Doesn't the yellow parking brake engage both tractor and trailer parking brake system?

 

Uh, not unless your trailer is non airbrake. Have to pop both to lock both. With my truck, I pop the yellow service one and the red one pops automatically unless I physically hold it in with my hand. Yellow is normally your truck only.

 

Hm,why does the red one say "trailer supply,not for parking"????

 

Because it encourages people to set the tractor brakes the way they should? It may be a throw back from when there were not maxis on the trailers, air bleeds out of the trailer.. it has no brakes and the truck and trailer roll off without you.

The only truck that I ever drove that set both tractor and trailer was a 71 Ford Cabover.. it had a locking lever to release or set both at the same time, there were no "buttons".

 

All of our tractors at school, 99 century, 2001 Columbia, 2004 Columbia pops both out when you pull the yellow knob.

 

All the tractor unit's I've driven did that (International, Kenworth, Peterbilt, Freightliner, Ford). It's apparently the "default" setting, if you wanted to just set the tractor brakes, you held the red button in while pulling out the yellow.

 

the yellow knob will not lock the rear axle only the front rear. on mine anyway. you can tell by looking at your brake chambers. the 3030 brake chambers are the ones that lock the others dont.

 

Ok I got it now,so in order to leave parking brakes off on trailer during freezing temperatures you just hold in the red one while pulling the yellow one.
Assuming there's no air leak trailer parking brakes will stay off right?

 

Right. make sure your tractor brakes are adjusted properly

 

Ok,thanx this forum is priceless.