How do you replace the lower suspension arm on a nissan primera?

Answer 1

the most simple answer is: you remove the old one first, then replace it with the new one.
the more complicated answer is:
1. you have to jack up the car (car on handbrake, jack at factory prescribed point, or use a (stable!) garage bridge. the wheel in question has to be fully off the ground, not carrying any weight. This will make the suspension (plus spring) drop a bit. Take off wheelnuts. Mind that you put the wheel underneath the car so that if it drops by accident it will not drop on your leg or torso or head.
When the wheel is removed you see the brakedisk, wheelbarings, axle, transaxle, suspension, spring, steering bar (rod end), brake cables.

2. Remove the brake cable (hydraulic cable) from the supports which in normal use keep it away from the turning wheel. Do NOT take off the cable connectors, just the supports. This will make it easier to manouver the suspension arms and lower the lot further. Be aware that brakelines should not (never) carry the weight of the suspension or they might rip - so notice the length of the cable when the suspension drops. BTW Always test your brakes before driving away after your repair is done. Working on your brake-suspension related parts can sometime cause air to enter the brakecylinder.

3. the fusees is where the wheelaxle, steering rod and trans axles come together on a pivot which is able to go left/right (steer) and up & down (suspension). the lower suspension arm is the part which stabilizes the movements of the wheels and suspension. it's like the thing which keeps it "in place" and "steady", supporting the changes in direction caused by steering and holding the wheels in line whilst suspending. BY REMOVING OR CHANGING ANY OF THIS YOU WILL AFFECT THE DRIVEABILITY OF ANY VERHICLE. in other words: fack this up and you'll end up in a tree. If you are not sure what you are doing: use a garage specialist. A suspension arm costs about 50-100, it takes an average mechanic about 10-20 minutes 30 max. so do the math.

4. If you are sure what you're doing, (and have the proper size tools) you can remove the lower suspension arm by disconnecting the bolts which connect it to the car) engine side) the removing the bolts which connect it to the wheel/fusee side (tire side). These bolts are normally tightened with 200-300Nm (very tight) so make sure you have the proper keysize (or you'll brake the bolt head and risk having to replace the whole fusee cause it's not an easy cut.) Use WD40 to let bolts relax when removing (rust can make them brake easily). Warm up with a gastorch (not a plasmatorch) or give them a soft tap with a hammer if they're stuck.

the fusees are cast-iron. cast iron is very strond but can break when hammered upon in the wrong spot so go gentle.

when the bolts and nuts come loose: the suspension and fusees will drop (or slide sideways/outward). Watch that brakeline. Tape, wire, or support the lot in place for a second whilst you're working on removing the suspensionarm's both sides/ends.

5. inspect the nuts and bolts which come off the unit. You might want to replace them if they come out rough. Your life will depend on it: if they break after reassembly whilst you're doing 90 you cannot steer any more (again, that tree)
for the price of about 3-6 dollar each you might want to replace them anyways. Never use different size or specced bolts than the original.

you might have to remove the tracking rod from the fusees (the thing which makes your car steer left and right)
MAKE A MARK and/or count the number of full turns you have to do to remove the tracking rod. not doing so beforehand will mess up your wheel alignment after you've put it back on. This is the kind of stuff which is sensitive to millimeters. I always twist the bolt that secures it clockwise twice (so away from the rodend), then remove the rodend anticlockwise leaving the securing nut on, with a tape, only 2 turns away from it's original position..)

6. put the new part into place. make sure you inspect it's proper size, compare modelnumbers with the original, use some coppergrease (not oil!) on bringing it in position. put bolts back in WITHOUT the nuts or the nuts "handfast".

7. Check position, put tracking rod back on incase you removed it.

8. put nuts on bolts with the proper tool, tight as you can, check factory specs, this is not the bolt or nut you'd want to loose whilst driving. I usually put my full bodyweight into pulling them tight. Anything less is not enough.

all done? put brakelines back in supports, wheel back on and TEST brakes before you hit the road. you might want to bleed the air out of them anyways.

BTW replacing the lower suspension arm does NOT mean the whole suspension assembly (shocks/springs) have to be disassembled. be aware that the nut keeping the suspension-SPRING (the one which normally carries the car) has enough strength to blow straight trough a wall. NEVER take the nut of the top of suspension SPRING/shock assembly, the nut holding the spring ON the shockabsorber. (so thats not the ones holding it onto the car)