fluid under a vacuum to cause trapped air to expand and come out easier, but I haven't had much luck with those.

The problem with trying to burp the system like we do with other brands, by just putting the cap on the reservoir and running the steering wheel back and forth, is so much air burps out of the steering gear that it lowers the fluid level in the reservoir until the pump just draws the air back in again. Even with the funnel, it's not unheard of for it to take an hour or two to get most of the air out.

Some people say they've had success bleeding out most of the air on Fords by raising the front tires off the ground, then turning the steering wheel back and forth with the engine off. This way the fluid is not under pressure. That keeps the air in the system from being compressed. You still won't get all of the air out, but it may be enough that you only need to top off a little a day or two later.

There's one more note that to my knowledge, only pertains to Ford models. If you do need to remove either hose from the steering gear, most of them are held on with a soft metal nut, but that doesn't do the sealing. There's a rubber O-ring on the end of the metal pipe that does the sealing. When the nut is tight, that pipe can still swivel and feel loose. That is normal and acceptable. The O-ring is a common source of leakage so new hoses and new steering gears come with new O-rings. What causes many people to be needlessly concerned is over time, the old pipe corroded to the nut and no longer swivels freely. When reinstalled, the hose does swivel, making it appear to be not fully tightened.

The air should have worked its way out by now. As for the leak leading to pump damage, I'm skeptical of that. The noise was there from the start, so I'd be more suspicious of the pump itself. There's two things that can make them noisy. One cause is from the vanes on the pump's rotor. I don't know how that manifests itself but I have solved a few by replacing the new pump under warranty.

The other cause is related to the low fluid level. That is the pressure check valve in the pump's outlet port. I don't know how they do what they do, but essentially, they reduce fluid pressure when no fluid is flowing, and increase pressure when you turn the steering wheel. It's a spring-loaded valve, and that's what buzzes loudly when there's air in the system.

The fact you observed there's no air in the fluid suggests air isn't the problem. When air is trapped after this long, instead of being dissolved in the fluid, it pools at one end of the steering gear's power piston. It some point it manages to find its way out. The common complaint is that happens when the engine is stopped, then the pressure goes away, the air quickly expands, and a bunch of fluid burps out of the reservoir. When that puddle on the ground isn't noticed, the air that's now in the reservoir gets drawn back into the system the next time the engine is restarted. Sometimes that "blurp" of fluid occurs hours or days later, but in the meantime, the system is usually quiet.

If there's tiny air bubbles in the fluid, those will gradually float out of the fluid in the reservoir when the engine is off. Until that happens, that air can be compressed. It makes the pressure valve vibrate and make the buzzing noise, but that goes down over time.

The fluid level in the reservoir shouldn't change much between engine off and engine running unless there's dissolved air in that can be compressed. As long as there's just enough fluid so you can see it near the bottom of the reservoir, don't add any to top it off at this time. Watch if the level drops over the next few days or weeks. If it does, and you don't see any leaks, the level is going down due to dissolved air working its way out. Add just enough fluid to prevent air from entering the pump. If the level doesn't go down, I'd pursue replacing the pump. I've been involved with a few that developed worn vanes, but those fail to build pressure, and they're uncommonly quiet.

Another way that has worked at times to find if the pump is just noisy is to listen right next to the outlet hose on the large nut, with a stethoscope, engine running. Have a helper turn the steering wheel back and forth slowly. If the noise gets louder when the steering wheel is turned, that suggests it's coming from two different causes. One is the normal pump noise and the other is the pressure valve. To say that a different way, the normal valve noise isn't there when the steering wheel is not moving, leaving the pump itself as the source of the noise.

I'll be back tomorrow to see what you find with these observations.

I don't think trapped air is the problem. You're well past that. The idea with the vacuum pump is there's a large pocket of air pooled in the steering gear that is trapped in a high spot and can't work its way out. The engine must be off so the power steering fluid is not being put under pressure. That alone allows the compressed air to expand. The addition of vacuum makes that pocket of air expand more until hopefully, some of it can sneak out, then flow up to the reservoir when the engine is restarted.

The reason I don't think you have any trapped air left is when the reservoir is full, you start the engine, then the pressurized fluid forces that air to compress, making it easier to hide in some obscure place. That might result in a steering wheel shudder, but often there's no other symptom until you stop the engine, then the air can expand again. That expansion pushes fluid up into the reservoir, often with plenty of force to blow some out and all over the engine. That's part of the frustration. The steering can seem fine, but it keeps spitting out fluid. You're not seeing that fluid dumping out. The tiny bubbles you did see sound to me to be insignificant.

While not conclusive, something you might consider is to remove the belt, then spin the pulley by hand to feel for roughness. It should be smooth, quiet, and turn freely. If you feel roughness, suspect the shaft rides on ball bearings and the race has worn spots that were overlooked by the rebuilder.

Another trick, when you have a spring-loaded tensioner pulley, is to carefully release some of the tension while the engine is running. Be careful of the belt, and neck ties and loose clothing! Only do this when you can release the tension with a long ratchet handle that keeps your hands up high, away from the pulleys. You can still have noisy bearings even when the shaft seems smooth and quiet. That noise can become more pronounced when sideways pressure is put on the shaft by the tension on the belt. If releasing tension reduces the noise, suspect the bearings.

Something much less common to look for is a result of "memory steer". That is when you turn the steering wheel one way while driving, and it stays there until you pull it back to center by hand. That was real common many years ago on Ford trucks with kingpins. Today the biggest cause is tight universal joints in the steering shaft, under the dash. While standing still, that could put pressure on the spool valve in the steering gear just like if you were to put a finger's worth of pressure on the steering wheel. That can be just enough force to make the pressure valve in the pump vibrate and make noise. The clue to this would be the noise is reduced when you try to turn the steering wheel with just a little pressure one way or the other. Normally with memory steer, noise never gets discussed because the binding when turning the steering wheel is more serious. With no binding, when you can make the noise change by doing this, a better suspect is a spool valve coming apart in a rack and pinion assembly. I've never seen this in an older, heavy, steering gear box. I have been involved with at least two rack and pinion assemblies where the steering wheel would keep on turning by itself after the driver turned it a little, then let go. With this type of problem, there's usually other additional symptoms related to the feel, or binding or clunking, of the steering wheel.

From everything you've said so far, my suspicion is the hydraulic system is bled properly and it's just the pump is noisy. Nothing else suggests there's still air in the system.

I should mention too, there's really no place air can be sucked in other than running the reservoir low. There's three rubber lip seals in a rack and pinion steering gear, two in a gear box, and just one on the shaft of the pump. They're designed to hold pressure in. More pressure pushes the lip against the metal shaft harder to form a tighter seal. Too much vacuum on the system can pull air past those seals, so I wouldn't rely on that to say there's no leaks. We do use vacuum testing with air conditioning systems, but compressors use a different type of seal that will seal both ways.

My only experience, while quite limited, with replacement pumps, is from working at a very nice Chrysler dealership in the '90s. If the pump was on a vehicle under warranty, you got a brand new one to replace it. That was true of any part because their policy was if any part was replaced under warranty, it had to return the vehicle to like-new condition. That was the only way to get a brand new pump or a brand new steering gear. For vehicles out of warranty, the people in the parts department were able to order those new parts if the car owner insisted, but that never happened because of the very high cost of rebuildable parts. For example, back then, a rebuilt rack and pinion steering gear from Chrysler cost around $100.00 for a rebuilt unit, and well over $500.00 for a new one. The same applies to brake master cylinders, alternators, and things like that.

Even when you order a rebuilt assembly through the dealer, it is usually rebuilt by a contract shop, sometimes the same supplier that originally made them for the manufacturer. Prices vary a lot between rebuilt parts depending on how the job is done. Parts rebuilt for the car manufacturer and sold through their dealers' parts department will usually be more expensive because they typically inspect, then reuse the housing and a few major parts, and replace everything else, even when some of those smaller parts are still okay. This is the closest to a part that's identical to the brand new one.

Some of the low-end, or "economy" rebuilders only repair or replace what is necessary to make the assembly work. This would be little better than finding a good, used assembly in a salvage yard. These are less common than you'd think because there's little incentive to going through all the work of taking things apart, cleaning them up, then putting them back together with a good chance they're going to fail again.

In between are the rebuilders that disassemble and inspect the old unit, replace broken or worn parts, then replace all the parts that have a history of causing problems. They also incorporate any updates or improved parts that have been developed. Automatic transmissions are good examples of this. Often you will get these improved versions right from the car manufacturer even though it was the original supplier or an aftermarket supplier that researched and developed the better parts to address a known issue. In these cases the rebuilt assembly can be superior to the original assembly.

New assemblies come down an assembly line with each person doing one specialized task, and doing it well, with exactly the tools and jigs required. Mistakes and failures are almost non-existent. Those jigs and tools can be very expensive and custom made, but are a good value since they're used over and over on thousands of assemblies. Rebuilt parts are typically disassembled with each part being thrown in a bin of identical parts. After cleaning and inspection, one person draws a used part out of each bin and hand assembles them into the complete assembly. He doesn't concentrate on just one task over and over, so it's much easier to make a mistake. He may not have the correct installation tool that prevents a rubber seal from being nicked, for example. Those expensive custom tools and jigs aren't available because they're too expensive to justify buying them for such a limited use. I can think of a dozen stupid little mistakes you or I would make that might not cause a problem except when just the right set of conditions occurs. In particular, I'm thinking of things like a metal chip getting embedded and overlooked in the bottom of a threaded hole. In a hundred cases, the bolt going into that hole might be short enough to not come close to that metal chip 99 times. That's little consolation to the one person who gets the one where that chip makes the bolt bottom out and appear to be tightened to specs before it reaches the expected clamping force, and results in a leak.

The bottom line is the low-end rebuilt parts are usually at least as good as the original ones were. That's not to say the car manufacturers use the cheapest parts they can find. Rather, they require suppliers to make parts that meet a specific set of specifications, then, for the aftermarket replacement suppliers, none are going to intentionally build inferior parts. It doesn't cost them any more to design and build something better than the original version. If they can advertise an advantage or an improvement with their part, or if they can develop a reputation for building quality parts, they will want to do that.

With that said, Cardone and AC Delco are two well-known rebuilders I've heard of for larger assemblies like power steering pumps. Moog is probably the top company for researching and developing steering and suspension parts far superior to original equipment designs. The best examples of these are replacements for Ford tie rod ends with a history of huge failure rates. Doorman does a great job of providing small mechanical parts not available anywhere else. Knobs, handles, parts for power window mechanisms, and things like that are their specialty. Standard Motor Products specializes in reverse engineering electrical parts with high failure rates, then developing solutions that address those shortcomings. You'll commonly find ignition modules, voltage regulators, power lock and power window switches and motors, and things like that.

Fortunately, it's much more common to find a parts supplier company with a reputation for making better parts than the originals than it is to find one with a bad reputation. In fact, the only company that comes to mind right now is one that remanufactured tv picture tubes in the 1970s. Those looked weak as soon as we installed them. Every mechanic will share stories of a company they've had bad luck with. My mind is drifting now toward those that rebuild half-shafts. Taking them apart and putting them back together requires very little training or special talent, so one form of wear very commonly gets overlooked. In cases like this, just as important as the quality of the job is the warranty and the rebuilder's reputation for solving these problems. A common problem half shafts can cause is a harsh steering wheel wobble at lower speeds. When those shafts are purchased from places like O'Reilleys, Auto Zone, Advance, and Napa, I've never heard of anyone being refused a replacement shaft under warranty. Some even reimburse mechanics when they have to do the job a second time.

I don't know if you can find the answer you're looking for in that story. One thing that hasn't been mentioned yet is the pump for your truck does not have a reputation for failing, so you might consider getting a good used one from a salvage yard. With the mileage on your truck, a used pump is likely to have less wear than your original pump. If you prefer to go with a rebuilt pump, I use the Rock Auto web site for reference quite a bit. If you click on the blue "info" button, it will take you to a page where each supplier gets to brag about their products and tell you why they're a good value. You can still get one with a problem from the best supplier, and you could get a good unit from the worst supplier. That's why they all specify some type of warranty.

Typically not. Some will say if you see metal particles in the fluid from the part that came apart or failed, you want to flush the fluid to get that out, but realistically, there's always going to be a little debris circulating, and if that was going to do damage to the steering gear, it has already been done. That means there's nothing to gain by flushing the fluid now.

If it will help you sleep better at night, you can disconnect the pressure hose from the pump first, then turn the steering wheel from side to side a little with the engine off. That will push fluid out of the rack assembly and back up into the reservoir. (It might overflow). You'll get more of the old stuff out, but remember, that's going to introduce more air that has to flow through the rack to get back to the reservoir. You already experienced the characteristically difficult bleeding problem. My preference would be to keep the hoses full of old fluid so there's less air to get out.

In over 25 years as a steering and alignment specialist, I suspect I've replaced less than five power steering pumps. The story is different for rack and pinion assemblies. I'd guess I've done over 50 of them. When the control valves come apart, they can chew into the housing creating metal chips. Even those don't seem to cause damage to the pumps. Normal procedure was to just bolt on the new part, fill it, align it, and buzz off into the sunset. Other specialists may have different experiences, but for my tastes, I suspect you're over-thinking this. What might make more sense would be to replace the pump, get the air bled out so the system is working quietly, then use a turkey baster to suck fluid out of the reservoir with the engine off, and refill it before starting the engine. Check the old fluid for metal chips. I don't think you're going to see any, but if you do and want to go further, again, once the air has been bled out, I'd remove the fluid return hose at the reservoir and add an extension hose so you can run it into a drain pan or can. You won't be able to catch the fluid dripping out of the reservoir's tube, so cap that off. Fill the reservoir, start the engine, then have a helper turn the steering wheel slowly from lock to lock. The entire rack and pinion assembly holds less than a quart of fluid. As you run it from full-left to full-right, the power piston will push that fluid out through the return hose, and draw in fresh fluid on the other side of that piston. Keep filling the reservoir so the pump can't suck in air. You could go through as much as two quarts of new fluid. The goal is any metal chips in the rack will wash out with the fluid. That fluid only flows when the power piston is moving, meaning you're turning the steering wheel.

To block the tube on the reservoir, if you're lucky enough to have an assortment of plastic caps that come on hydraulic parts, use one of those. Otherwise, I use a short piece of hose the correct size, on the tube, then I stick the smooth end of a drill bit into that hose. If you have that cap or hose ready to go as soon as you pull the hose off, you won't lose much fluid or make too much of a mess.

These metal chips are much more serious in automatic transmissions and their coolers, so special pumps and chemicals are made to flush those when replacing the transmissions. They use a number of a different type of rubber lip seals that can be cut by those chips. Power steering systems, while still a hydraulic system, use different types of seals less prone to damage. That's why regular fluid changes are not necessary, and those systems don't have regular filters, like oil and gas filters. There is an inline filter often available that at times, has been supplied with a rebuilt steering gear. The rebuilder requires one to be installed to maintain the warranty on the new gear. Those filters get stuffed into the return hose. I've never heard of one of those becoming plugged, but if one did, I suspect it would blow the return hose off the steering gear end of the hose. The pressure side can reach over 1,500 psi. The return hose has 0 psi in it, but if blocked by a plugged filter, that 1,500 psi would transfer through the steering gear and appear on the return hose. That one is just held on with simple, weak, spring-style hose clamps, so they'll push off rather easily. Again, I've never heard of that because those filters are long enough that to have enough metal chips to plug them, something else would have to experience a catastrophic failure first.

Do you have any good news to update? Is the system working properly now?

Dandy news. Happy to hear you solved this. Please come back to see us again.