Question:
I was in a truck the other day that had a switch on the dash that said fifth wheel lock/unlock.Is this for sliding fifth wheel or a safety device for release lever.I don't think this truck had a sliding fifth wheel but don't know never seen one how can you tell.I know I'm supposed to know this but am a very new driver and trucks I have drove never had this until the other day.I posted this on another site and all I really got for an answer was an argument so thanks for any help. Oh and by the way,Hoss I think your way to cool.Thanks again.

Answer:
Most of the time when you see a switch labeled like that it is for a sliding 5th wheel.
Some examples of what an air slide 5th wheel looks like:
Some have big slots like in the 1st image and others are like the other two. If you do not see anything like that then the truck is not airslide equipped.
Answer:

That's a switch for your 5th wheel slider. It unlocks the slider so you can adjust the 5th wheel to add or subtract weight off your steer axle.
Usually, 1 notch is 250 lbs. (from what I hear)
I have a 'slider' 5th wheel on my truck, but the guy that owned it before I bought it, welded it solid. He did a good job at it though........I've never exceeded 12K on the steers.
NOTE! A sliding 5th wheel plate DOES NOT add or subtract weight off your drive axles!

Answer:
When the switch is in the unlock position, think of it as activating a big electromagnet that pulls the pins so that the 5th wheel can be moved. When the switch is in the locked position, the pins will securely hold the 5th wheel in its current location.
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The switch is kind of like a parking brake for the 5th wheel. Your parking brake does not move the vehicle. When the parking brake is released, it allows you to do something else that will move the vehicle. When the parking brake is activated, it does not allow the vehicle to move.
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I hope this is not to simple an answer that answers the question that you asked.

Answer:
I believe that moving the 5th wheel one position shifts approximately 500 pounds. Sliding the trailer tandems shifts approximately 250 pounds per hole.

Answer:
The exaxt amount of weight shifted depends on the type of 5th wheel you have.
The ones like in the 1st photo shift more weight per hole than the ones in the 22nd and 3rd photo, just like on a trailer. The ones with wide spaced holes will shift more weight than trailers with smaller closer holes.

Huh?????
Sliding a 5th wheel to the front of the truck will transfer weight off the drive axles and place it onto the steer tires. Sliding the 5th wheel to the rear of the truck will take weight off the steers and add it to the drives.
Answer:
It does NOT transfer enough off the drives to make a difference. Been there, done that!
Think about it!
You can move your 5th wheel only so much. Usually, each notch is what..3"?
You STILL have the weight in the front of the trailer.....therefore, directly over the drive axles.
Slide the 5th wheel foreward, add weight to the steers.
Slide the 5th wheel backwards, remove weight from the steers.
Slide tandems foreward, remove weight from the drives.
Slide tandems backwards, add weight to the drives.

Answer:
Yeah, it's a (air) sliding 5th wheel switch. Used for putting more weight on the steers or for a better ride. When using ,most are a pain because they don't get used much. To slide, put the switch to unlock and check to see if pins withdrew from their locking holes. If not ,lock the trailer down and rock tractor until pins withdraw. If that doesn't work roll landing gear down enough to take weight off 5th wheel and try rocking some more. If that doesn't work, drop trailer and you may have to do a little hand banging with a hammer/ tire iron.
I have encountered a stuck one and driven down the road a mile or two with the switch on unlock so the bumps and road vibration would unglue the pins. Not recommended for rookies.
The air line to the 5th wheel is a dead giveaway. Now whether it works right is another thing.______
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I'd rather die on my feet like a man than live on my azz hiding in a truck.........Sir James Brown

Answer:
Right. You can not adjust a lot if weight, maybe 1000 lbs or so max if you are lucky, but sliding the 5th wheel still transfers weight between the drives and the steers.
I think of it as a fine tuning for those really heavy or poorly loaded loads when you need to move just a little bit one way or the other to get legal. Most of the weight adjustment is done on the trailer tandems which for the most part transfers weight between the trailer tandems and the drives.
Answer:
A properly installed fifth wheel, which is repositioned will transfer weight between the steers and the drives. How much can vary due to wheel base and increments on the fifthwheel. Sliding the trailer tandems will transfer weight between the trailer axles and the drive axles in a corresponding manner.
I will take that bet, Hoss, in any amount and at any time........Just let me know when you will be down here to pay off. ....
Lars; understands the use of tension to offset the effects of gravity.

Answer:
Ready to say uncle yet.
You do not remove any weight from the tractor as a whole, but you do remove weight from the drives when you slide the 5th wheel forwards to place it on the steers.
Answer:
OK Uturn, I buy the coffee the next time I get down your way.
Thanks Lars. Glad I didn't toss down a wad of cash on that bet.
My 5th wheel is welded in place by the guy that owned my truck before I got it. I've only had 2 instances that I should've slid it, but I was able to burn off enough fuel before I got to a scale.
Oh yeah..........."UNCLE!"

Answer:

OK, that's where I was getting my wires crossed.

Answer:
The 500# and 250# are rough guidelines, of course. The exact weight is dependent on several factors, like how the load in the trailer is distributed, your tractor wheelbase, and even tire pressures. It's entirely possible to be unable to scale a load legally when the gross weight is under 80k or even 70K; been there, done that, too.
And, sliding the fifth wheel can indeed shift weight to the trailer tandems; not all trailers are 53' long, remember, and again how the trailer is loaded is a factor
Answer:
Well Hoss we proved one thing here.
Two drivers can have a disagreement on something and not resort to infantile behavior.
Anyway you cut it, it was a good friendly debate.