I don't consider the Allvit's drop-down knuckle to be a bash-guard, if anything the longer knuckle only adds leverage to bend the dropout hanger if the bike tips over.
But the normal, later Allvits did "fill in" the simpler early knuckle by maintaining a U-shaped cross-section, which provided support to both ends of the main para arm's bushing while taking away from it's minimalist form. I personally think that this re-design of the B-knuckle was unfortunate, though I am still a fan of the Allvit, modifying them for 6-speed operation (not such an easy task) on several occasions.
The Svelto's disadvantageous travel path with respect to the freewheel's contour will be more of an issue with modern chain, which is much more flexible. But it still can shift well with the right combination of chain and right-sized freewheel.
Thanks, Mark, for your excellent illustrations!
I've used Allvit's on 30t freewheel cogs, though once had to dremel a slight divot into the top edge of the outer (driveside) cage plate for clearance.
If one simply starts with an Allvit in good condition, then there should be no need to do anything to it other than to install it and apply a little oil once in a great while (though dependent on riding conditions of course).
Alvits were
doubly shamed because of their being installed on so many low end bikes. Firstly, these bikes gave the product a lowly image, and secondly these bikes tended to be so poorly treated so as to prevent one from conducting a proper evaluation of function.
Schwinn also spec'd Shimano-made derailers on some of the same bikes that might have featured the Allvit, and which did actually have a dedicated bash-guard plate that could only be considered to be an added appendage versus simply being part of the B-knuckle. These are sometimes confused with the Allvit, as both have acres of chrome and bear Schwinn-Approved branding.
In either case, with the top "B"-knuckle always taking the hit, I fail to see what would ever actually be protected by any sort of additional leverage added to the top knuckle(?).
And, (only in in the Allvit's case), the wrap-around knuckle cross-section stiffened the long knuckle and added paired support to the pivots.
Shown here, in modified (6s) form on a nicely-maintained bike, works very well but the cable travel at the lever does become non-linear in a longer-travel way as the beyond-spec sixth (largest) cog is reached for. The Twin-Stick lever handles this amount of wrap, if barely.
