Re: Brill Radiax trucks

The last Brill Radiax truck built was for the Third Avenue Railway System in the USA.   It went under a Brill “convertible” Master Unit ca. 1930.   The car was not successful as it derailed on anything but the straightest track.  The car was sidelined within a few years.   Some of you may remember the “Pivs” or Pivotal cars in Leeds, England.  The “truck” was two independent wheel assemblies that were linked together with tie rods.  As the car entered a curve, the 10’ truck would pivot using wheel flanges to steer.  Apparently it worked while the cars were relatively new, but as the linkages and wheel flanges wore, the wheels did not pivot into the curve but the flanges cut into the rail head.  Eventually all of them were reworked to eliminate the pivoting mechanism, becoming the “rigids.”   Many of the cars were re-trucked.  

Every now and then the idea gets retried - prototype Variotram/Variobahn Tw601 that was the 'prototype' the Sydney cars were based on was fitted with a weird motor bogie steering arrangement where the wheel motors could turn into a curve. It appears they were trying to address the problem with the fixed truck multi-artic design where the forces on the lead bogie in curves lead to them eating the track. But it led to instability and derailments so CVAG locked the pivots to keep the axles straight in the bogie frame. The car lasted near 20 more years before worn wheels and a crack in the trailer bogie frame got the car withdrawn (and subsequently broken up).

The first photo shows the whole bogie and you can see where the damper/centring spring went on the tie bar. The 2nd shows the pivot. It wasn't free to move much, but it would have made some difference to the ability to track curves. Turns out what it did was enhance it's derailment ability.

The 'production' Variobahns had a different bogie and were not interchangeable with the prototype car. The Sydney cars were different again.