Castor correction bushes are limited to about 2 degrees of castor correction, OK for a 2" lift but not nearly enough for a 4" lift. They work by twisting the front diff back to compensate for the forward twist caused by the lift. Correction bushes do not correct the alignment of the radius arm which will be in a droop position after the lift putting stress on the rear mounting bush.Originally Posted by HippoNZ
Drop arms replace the original radius arms and are shaped to put the front diff back in correct alignment as well as keeping the main part of the arm in the original (horizontal) position taking stress off the rear bushes. Most drop arms also move the front diff forward about 13mm as well.
Drop boxes relocate the rear mount of the radius arms approximately 90mm (depending on what drop boxes you get) below the original mounting point which puts the radius arms and therefore the diff back close to correct alignment. Most drop boxes also move the mount forward about 12mm as well. giving better wheel arch clearance for bigger tyres.
Tony
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