Like many of you guys with XJs Ive had a mystery clunk in my front end when the suspension cycles.  Ive had the wheels off three times looking at everything.  I finally decided to replace the bushings in the lower/upper control arms as well as the track bar bushing.
 
I started with the lower control arms.  The factory bolts were frozen with corrosion and wouldnt budge.  My Sawsall and a Torch blade took care of the bolts.  The bushings were also frozen in the control arms and would not come out even with my 2,000 pound arbor press and a three-foot bar and a lot of PB Blaster.  I cleaned out the Blaster after long periods of soaking with brake cleaner and compressed air and then squirted in some CLR and watched bubble for several minutes, it worked but when they let loose it sounded like a hand grenade went off.  Save your money up and just buy new control arms if you live in the Rust Belt like I do.  A fairly easy job turned out to be a giant PITA.

After replacing the bushings in both lower control arms I took the Jeep for a ridethe clunk was still there.  I decided that I would build a ramp using 2X12s by three-feet and 2X4s that my trusted helper could drive up on then drive off (carefully) while I would be looking and listening under the front end.

Before doing this I decided to look one more time.  I went over every square mm of every component.  With a bright flashlight I notice a tiny shiny spot on one of the bolts that hold on the steering box.  I have aftermarket Hi Country tow brackets that wrap around the frame and are held on by the steering box bolts.  I couldnt see or feel if there was any wear on the sway bar but after using a mirror I saw that the paint on the sway bar was worn off.  I confirmed the contact by taping a piece of paper to the sway bar and taking the Jeep for another rideyep, there was a slight tear in the paper.  I fixed the problem by removing the washer and grinding down the bolt head about a 1/16th of an inch.

TIPS:  If youre going to tackle the control arms, do one side at a time.  The front axle will move when the bolts are removed.  I didnt have a tapered rod and a helper at the time so I used a floor jack and a come-a-long to realign the holes.  They have to be aligned perfectly to get the new bolts through the holes in the brackets/bushings, especially if you replace the factory bolts with grade 8 9/16-12 bolts (theyre a few thousandths bigger in diameter).  Leave the bolts/nuts loose (finger tight) then put the wheels back on to put weight on the suspension, then cycle the suspension up and down and sideways several times.  Then torque to factory specs (85 ft/lbs.) I torqued mine to a little better than 90 ft/lbs. because I used anti-seize on the threads.

If you replace the factory bolts with grade 8 US bolts use anti-seize on the bolt shafts because if you look at the factory bolts youll see that the shafts are smaller in diameter except for about 3/8 near the cap end and the threads.  Im sure they did this to keep the amount of contact between the bolts and the sleeve in the bushing to a minimum to prevent seizure (didnt work on mine).  I found my replacement bolts at a local ACE Hardware as well as some grade 8 nylon stop nuts.  Grade 8 bolts arent quite as hard as factory bolts but still have a rating of 150,000 PSI of shear strength and should hold up fine.