I have exactly the same issue.
Both sides.
Ive removed and swapped out both sides (shocks and springs), swapped springs, same deal. Tightened everything up to buggery. Same deal.
I 'think' its the coils binding on the rubber tophats under compression.
I.e. as the springs compress the top the of spring tries to rotate about due to the extra length, and the sound/knocking is the result of when the slip occurs between the spring and the tophat.
Im going so compress the springs and jam some grease/lube and see what happens.
Otherwise I'm totally stumped too
BTW, using KYB Supra shocks and Kings Lowered MX83 Springs
Bookmarks