Proportioning valves limit the rate of application, not the pressures. The rear brakes apply slightly ahead of the front to avoid swapping ends in slippery conditions. Does that training car have pressure gauges on both brake circuits? Somebody please measure those MC pistons and post the diameter differences.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!