No, you don't really have to undo the axle nut. I can't quite recall why I did it this way, I think I had problems with the clearance of the outer bushing bolt that holds the stanchion arm to the control arm.
If you only want to replace the lower arm there are just two bolts to the subframe and the ball joint. The ball joint can even be disassembled without any special tools. I wedge a flat wood chisel between the the top of the ball joint nut and the axle and use the force of the nut turning against the chisel to pop it out. There's no need to do anything with the strut.
I just found out why you need to removing the center nut. I tried loosening the ball joint nut with an open ended wrench, but it was starting to round off the nut. The ring end of the wrench doesn't fit due to the close proximity of the CV joint body so I will have to slide the CV joint back until I can get the ring on. Unfortunately I don't possess a 32mm socket wrench for the center nut so I have to pay a visit to the nearest hardware store - 3 miles away! Even more unfortunately, for a family that owns 4 cars, only one is at home and that is the Saab with just two wheel on! I suppose I could try that other form of transportation ........walking!
Just finished the job and thought I'd mention two points that could trip you up. Firstly, make sure you have a 32mm DEEP socket as the regular one doesn't fit all the way over the wheel center nut due to the CV joint threaded shaft sticking through it. (As mentioned previously, the CV joint has to be shifted slightly to make room for the ring end of a wrench to go over the ball joint nut).The second point (I don't recall reading it in the job descriptions) is that the control arm inner bush bolt should be tightened with the vehicle's weight on the suspension, otherwise the rubber is twisted beyond its designed angle and this will reduce its life. Other than that, and the struggle with corroded fasteners, the job was pretty simple. The old ball joints were indeed very sick!
You either have to remove the driveshaft (which entails buying a new nut for the end of it because they're not supposed to be reused) or just give it a good tug as dip says. I just tightened mine as much as I could with a regular wrench and my puny arm muscles.
If you start experiencing popping noises from the front suspension under acceleration/braking then you may need to give the nut an extra tug.
So I snagged this picture from another post, but it will serve my purpose. I'm replacing my son's right front lower control arm Saturday. Today, I crawled under it to survey the job. One bold/pin, appears to not have nuts or a bolt head on it. I'm wondering how it is removed?
I couldn't figure out how to put a picture in the post, but Ive attached one instead.
I took my control and stanchion arms off yesterday so I could replace the control arms and have new bushings pressed into the stanchion arms. I was a little nervous that the $50 Torx bolts would strip out, but they came out fine with a T55 Torx bit and a 1/2" breaker bar. The shafts were a little rusty, so I'll clean them up, and I noticed they had red Loctite on the threads, so I'll use some of that when I reassemble everything.