I need step by step instructions on replacing front lower ball joints on a 1996 GMC JIMMY4X4.

Lower you can do fairly easy. Upper, a bit tougher.For the upper you will need a spring compressor.

Upper ball joint knuckle nut 60 ft lbs, lower ball joint knuckle nut 80 ft lbs....mounting nuts and bolts 17 ft lbs

replace left front lower arm ball joint Anon, Link shows how to replace lower ball joint it is a Lexus, pretty much identical to your lower suspension. Check the attached links,instruction and guides, Good luck
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How To Replace Front Lower Ball Joint
http://z4.invisionfree.com/lexusaltezzaclub/ar/t9466.htm
Moog Balljoint amazon review Lexus IS300
2001 Toyota Altezza lower ball joint Google Search

Lower ball joints attach the lower "A"-arm to the bottom of the strut assembly or steering knuckle. Original ball-joints are usually rivited on and require drilling or grinding to remove. The vehicle must be raised and supported when doing this. Seperating the balljoint from the knuckle requires a splitter fork and a lot of pounding. Not something I would recommend for a novice to attempt.

check your rotors

15 or 17, there not enough difference to worry about. make them all 15

I've replaced many ball joints, and never used a torque wrench. Just make them tight. If yours are the type with cotter pins, then you make it tight and slip in the cotter pin.

There is a large amount of stored energy in the spring. you can easily be seriously hurt. If you are asking this question, get a shop to do the job. It absolutely, positively must be done correctly or you risk loss of control of the vehicle.

is this a 4 wd drive unit or 2wd unit? are you mechanically inclined and have basic common tools including a jack and jackstands? if you live close to pep-boys auto center then you can take it there you will spend about 200-300 to do the job, just ask them for a qoute first and that hopefully is still free. they have a special coupon on there wbsite right now that will save you some money, plus if you are over 55 or student in school you can also save money there. i was a service manager there for a while... let me know what you want to do they are not super hard to do but can give you a headache if you dont have a grinder or chisel. i can walk you through it though if you still wish, im all for the do it yourselfer.