Air Controlled Dump

If you have a suspension dump valve on your trailer it probably doesn't matter. Since you're dumping for loading dock heights, it makes sense to apply the trailer brakes.

 

If you have separate suspension dump valve, I would dump the sus. first and after it is empty or all the way down, then I would set the trailer brakes. That way they are not fighting each other. Not sure I am saying it right. If the suspension is 1/2 way down and you set the brakes, the will hold the suspension in that position and then when they drive on the trailer the weight on the fork truck is going to put pressure on the brakes. The noise you hear is probably the brake shoes turning in the drum.

 

Set your tractor brakes up, lower your trailer to where you want it, then have both tractor and trailer brakes set up for loading.

 

Ok dump the manual valve let all the air exhaust out of the bags, then set your trailer brakes. If you look at your suspension when it is all aired up, then when you set the brakes before the bags are empty, and then when the bags are totally empty you will see what I mean. The brakes will actually hold the suspension up if you set them before the bags are completely empty. Hope this helps. I am just having a tough time putting it into words.

 

Edited.... never mind