How do I know if my u joints are bad???

Take a pry bar or flat head screw driver and carefully put it between the the yoke and driveshaft and check for movement. Are you getting any noise from it? Mine had a seized joint and was clicking however I had to take the driveshaft out to realize that.

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2005 Ford Ranger XLT Extended Cab, 4.0L. 245 Cu. In, 5-Speed, 4.10's, KYB'S @ corners, Moog Hubs, Rain Guards, and Mobil 1 for life.

Mine made a clunk type noise while accelerating. I would do what Matt suggested and check for any play.

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2002 Blue Edge <-- Retired off road toy
3.0 Automatic, 2wd, 4:56's, 35x12.5 Kuhmo's, Lifted 2x, and more. TOTM July 2015
2002 Jeep TJ <-- NEW off road toy!
2.5L 5-spd, Skyjacker 4.5", 4:56's, Aussie Lockers, 33x12.5's, and more.
Build Thread --> http://www.fordrangerforum.com/proje...blue-edge.html
Youtube --> https://www.youtube.com/user/smashlizard

When I accelerate it jerks is that what I'm looking for?

Jerks? That sounds like a engine/tranny problem, not suspension.

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Ford Ranger XLT 4x2 Supercab 4.0L SOHC | 5 Speed Manual

3.55 Open | Built December 15, 2011

Dynamat-Doors | MB Quart DKG Speakers | Ford Bedliner | Ford Hood Deflector | AVS Window Deflectors

Wonderfull lol

Prob just u joints. Check them like stated above. Mine jerks also when pulling out and getting on the throttle. Not hard to replace.