I have 2004 T4R sport V8 4WD 4DR installed a new lower return line (amazon: A-Premium Power Steering Pressure Hose Line Assembly Compatible with Toyota 4Runner & Lexus GX470, 2003-2009, V8 4.7L, Replace for 3401235, 4441335010) and new air vacuum control (ebay: OEM# 17630-16040 FOR TOYOTA LEXUX VALVE ASSY, POWER STEERING AIR VACUUM CONTROL)
My only issue now is I can't get the driver side connection to quit leaking. Any suggestions?
Thanks,
Dena

Isn't the PS return line just hose clamp? Is it a hose clamp you're having a problem with, or is it a hose with threaded fitting ?

hose with threaded fitting

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If its truly the return line its not under pressure. Reinstall the old part and cut off the leaking section. Hose clamp a hose to the stub and rout it back to the res. But if its the pressure hose from pump tighten it a little more or return it.

Where exactly is it leaking?

Check rockauto. You might have the wrong part for the return line. They show two parts; hose kit and rack connector.

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Your pic shows a pressure line. The return line from rack to reservoir will have a threaded fitting to the rack ( driver side ) and hose clamp at the reservoir ( passenger side). If leak is at rack side, you may have cross threaded when installing fitting to rack ( apparently quite easy to do ). Hope its not the case here. Like others had mentioned the return line sees very little pressure, just head ( height difference between rack/reservoir ) and some line friction forces from rack to reservoir.

It’s the pressure hose then. The one with the threaded fitting on the drivers side. I can’t get it to thread at all now. I had it threaded, it leaked pretty bad so I thought I hadn’t done it right. Took it off the car to start all over again. Now I can’t get it to thread at all… so frustrating!! It’s at kind of a weird angle. I’m not sure what I’m doing wrong.

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You've probably got the thread in the steering rack boogered just a little and you're going to have to be lined up just right with right amount of pressure to get it started, it may take 20-30 minutes or more to get it going unless it's really damaged. Try turning the fitting in the loosening direction with a little pressure on it until you feel it "click, then try going tightening direction with a little pressure on it. I know what you're going through and it takes time and just the right combination.
Look closely at the threads on the fitting on the hose make sure they are not damaged on the very end, if they are take a fine file and try and smooth them out.

If following @rdruss instructions were a no go, you may want to try this. Instead of trying to thread the new hose’s fitting into the rack, cut off the fitting from the old hose and try again with @rdruss ’s procedure. Lining up the old fitting w/o the hose is much easier to get the two components to line up dead straight.
If all the above fail, you’ll need to beg, borrow or rent a tap & die set to chase the threads of the rack and the new fitting. Hopefully there is space to accommodate the tap when fixing the threads in the rack. Also need a telescopic pen magnet, or similar to clean out any metal debris from rack. It’s a delicate operation, so lots of patience required and do not rush.
Lots of luck to you and hope that all ends well.
Worse case scenario will be a rack & pinion removal to fix the threads in the rack.

Good replies above. One thing to note whenever doing these types of connections, try turning the steel line a bit to see if it's loose after installing. When tight it will not move at all. If it moves it will leak.

Also, if the threads look messed up on the new line you may just want to get another and try again. You should never put a wrench on it until you can spin it on by hand at least a full turn. Hopefully the threads on the line are softer than the rack ones.