because of the oversized wheels and tires as was the nylon and pot metal-geared differential. The Re=release versions of the newer ORV chassis cars received updated axles and area a huge improvement. The re-release Frog got dogbone style axles, and the Monster Beetle, and Blackfoot re-releases got a CVD style axle. The pot metal parts generally wore out before the nylon parts did. This was attributed to the soft aluminum side plates of the transmission, allowing the differentials bevel gears to flex outwards under load, minimizing gear tooth contact with the differentials spider gears, resulting in the dreaded differential "Clicking" as the gears would skip teeth under load. This was commonly patched by installing 5mm I.D. shims between the bevel gears and differential output bearings (The Monster Beetle had differential bearings stock, The Blackfoot had to be upgraded to ball bearings to do this modification, as side loaded bushings would just get destroyed in a short period). The best known to date upgrade to fix the differential problems is solved by using the "MIP Ball Differential Kit" (MIP Part# 16210), note that is must be used with the re-release axles, and not the original hex drive axles. Miniature ball bearings were an extra cost option to replace the nylon bushings packed with the model for both the transmission and wheels, but were a necessity since rapid wear of the bushings meant a complete overhaul of the transmission and partial disassembly of the rear suspension unless the kit was assembled with bearings from the outset. The expensive, heavy plastic bodies (with a replacement cost roughly half the price of an entire kit) made the model prone to rollover, eventually resulting in a badly scratched, unattractive replica. The tires themselves, even the spiked ones, were basically unsuitable for the off-road situations that the kit was intended for. Several R/C companies rose to the challenge, especially four Southern California companies: MRP, Pro-Line, Thorp Corporation and Robinson Racing. MRP specialized in heavy-duty modified parts, Pro-Line was (and is) a highly regarded manufacturer of R/C wheels, tires and bodies while Thorp and Robinson engineered expensive but rugged differentials and axles, allowing the use of much more powerful, R/C-specific motors than the Mabuchi RS-540 shipped with the kit; this motor was originally designed for use in heavy-duty computer printers. A North Royalton, Ohio-based company, Parma Corporation, made a series of replacement bodies vacuum-formed in lightweight, clear