04-06 STi caster adding lower control arm install! Less weight, better handling, more caster... What more can you ask for!
Shortly after lifting my Forester and figuring out that I wasn’t able to fit my newer larger tires without a bit of body modification, i.e cutting/hammering. I thought, there might be a better way. Understanding that Subaru had parts in their own bin that could help with this, I tracked down a set of 04-06 STi arms.
Caster is the name of the game, that 04-06 STi lower control arms bring to the party and will help fit your larger tires/achieve better turn/handling. Caster is the angle of an imaginary line through the tires contact patch and following the strut up to the strut top. When you lower caster the wheel is pushed towards the rear of the front fender, adding caster pushes the wheel towards the front of the fender.
03-08 Forester’s are not blessed with much caster and that isn’t a big deal. But if you lift them you will find that your caster has slid even further down the scale, pushing the wheel towards the rear of the front fender and can cause tire rubbing with aggressive tire fitment. With 04-06 Sti arms we will fix this issue.
This is a pretty labor intensive job and also passes through many bolts that have lived their whole life without being turned. Breaking off bolts is a moderate concern to this project, I would give yourself a good two to four hours for this job. It can go quite quick if everything comes apart easily, but beware of those rusty seized bolts/nuts/ball joints.
Your typical 3/8th and 1/2” socket set will be necessary. Your favorite ratchet, breaker bar, and air/electric tools to help rattle the stubborn bolts free. A couple of wrenches will round out your setup. Here are a few links to my favorites and most used.
Of course the parts listing includes 04-06 STi lower control arms. But if your lower control arm rear bushings (transverse bushings) are the original it is time to replace those. Part number for the STi arm is 20202FE800 for the right and 20202FE311 for the left.
The transverse bushing and mounts can be found new from Subaru. These are the 06-08 Forester version and the part numbers are 20201AC120 and 20201AC130. They are side specific so make sure you are getting the correct sides.
We will begin our install like any other suspension install. By lifting the vehicle and installing it on jack stands, then double checking our them before starting your work. With everything stable you can remove the front two wheels.
For your next step you can remove the axle nut with a 32 mm socket. This will insure that the axle won’t be pulled out of the socket when moving the spindle out from the lower control arm.
Next we can get underneath the arm and undo the cotter pin that holds the lower ball joint in place. With the 19mm nut removed we can break it free from the lower control arm now or wait for later. While you are in the area it is a great time to remove sway bar end links from the lower control arms.
Now because I was replacing both rear transverse bushings I went ahead and removed lower subframes from each. If you aren’t replacing the transverse bushings you don’t need to complete this step and skip past this. There are around seven bolts keeping each subframe in place, they are often very rusty given their low location on the vehicle. With the last bolt or two in you may want to situate yourself out from under or bracing the large subframe, because once the bolts are out it will be dropping in a hurry.
If you choose to remove the lower subframe you will now have plenty of space for replacing both the lower control arm and transverse bushing.You can leave the rear nut on the transverse mount because you will be removing them together and can take them apart outside of the car.
If you choose to leave the subframe in place and are leaving your tranverse bushings in place, now is the time to break the rear 22mm nut free. I often utilize a swift kick to get this nut loose as it is quite tight. You will also want to break the two 19mm bolts that hold the transverse to the body loose. This is necessary to help maneuver the lower control out with the lower subframe still in place.
Now we will come to where are two paths converge again. With the transverse mount dealt with you can move to the front bushing, it bolts through near the steering rack. It will be a long 17mm bolt, hold the nut side with your wrench and get the bolt spinning to remove it. With this out of the way you can now pry it out and be one step closer to removing it.
With the control arm loose of the inner two mount points you can either free it from the ball joint by giving it a few strikes from your favorite hammer. If you had broke the ball joint free earlier you are ready to free it and install the new unit.
You will need to make sure your STi control arms have their rear steel mounting arms for the transverse are installed in the same fashion. If the steel part is flipped on one side it will add further caster on that side (around.5 additional caster) and may caster a caster imbalance. You will also need to have the steel adapters that allow the ball joint to be installed on the STi arm properly.
If you left the subframe in you will need to install the control arm in the transverse mount first. With the control arm in the transverse mount you will shift it into place within the front bushing mount. You can now slide the bolt through the bushing to hold the arm in place. Lastly you will lift up the spindle and ball joint to install it into the control arm.
You can now reinstall the end links, making sure to run them completely down in order to keep them from knocking and making terrible clunking noises.
With all you bolts, ball joints and arms in their new homes you will take all the nuts and run them down. Having tightened all the bolts, nuts and cotter pins you can situate your transverse mounts. Pushing it forward on the chassis will increase caster and pushing towards the rear will decrease caster.
You are just left with the subframe if you removed it, placing the bolts back in their homes and running them down will finish that off. Lastly you will need to install your wheels, lower the car off the jack stands and torque those wheels down.
With all this done I would recommend a test steering back and forth to make sure everything is in it’s correct placement and not rubbing on to any components that may cause issues while driving. This would be a good time to take your car for a short test drive and listen for any abnormal sounds or steering issues.
As with any suspension change or install, you should have your alignment checked at the least. But for a modification like this you will need an alignment. For my vehicle I saw toe move out on both sides. This is also an excellent time that you can have your caster shifted to suite your setup.
Congratulations on the install! You can now enjoy better steering, a slightly wider track width and less rubbing if you had installed larger diameter tires. You also subtracted a smidge of weight from your control arms and strengthened them up! They are also a bit easier on the eyes when underneath the car!
Amazon tool links
Subaru part numbers!
06-08 Forester transverse bushings 20201AC120 and 20201AC130
04-06 STi aluminum lower control arms
20202FE800 for the right and 20202FE311 for the left.