It makes sense because I changed the pump and it was fine for a few days also.

 

Here is the spool or rotory valve; I think if it is not working right it will direct the oil to the wrong places at the wrong time.

HowStuffWorks "How Car Steering Works"

And from FixYa; Usually you can check this kind of problem by jacking up both front wheels and starting the engine. if you begin to turn the wheel, if the valve is bad, the wheel will continue to turn by itself.
If you verify the problem, steering boxes are generally available from scrapyards at far less cost than reman or new, and not nearly the time and effort of a rebuild yourself. If you do the job, you will need a pitman arm puller, and flair nut wrenches for lines.

Also from FixYa; if the spool valve leaks it can apply a slight pressure to turn in the direction of the leak, this valve is what directs fluid pressure in the directive you want to turn to provide power assist, another issue is

From E-How; Hydraulic Spool Valve Basics
A hydraulic spool valve is a switching device used to control hydraulic devices. Spool valves are used in everything from automotive power-steering systems to cranes. A spool valve can turn the flow of hydraulic fluid from a hydraulic pump to an actuator on and off by blocking off the route the fluid takes.

 

I read the first couple of pages before I jumped to the end to see if the problem was resolved. Here's what happened to me. Bad steering stabilizer. My stabilizer failed and loss all fluid causing it to stick. It wasn't functioning smoothly so it would cause the truck to steer itself in every direction but straight. Try pulling the stabilizer off and checking how smooth it is.

 

Thanks but this is nothing like that. There is no sticking, It is like someone is pulling the wheel back and forth in a rythm. I have it narrowed down to the steering box.

 

It rained here today so I put my truck in 4wd and guess what, the jerking is back. I tried everything to get rid of it and its still there. After all this time of problem free driving, I wish I would have left it alone till winter. I still think its in the 4wd system but I did order a new steering box and will install it when it comes.

 

My 2002 PSD Excursion 4x4 had the same jerking steering wheel problem, 107k miles. Occurred pretty much randomly. I found there was one route I could take from my home – couple of turns, down a hill, 2 more turns - that could fairly reliably reproduce the condition. Two weeks ago it got worse. The following weekend I replaced the L/F caliper as it was potentially seizing up (on/ off hot rim & smell of brake material). While under the truck, I tried rotating some of the front axle shafts. They would turn by hand but seemed to have a few tight spots. I rotated the front drive shaft several times, tried the axle shafts again – they turned easier this time - and believed the axle u-joints were ok. Truck drove fine for the week.

Today I replaced the R/F ball joints – the lower one was shot and thought I’d take advantage of the long weekend. When I pulled the axle shaft, I found rotating the u-joint was a bit tight about one axis. Exercised it a bit more – and the joint froze about that axis. I had bought 2 u-joints just in case so now I had a chance to use them. Turns out the joint itself was rusted into the yoke – I couldn’t press it out. Ended up taking the shaft to my local Ford dealer and they removed /installed the joint and seals for a fee (ended up cutting out the joint! I live in Rochester NY – lots of road salt.).

When reinstalling the axle & hub, I turned the knuckle side to side to get to the hub nuts. I noted that the axle shaft would rotate to self align one of the u-joint’s axes to allow the knuckle to turn. That led me to believe the the u-joint could have a “random” influence on steering. I buttoned everything up and went for a test drive – down the “reliable route” to reproduce the to/fro steering jerk. No jerky steering! Granted, this was one trip but the problem didn’t surface. I hope my problem is resolved.

BTW – there was a tell-tale sign on the frozen joint that one of the bearing caps was bad – there was a light band of rust around the cap’s rubber seal.

I’ll let you guys know if the jerky gremlin returns.

 

That would be interesting. (the box).

 

Yes, let us know. My U-joints seem to be OK. They usually let you know if they are going bad by showing some rust or squealing (or clanking). One of my stub shafts doesn't turn freely as it should but I'm not ready to start replacing things in general.

 

My truck does not have one.

 

I've put 200 miles on the truck since the BJ's and front axle u-joint repair. Went down the "reliable jerking" route a few times as well. No sign of the gremlin.

 

I did this all months ago including changing the hubs. All went well but it always came back after a few hundred miles.

 

The gremlin has been gone for 3 days since I changed the PS pump but I won't claim a victory yet.

 

Wait for it...

 

It's been a week with no problems so far.The 2 changes I made were; new PS pump, and I ran it for 3 days with no hub on the right side. It's been back on for 5 days. The 3 washers behind the snap right seemed to have loosened up a bit. It acted up 1 time the same day I replaced the pump and it has been good since then.

 

Hmm... Interesting.