Power Steering Lines, Compression Fittings, and Pressure Ratings

[Kurb]

At least one of the power steering lines is leaking on my Trailblazer. Both lines are covered in fluid and rusted pretty bad on the driver's side of the engine compartment, and I have been debating on whether to repair or replace the lines. It looks like it would be much easier and cheaper to repair the lines as discussed in this thread: http://gmtnation.com/forums/topic/1929-power-steering-lines-rotting-away/?p=39502

I have the following questions and would appreciate any other advice:

1. What is the maximum pressure output for the power steering pump?

2. What is the normal pressure rating for brake lines?

3. For the pressure line, I thought about flaring a brake line and using brake fittings, but it looks like people have used compression fittings, which I would definitely prefer. What is the normal pressure ratings for standard compression fittings that you can get at a auto part store?

4. Why are compression fittings not normally used by the auto manufacturers for high pressure systems? I know that they are used in other high pressure applications.

 

[Mooseman]

Compression fittings can be used on the low pressure return line only. I think the pressure line can go up to 700-800 PSI at full lock but also read that some systems can go up to 1000 PSI. I've also found this:

http://bbs.homeshopmachinist.net/threads/42753-OT-brake-line-vs-hydraulic-line?s=db7c44502e72c4c034f0c5c693fe8903&p=575751#post575751

About the most power steering relief valve pressure pressure you will encounter on a heavy vehicle is about 1400-1600 psi.
Doesn't matter if it's a pickup or a Kenworth. The typical car usually has about 2-300 psi less, the main difference is the amount of flow or gpm between small and large vehicle pumps.

Brake systems usually operate at about 800-1000 psi and upwards of 2000 psi under extreme conditions.

So although I believe brake line tubing is up to the task of the pressure, I have my doubts that it can provide the necessary flow, unless of course the tubing is adequately sized.

Not sure if the original power steering pressure line can be double flared. It may be hardened steel or may have become brittle or rusted. Fittings may reduce flow. I'm all for trying to keep old parts going but on this, I think that we don't have much choice but to replace it.

Oddly enough, at both ends of the high pressure line, it's just an o-ring sealing there so I don't know how that works.

 

[ddgm]

Heavy equipment, excavators, front end loaders, etc, use O-rings to seal hydraulic pressure lines. Up to 5000 psi, that I know off and maybe more.

 

[Tiggerr]

Save yourself the headaches and replace them. You'll be way better off. Compression fittings will never hold. You could use a flare nut if you double flare the line. Like you would a brake line. If they're that rotted though it's really not worth it.

 

[Kurb]

Thanks for all the replies and great information. I'm thinking more about replacement now, but I am not sure that I am ready to give up on splicing in tubing. There are definitely sections of the lines that are still in decent shape. When I tear into it, I'll trace the entire lines and really see if it is worth saving any of the lines.

I am thinking that compression fittings might work though, even on the pressure side. It looked like people used compression fittings on the pressure line in the thread that is linked at the beginning of this thread. I know Swagelok makes 3/8 inch compression fittings that have been tested with steel tubing from 3100-6200 psi, depending on the tubing wall thickness. http://www.swagelok.com/downloads/webcatalogs/EN/MS-01-107.pdf

I am thinking that cutting and replacing a section may not only be cheaper but possibly even better than the stock lines. Also, I have heard some people having trouble with hooking the lines to the rack. When I ran into problems with a fitting seized up when replacing a rear AC line, I ended up needing a new rear evaporator, which lead to a new rear HVAC case too. I could have avoided this by just splicing in a line, and I do not want to repeat this.

One concern I have is whether the compression fittings can withstand the vibration and shock loads on top of the high pressure. Is that why they are not used by the auto manufacturers? The compression fittings I used on the transmission cooler line that I replaced are holding up nicely, but I know the transmission fluid pressure is low.

 

[Mooseman]

Like Tiggerr said. If it's the pressure line, replace it. If it blows and lose all your fluid, you will likely damage your pump (been there) and if it's someone that can't drive it without power steering (i.e. the wife) when it happens, it will also cost you a tow and the inconvenience. On the low pressure line, the likelihood that it will blow with compression fittings is low to non-existent unless it rusts through somewhere else. Mine were leaking at the rack, the pump and at rubber to steel crimps so I replaced all of them when I did the timing chain job.

There is no price on peace of mind.

 

[The_Roadie]

If mine were to blow, Mrs. Roadie has arthritic wrists. It's doubtful she could recover from a steering seizure, depending on what conditions she's in for traffic and terrain. But she would almost never be driving mine unless I was incapacitated and she was getting us back to pavement. Her car is a lot smaller and can be handled if the steering goes out.

 

[Kurb]

I went through a quart of power steering fluid in about 50 miles, so I couldn't ignore the leak any more. It turned out to be the return line. It was leaking in front of the strut tower on the driver's side where both lines are bolted to the frame. As a short term fix, I just cut the metal line in front of the strut tower and ran a hose to the cooler. I used 400 psi rated hose with a fuel line hose clamp (regular clamp probably would have been fine) on the cut line end and reused the existing hose clamp on the cooler. If I planned it better, I would have cut the hose that goes to the rack and used a barbed union to attach a new hose from there to the cooler to eliminate all of the metal line.

I will heed the advice, though, and replace both lines with the correct parts when the weather is better and I have more time. Both lines are rusted in several locations, and the high pressure line looks pretty bad at the bracket where the low pressure line leaked, although it is not nearly as bad as the low pressure line was.

 

[danj]

The pump in your truck is capable of putting out around 1300psi.

 

[joe mama]

Great discussion. Mine is leaking, not sure from which line, but it's where the lines are next to each other on top of the front wheel well. I refilled the reservoir, and have driven nearly 800 miles since then, so I am thinking it's the return line because the leak is so slow. My thinking is that if it were the high pressure line, it wouldn't last 800 miles after filling the reservoir.

 

[danj]

If the leak is on the pressure hose by the crimped section it will start really slow like you're seeing. If you let it go it will get worse with time. How long have you had the leak?

 

[smokey262]

To accurately select any tube fitting you need to know the OD, ID, max pressure, and tube material. The only data missing from this thread so far is the ID, or we could calculate it if we knew the wall thickness.

I have used Swagelok products for years in high pressure industrial hydraulic applications to 3000 PSI, though not on a car yet. I would not hesitate to use them in this application as long as I selected the proper components

 

[joe mama]

Leak has been there since November or December, although I've only driven about 2000 miles since then. If I get some time this weekend, I'll try to inspect it closer and find out exactly where the leak is. Hopefully it's the return side.

The rubber bracket on top of the strut tower is wet on the front end, and there is a thin layer of fluid underneath it. After parking for a day or 2, there will be some spots in that area

 

[danj]

If the leak is slow like that I would bet it's the return line. If it were the pressure line the leak would almost come to a stop once it's not under pressure.

 

[joe mama]

OK, it's now visually identified: Pinhole leak on the return side (the outboard line, compared to the pressure side).

I finally had an weekend afternoon with minimal kids' lacrosse/volleyball/birthday parties etc., so I had some time to take the holder off. It's a pinhole leak that was underneath the evil 4 inch-long rubber line-holder. Thank God it wasn't on the pressure side! This should be a reasonably easy fix now.

I'm open to suggestions on the best course of action, and just need something that will last for a few months, as the family is moving to Germany in July thanks to Uncle Sam's Navy.

 

[mubai]

I replaced mine recently. Same exact issue. Wasn't too bad at all, even in a cramped garage.

https://gmtnation.com/forums/thread...ithout-power-steering-fluid.12848/post-410893

 

[Mooseman]

Compression fittings and a piece of brake line of the same size works well as per the pic in this post:
https://gmtnation.com/forums/thread...ithout-power-steering-fluid.12848/post-409621

 

[joe mama]

I went the easy route, and put on a "power steering return hose" that I bought from Advance Auto last night. Cut it to size to replace the steel line that I cut out, and double hose clamped each end. Leak is stopped, and drove the TB to work this morning.

The high pressure side isn't leaking, but has a bit of rust on it, so I'll get some rustoleum, put it on there, and monitor it.

Any issues with the layer of fluid that is coating everything under the engine? I intend to wash it off, but will it damage anything before I can get to it?

 

[Mooseman]

Nope. It's not like brake fluid. Just an oil based fluid.

 

[Tiggerr]

I went the easy route, and put on a "power steering return hose" that I bought from Advance Auto last night. Cut it to size to replace the steel line that I cut out, and double hose clamped each end. Leak is stopped, and drove the TB to work this morning.

The high pressure side isn't leaking, but has a bit of rust on it, so I'll get some rustoleum, put it on there, and monitor it.

Any issues with the layer of fluid that is coating everything under the engine? I intend to wash it off, but will it damage anything before I can get to it?

Free rustproofing! lol!

 

[Kurb]

Although I bought the lines a while ago, my temporary fix was working so well that this job fell off the radar. Now I've got another leak, so I plan to tackle it this weekend.

Should I also replace the power steering pump? The pump runs quiet (until the fluid gets too low) and seems okay. However, I had a coworker who replaced the lines, and one of the new lines leaked shortly afterward. He replaced the pump and the line and did not have any more problems. I am wondering if the pressure relief portion of the flow control valve goes bad and that could cause the pressure to go too high. This may also help explain how my recent leak started out really bad a couple days ago (fluid everywhere on the driver's side of the engine bay and a puddle on the driveway), but I did not have to add any fluid the last two times I drove it.

 

[NJTB]

I just did this a few months ago. The lines were leaking in the same spot, and I was going to splice and double flare them. One of the members on this list suggested Swagelock fittings, and they worked like a charm.
Swagelocks work similar to a compression fitting (there's no ferrule), but are rated to the burst pressure of the line.
I checked the line to make sure there were no other bad spots (there weren't), got some brake line from Autozone, cut out the bad parts and cut and bent the line to fit.
So far (about 5 months), it's worked great with no leaks.
If you're interested:
Swagelock
R.S. Crum & company
1181 Globe Ave.
Mountainside, NJ 07092
908-232-4444

There may be a dealer closer to you, Google it.

 

[danj]

Although I bought the lines a while ago, my temporary fix was working so well that this job fell off the radar. Now I've got another leak, so I plan to tackle it this weekend.

Should I also replace the power steering pump? The pump runs quiet (until the fluid gets too low) and seems okay. However, I had a coworker who replaced the lines, and one of the new lines leaked shortly afterward. He replaced the pump and the line and did not have any more problems. I am wondering if the pressure relief portion of the flow control valve goes bad and that could cause the pressure to go too high. This may also help explain how my recent leak started out really bad a couple days ago (fluid everywhere on the driver's side of the engine bay and a puddle on the driveway), but I did not have to add any fluid the last two times I drove it.

If the flow control valve goes bad the pump will just not produce pressure. There is no issue of it creating too much pressure unless the system is restricted causing it to operate at full pressure (around 1200psi). If your pump is working, and isn't noisy then there is no need to replace it.

 

[danj]

Another issue to watch for after replacing the line is that you have to bleed the system of air before starting the truck. If you don't air can pass by the flow control valve, and cause it to get hung up. This will cause the truck to lose assist. To bleed the system correctly you want to make sure you have the system all hooked up just as you would want it to be while your driving it down the road. Don't crack a line to bleed the system. You'll only introduce more air that way. For a bleeding procedure I would recommend;

1.Pull the fuse for your fuel pump.
2.Secure the front end off of the ground, so there is no resistance.
3.Using the starter crank the truck over. While its cranking turn your steering wheel from the center position back, and forth a couple inches at a time. Each time you turn add a couple of inches to your turn.
4.Since you don't want to burn out your starter, give it a break after every 5-10 seconds of cranking. When you give it a break get out and check the fluid reservoir. If you see any foaming, or bubbling just walk away for a bit and let the fluid settle.
5. Once the fluid is clear start the process over again. Once your able to go from lock to lock without seeing any foam/ bubbles in the reservoir your system should be completely bled of air. Put the fuel pump fuse back in, and start it.

Hope this helps.

 

[Mooseman]

From what I read (in the manual IIRC) you would do the same thing but no need to spin the starter. And then do it again with the engine running at idle to be sure all the air got out.

 

[danj]

The problem with not spinning the starter is that the pump won't generate any pressure. The plates inside of the pump are centrifugal. Without any pressure the air can get trapped in the many places in the system.

The reason you don't want to start it right away is with the engine running the pump spins at a fast enough rpm that the fluid exchange in the reservoir is almost immediate. If the air comes up through the return line while the vehicle is running the air will get pulled through the pump right away, and there is a very good chance that it will hang up the valve. By just using the starter the pump builds pressure, but the fluid exchange rate drops significantly.

This is a very common issue that people run into. I diagnose a stuck check valve do to incorrect bleeding procedures on what I would estimate to be around 85% of the technical service calls I get every day.

 

[Kurb]

If the flow control valve goes bad the pump will just not produce pressure. There is no issue of it creating too much pressure unless the system is restricted causing it to operate at full pressure (around 1200psi). If your pump is working, and isn't noisy then there is no need to replace it.

Thanks. I didn't replace the pump, just the three lines, but doesn't the flow control valve have a pressure relief valve that allows flow to bypass to the suction side of the pump if the pressure gets too high? The following website says that the flow control valve prevents excessive pressure and has a diagram showing the relief valve: http://www.cdxetextbook.com/steersusp/steer/boxesColumns/flowcontrolvalve.html
After replacing the lines, now the cooler is leaking near the return hose connection, so I bypassed it.

EDIT:
After thinking about this a little more, I see your point. Per the above website (assuming the Trailblazer is set up this way), the relief valve is only supposed to open when the rack is at the stops and flow is blocked. This would not cause excessive pressure in the return line, which is where my leaks started, probably since this line had a thinner wall, and it took a little less time for the rust to eat through it. It certainly would not have caused the cooler to leak, since the leak is on the pump suction side of the cooler.

 

[NJTB]

D

Thanks. I didn't replace the pump, just the three lines, but doesn't the flow control valve have a pressure relief valve that allows flow to bypass to the suction side of the pump if the pressure gets too high? The following website says that the flow control valve prevents excessive pressure and has a diagram showing the relief valve: http://www.cdxetextbook.com/steersusp/steer/boxesColumns/flowcontrolvalve.html
After replacing the lines, now the cooler is leaking near the return hose connection, so I bypassed it.

Did you splice the lines in or replace the whole set?

 

[Kurb]

I ended up replacing the lines with lines from Advance Auto per earlier recommendations that splicing would not eliminate all the leaks. The lines did have several areas of rust in addition to the leaks. I originally had spliced the portion of the return line from the strut tower to the cooler with a hose and hose clamps, but then the pressure line started leaking, and I think the return line sprung a second leak as well.

 

[Kurb]

I did want to mention that this turned out to be much more difficult than I expected; of course, some of the pain was self-inflicted. Here are some tips:

1. You can get the lines on and off by removing the battery, battery tray (remove horn to get to front bolts), and the bolts holding the fuse box, and disconnecting the two ground wires from the body. I also disconnected the air conditioning line mounts and several clips holding the wiring harnesses.

2. Removing the old cup seals was a real pain. I tried several different ways to get to them before I found a way that worked. I ended up buying a seal puller and working from underneath. There is an opening behind the rack where I reached in with the puller. I was able to barely get my left fingers to the seals to guide the puller into the openings and use my right hand to push the puller forward to pry the seals out. It was completely by feel. I then used a flashlight and a mirror to verify the seals were out since they disappeared (until I later found them while looking for other dropped things).

3. In my case, I am pretty sure I would have saved time if I pulled the axle. I didn't do this since others that posted did not seem to have a problem with the axle in. It is definitely not necessary, but I think it would have made it easier to get to the seals to pull them and to reinstall the lines, and since I ran into problems, it would have saved me time in the long run.

4. You can access the lines at the rack connection from the top of the engine. I did not realize this at first, but after having issues putting the new lines in (having the cup seal pop out while trying to push the lines in, dropping the seal and losing it this time so that I had to buy a new one from the dealer, dropping the 8 mm retainer bolt and spending an hour looking for it, etc.), I tried installing the the cup seal and new lines from the top, and it was much easier. I just removed the brake booster vacuum line to make more room for my arm, and then I layed on top of the engine and reached in with my left hand.

5. Put shop towels and/or cardboard below the the rack connection before removing and installing the lines and seals. Before I did this, I dropped things (bolt, seal, and tools), and they would vanish. Although this was meant to make it easier to finds things when I dropped them, this seemed to cure me from dropping things.

6. Working from the top of the engine, it is not that difficult to push the lines through the cup seals. I was nervous that this might be difficult and I might damage the seals doing it, so I tried to buy lines with the o-rings instead of cup seals. When I went to install the aftermarket lines from Advance Auto, only the pressure line had an o-ring. Even though the return line was supposed to have an o-ring according to the part description and the instructions that came with the line, it came with a cup seal instead. I returned it, but none of my local part stores had the return line with an o-ring in stock, so I ended up trying the cup seal. I think it may have helped since the line stuck in the seal after I got it started by hand from above. This allowed me to go in through the wheel well to pry it in farther with a screwdriver, and the lines stayed in place when I worked from the top to get the bolt started. I think the cup seal helped keep the lines from falling out. I then used a ratchet and extensions on top of the axle as others have recommended to install the 8 mm bolt.

7. This is obvious, but pay attention to the line routing before you remove the lines. Maybe take pictures. I initially routed the pressure and return hoses that go to the rack between a wiring harness and the back of the strut tower. After connecting the lines to the rack, I realized that they needed to go over the wiring harness to avoid rubbing and to allow the lines to fit properly.

8. I could not get any of my tools to fit on the front mounting bracket bolt that mounts the pressure and return lines to the frame on the driver side, near the front of the engine bay. GM decided it was a good idea to put the bolt between the lines to block access for a wrench, and then align the center of the bolt with the body so that even my 1/4" drive ratchet would not fit. I put a small 10 mm socket on the bolt and used vice grips to turn it. I wrapped electrical tape around the socket to keep it from getting scratched up by the vice grips.

9. I removed the mounting bolt near the crankshaft pulley with a 10 mm wrench from the top, squeezing my hand in the small space and turning the fan while I turned the wrench. This would have been less painful if I had removed the fan, but it would have taken longer. I installed the bolt the same way but from underneath with the truck on jackstands, and while this took a little longer than from above since I could not see what I was doing, it hurt less.

10. Be careful with the stud for the battery mount. I had the battery out a few times before with no issues, but for some reason, this time the stud decided it was going to unclip itself and fall into the wheel well.

11. Removing the air box and windshield washer fluid reservoir is easy and makes it really easy to get to the power steel pump connections.