What is the purpose of control arms after a lift and if i purchase them do i need to get upper and lower control arms for the rear and front??

 

they are to help with you castor angle and driveline angles. i hate to be that guy that says use the search function, but you can find more info that way than i can provide. try searching for
castor angle
adjustable control arms
pinion angle

 

the lowers will allow you to reposition your axles to where they need to be and the uppers will allow you to dial in your caster up front and your pinion angle in the rear. depending on what kind of arms you get, they can also provide a whole lot more flex and are typically stronger than stock.

now, if you're only going to be lifting your jeep about 3"-4", all you really need is a set of adjustable lowers as they alone will help you to set your caster and give you a much better ride. if you have a 2-door, you will need to get a set of rear adjustable arms so that you can set your pinion angle to accomodate a new u-joint style drive shaft and trust me, you will want one sooner than later.

 

Maybe I'm search deficient but I have been unable to find specific information as to why upper arms are recommended on the rear instead of lower arms?
As you can see from my footer I have a TF 2.5" spring lift and have ordered TF front lower adj control arms to fix the caster in the front. I would like to put lower arms in the rear as well to correct pinion angle and move the axle back to make room for bigger tires. Is this possible with the stock rear drive shaft?

 

for the amount of lift you will be installing on your jeep, no adjustment will be needed for your lower rear control arms. in fact, if you installed a set with the hopes of setting your pinion angle, you would have to shorten them up quite a bit and i can tell you that it is physically impossible to do that. and, even if you could, you would effectively be pulling your axle far enough forward that it would cause your tires to hit the pinch seam big time. if anything, the taller you go, you'd want adjustable lower rears to push your axle back a bit and get it positioned back to where it needs to be. as far as adjustable upper rear arms go, they will allow you to lengthen them enough to raise your pinion up and in line with your aftermarket u-joint style drive shaft and without moving the position of your axle. does this make sense?

 

Maybe I have spent so much time trying to figure out what positive caster is and why I want it that I have not paid as much attention to pinion angle and the rear. Is it the design of pinion angle and the job of the rear control arms to match the angle of the rear drive shaft? (straightening the angle of the U joint?)

It seems like you are saying that to move the rear axle back now I would need to get a new drive shaft, upper and lower arms? But since I am only running a 2.5" lift (3.5" in the front) that I really don't need to worry about it yet...???

 

i apologize for confusing things for you.

if you are getting a new u-joint style drive shaft, you will need to get adjustable upper control arms as they will allow you to rotate you axle up and put your pinion in line with the drive shaft. you will need to do this in order to prevent drive line vibrations. does this make sense?

adjustable lower control arms allow you to reposition your axle after lifting it and upper allow you to rotate it around. if you had both adjustable front uppers and lowers, you would just adjust the uppers to give you more positive caster (what is needed to get rid of flightly steering). however we have found that if you are on a budget, you can install just a set of adjustable front lowers and they alone can give you the caster you need. does this make sense?

 

no worries! this forum and yourself have helped me greatly many times! and I appreciate your continued help and patience!

I am not planning on getting a new drive shaft. I was just wondering if it was possible to move the rear axle back with just control arms? It sounds like it is not possible and I shouldn't worry about it until I go higher... Right?

yes this part makes sense! I think I understand the front better than the rear. I have a bit of flighty steering and I hope the TF front lowers that I have on order with Northridge will help with that.

 

you mean rear upper adjustable control arms with the new u-joint style drive shaft? the rear drive shafts from je-reel and woods are they u-joint style?

 

while new adjustable lower control arms will allow you to push your axle back, there is no reason to do this with just 2.5" of lift.

adding a degree or two more caster will help get rid of the flighty feel

yes they are and yes, that's what you will need