releasing brakes on front axle??

I'm not sure which axle its on.

My electric valve for the axle dump is on the rear axle. I also have a manual valve that dumps both axles on the rear of the trailer.

 

every truck i've driving with a drop axle. pushes the brakes. tires down or up.

so why worry about brakes being applied if the trailer axle is lifted?

 

It will pull a LOT better with the brakes released! Lots easier on the tires, too.

 

I don't think it's law that we require the brakes to be disabled... I know one some of our older trailers they brakes stil applied when lift axles were up.. It would be a PITA when you hit a high spot on the road (especially if you were loaded and had them lifted turing a corner).. The tires would get flat spotted, scuffed and you would have a few seconds of resistance as well... We also have older trailers where the brakes on those axles are disabled when lifted.

Now since SPIF came out in Ontario the axles all have disabled brakes on lift axles when they are lifted up... Although these new SPIF axles are not allowed to be controlled from the cab because when you loaded and using them they must be down all the time.. Since the whole point of them is to keep the weight on ALL axles during turning whereas the older non-steer axles would need to be lifted which would put all the extra weight on the rigid axles... The only way in Ontario your allowed to have SPIF axles lifted from cab is in off-road applications and where you have extras axes for "out of province" use...

So having disabled brakes is actually a good thing because when you hit a high spot on the road the tire will just rotate like normal.. If the brakes aren't released then the tires have no where to move so you end up creating flat spots and scuffs over time..

I guess cause most of the U.S is only running on 5 axles, lift axles aren't as common as they are in Canada... I think the rule of having the brakes still working when axles lifted is pretty stupid because the axle is inactive so what good is it to have functioning brakes on the lifted axles.. I guess if it was a factory option it would be ok, but since most of your dump valves are homemade you wouldn't get away with it.. It's not really common to see dual axle trailers having dump valves on them (other then to released pressure from all bags when dropping trailer) but then again spread axles aren't they common here in Ontario....

 

http://www.trucknews.com/news/saf-h...uspension/1002364749/?ref=rss&ctid=1002364749

 

Having them enabled or disabled makes a big difference just like GOV Trucker pointed out. Take my Utility reefer for example. I only have about 3-4 inches of clearance between the tires and the road when lifted. Get to a set of railroad tracks or most major intersections that are rutted up and a person can see where the lift axle tires would drag with even a lite brake application. The Hendrickson under beam lift kit I just purchased for the trailer actually includes a valve to disable the service brakes on the lift axle when in the up position.

 

Well perfect example to have released brakes today actually... I went into one of our yards to get fuel... Well I have a walking beam uspension steel trailer so it rides a little lower then air-ride the 2 lift axles are obviously airbag...Well when you leave this yard into the road, the road has a pretty big hump in the middle when making my left turn... Well when you loaded at 115,000 lbs with 62,000 lbs of material in the box the turn is not very nice... Even with the brakes released (I couldn't only imagine what it would be nice if they were locked brakes) I still had the back of the truck hop because the massive amounts of friction when the tires hit the hump.... They have no where to go cause they are lifted up as high as they go, so when they hit that hump it's just hitting something... It's almost is enough to stop the truck acutally, but I have had it do the hop and skip of rear tires because of it.. I don't like it cause I don't want to snap a driveshaft or grenade the rear end..