Jacking trucks and trailers with air ride.

[Truck Shop]

One item I have never seen posted on here is raising a truck with air ride trailer connected. For those who
haven't experienced what happens when the steer axle is jacked and a stand under it with trailer hitched to fifth wheel.
If only the yellow tractor valve is pulled and the red trailer valve is in {brakes not set on trailer} and the air ride
height valve is not plumbed to a emergency tank to keep air in suspension air bags when air is dumped or air
bleeds off the trailer will creep forward as it sinks down. Also pushing the tractor with park brakes set forward.
It can and has pushed steer axles off the jack and tipped the stand-if one was used. Some trailers come with
swing down stiff leg that swings into place on axle air bag saddle when air is emergency/red valve is pulled
to stop trailer from sinking down but most trailers with air ride don't have it. A loaded trailer sinking down
can push the tractor ahead 3 plus inches and shove it right off a jack. Very dangerous so always pull both valves
to be safe.

 

[crane operator]

Thanks for posting truck shop. A air suspension dolly for a trailing boom on a crane was my first real foray in air suspension. I learned real fast in picking it up and setting it down how much forward and back movement there was in the air suspension. Trying to line it up at a set distance from the turntable was a learning experience.

My lowboy will really push the truck back and forth with dumping air, I guess I never thought about it in regards to bleeding off slowly while a jack was under a axle, but I could easily see it pushing one off.

That's two things I learned tonight!

The other one is in the thread where they are talking about the heating joints. I hate to admit it, but I have never used a shield when working with a press. I don't do it as much anymore, but when I was working agriculture, we were always rebuilding gearboxes and taking bearings off shafts in the press, and I never once thought of a shield on the press.

 

[RZucker]

When working with air ride tractors I have always dumped the bags before jacking the front end. Don't need the front end getting dropped of the jack stands.

 

[petepilot]

dropping a spread axle loaded trailer without first dumping the airbags will ruin the landing gear very quickly also . most newer ones auto dump,

 

[terex herder]

Often called "dock walk". There has been more than one fork lift driver discover it the hard way. Setting both sets of brakes isn't enough. Typically, the tractor only has one axle of spring brakes, where the trailer has two. Best bet is drop the air in the bags, if it has a drop valve. Otherwise, chock the tractor.

My air ride trailers specifically say to drop the air suspension before unhooking to prevent dock walk from collapsing the landing gear.

 

[Wes J]

I worked in a shop where a truck slid off a jack while the steer axle was up to grease it. The brakes were released and the mechanic forgot to chock the wheels. The hood was open. The floor was sloped to a drain in the middle of the shop. The rig rolled forward into another truck and damaged the hoods on both. No one was hurt.

We always greased the S cams with the brakes released and the king pins with the axle raised. All was well if you properly chocked the wheels. One little mistake...

 

[Wes J]

Best bet is drop the air in the bags, if it has a drop valve. Otherwise, chock the tractor.

My air ride trailers specifically say to drop the air suspension before unhooking to prevent dock walk from collapsing the landing gear.

Probably a good idea if the trailer is loaded.

Another point: on a short trailer like the dump trailers we use in this area (typically 20-24' total length) if you drop the trailer with the bags full, when you go to hook up the next time you'll find yourself cranking the landing gear down considerably to get hooked up. It can be dangerous if a guy doesn't pay attention and sets the king pin on top of the locking jaw and tries to pull away. Ask me how I know that...

 

[Truck Shop]

That's why most every dock has the retaining hook to the ICC bumper to stop dock walk especially forklift accidents. Any time wheels are removed or rig jacked we
slide rubber chock blocks to the wheels. We have had a few high pinned when backing under, just installed a fifthwheel rebuild kit 3 months ago on a tractor with
25,000 miles on it at the time. But any of that can be solved by getting out to check fifthwheel height before taking it for granted pin height is correct. Then physically
look to make sure the fork bolt is retracted on the fifthwheel to know it's locked then tug on it a little.

Truck Shop

 

[Wes J]

But any of that can be solved by getting out to check

That doesn't sound like any truck driver I know... Especially the getting out part...

Long ago we had a yard truck with a 5th wheel lock you could release with an air switch inside the cab. I hooked it to a trailer at the end of the day and left it for the night. Next morning my coworker pulled the trailer into the shop. I guess I didn't get the latch set when I hooked and the trailer slid off in the yard. Luckily it was empty and moving slow. We just raised the landing gear and rehooked and went on with our day. But he was not too happy with me.

 

[Truck Shop]

https://ktvl.com/news/nation-world/2-men-crushed-under-bus-at-seattle-repair-shop