[lifespeed]

Agreed, not to mention the bendy axle problem with C-clips introduces camber change so simply going to a floating axle is a huge improvement.

I am looking into replacing the factory 8.8" axle in my 2004 Mercury Marauder with an aftermarket full-floater Ford 9" for various reasons mostly related to durability and handling. A few years back I updated the suspension with larger tubular anti-roll bars, Penske 7500DA shocks, billet aluminum rear control arms and Watt's link. It works pretty well (except for the axle shaft wear and other issues), but I did have trouble with rear shock tuning and air spring rate, having to soften them quite a bit. I came to the conclusion the urethane bushings were worsening the inherent binding in the factory parallel 4-link.

So, if I'm going to all the trouble to put a different axle in there I may as well give some thought to things like the roll center location set by the Watt's link and the 4-link binding.

I was thinking of using a stock car (late model, modified) suspension cage or birdcage instead of welded-on brackets to mount the 4-link. These have bearings between the control arm brackets and the axle tube. They can also include brake brackets. Seems pretty appealing, not to mention saves a bunch of fabrication. What could possibly go wrong? If I am not mistaken, floating the control arms on the housing also eliminates the inherent bind of a parallel four-link (trying to twist the axle housing as a sway bar). I understand I will have to install a torque arm. I believe the dirt-track approach with the torque arm mounted to the chassis with spring and shock is not necessary or desirable for a pavement car. Brake torque can be applied through the control arms via a birdcage incorporating a caliper mount. This seems reasonable enough.

Has anybody done this? Can they hold up to street use and live a reasonable lifespan? I'm pretty sure they run these things on dirt tracks too and are sealed against grit and grime. I do plan to retain urethane bushings on the frame end, using rod ends at the axle end.