37 years ago, Finke NT

Haulmark experimented with various combing rail sections. We had the Freuhauf rail originally but after one season it was replaced with RSJ.
My last trailer was all RSJ and also had the bell crank suspension. ( no photos though)
In the NT photo you can see the tie rod running between the cranks.
It was supposed to give more oscillation than the rocker beam style but didn't make any difference, weighed a touch less.

Reckon this might be the same Mack as in Roderick's original post, was on display at the Gatton Qld transport museum April 2013, chers Pat

My simple photo taken in passing has resulted in some very interesting technical information, and now the history too.
What great additions, thanks for posting.

Roderick B Smith
Rail News Victoria Editor

...well done fellas .. cowl mounted mirrors were the heavy duty option on Kenworths in the 'States and every conventional Kenny out here have them as original equipment, so this Mack being a big banger on outback work probably had this set-up due to the fibreglass doors being fitted from new

...there also appears to be a vent in the RH cowl panel....something else i've never seen on these before....