The front bracket on my Sidekick seat on my Nightster continually pops out under hard acceleration and also moves from side to side as the bracket is far too small.

After getting frustrated with the many "fixes" recommended, I thought I'd give Folkie's mod (XLForums) for the Brawler seat a go. Although not perfect or neat as Folkie's. the mod works perfectly. A few changes from Folkie's mod - I used aluminium (much easier to work with especially with my limited tools), used rivets and covered the entire bracket with a piece of bicycle tube to prevent the metal from rubbing,

Here's a few pics