I remember reading up on an article on these many years ago. Essentially they alter the oil pressure required to shift the gear, aswell as changing some of the valves and internal oil galleries which dictate when down and up shifts are performed. You end up with an auto that is alot firmer in its gearchange, also reduced heat as there is much less clutch over-lap when changing gears, especially 1st-> 2nd upshift. The downside is increased load on the tailshaft and diff.. not a huge amount, but some none-the-less.
Last edited by voxbox; 09-12-2008 at 12:00 AM. Reason: it's after midnight and i'm forgetting words.
Pretty sure they're only like $90 from most places, not like $120 (incl. post) like on Ebay.
Better off with a Transgo kit though. Spend the extra $80.
STLNUP: did you mean shift-kits in general, or the B&M ones specifically? :P
Vox in general
Well there's nothing wrong with them per-se, but they will increase shock-load on the rest of your drivetrain. Guess it depends on what you want - if you want something that has soft changes then keep it as is. If you want crisper gearchanges, throw one in. only takes an hour or two to install it, and wont adversly affect the life the box.