RGN trailer front too low if loaded

[ichudov]

I have a semi truck and a 48 ft RGN trailer. Both have functioning air bags. Trailer is Trailking TK60MG with mechanical gooseneck.

The problem is that when the RGN trailer is loaded, the front of the bed is too low to the ground. Like just 4 inches off the ground.

My feeling on this is that something flexes and the neck bends in relation to the bed, and it "sags".

I wonder what is the proper way to address it. I thought to buy some steel wedges to insert when hooking up to the trailer, so that the overall sag is compensated.

Am I on the right track and does anyone have any suggestions. Thanks a lot.

 

[Junkyard]

Okie dokie here's whatcha do.....

What's your 5th wheel height? Anything under 48" is too low. Ideal is 50-51. That being said there are two places you can take up the slack in the neck. First is the pin and stirrup. I used to use old main bearing halves between the pin and stirrup. Also you can stick a piece of angle iron at the base of the neck where it touches the deck. These are installed before you back under the trailer while there is slack. You're seeing deflection in the deck and neck but the greatest loss in clearance is all the slack in the neck. Watch it as somebody backs under and see how much it moves before you start to lift the trailer. You'll be surprised. Another obvious way to see it is when you pull out from under it once the deck is on the ground watch how much farther the neck moves down before the truck is out from under it. Those two shim places will make a big difference. I bet you'll gain several inches easy.

That's the most common thing I see. Beyond that we need pics, where the load is on trailer etc.

 

[crane operator]

I guess you need to figure out if its really flex, or as junkyard mentioned, your truck is just too short. I had the short truck issue on a trailer.

My roll back trailer traveled too low on the front. We were close to catching landing gear.

I was out of adjustment on the tractor air bags (that's the easiest way to gain height), so I went to the junkyard and found a 5th wheel that was taller. I've also seen people put riser blocks between the 5th wheel and the frame rails, but I prefer a taller 5th wheel.

You can also go to taller rubber, but you may have to change rear ratios to compensate.

I think this is your new trailer, from one of your earlier posts, and I'd say you need to get your truck height up. Its hard to tell from a picture though, it may be just the ground making it look that way. Is it noticably low only on the very front?

If you want to just cheat a little and see what some tractor height would do, take your adjuster off the tractor bags, and air them up high while setting in a parking lot loaded, and take a good look at it height wise. Won't cost you anything.

Did you get a set of rails built for the tractor frame rails yet?

 

[Junkyard]

Neck sure looks a little negative to me in relation to the deck. 5th wheel is also pretty low too. That forklift all the way forward doesn't help .

 

[crane operator]

I've never seen the pin and stirrup trick, I'll file that one away. I've always just seen them shimmed at the back of the neck where it touches the trailer.

 

[Junkyard]

I've never seen the pin and stirrup trick, I'll file that one away. I've always just seen them shimmed at the back of the neck where it touches the trailer.

I'll let y'all have that one....no charge!

 

[RZucker]

I guess you need to figure out if its really flex, or as junkyard mentioned, your truck is just too short. I had the short truck issue on a trailer.

My roll back trailer traveled too low on the front. We were close to catching landing gear.

I was out of adjustment on the tractor air bags (that's the easiest way to gain height), so I went to the junkyard and found a 5th wheel that was taller. I've also seen people put riser blocks between the 5th wheel and the frame rails, but I prefer a taller 5th wheel.

You can also go to taller rubber, but you may have to change rear ratios to compensate.

I think this is your new trailer, from one of your earlier posts, and I'd say you need to get your truck height up. Its hard to tell from a picture though, it may be just the ground making it look that way. Is it noticably low only on the very front?

If you want to just cheat a little and see what some tractor height would do, take your adjuster off the tractor bags, and air them up high while setting in a parking lot loaded, and take a good look at it height wise. Won't cost you anything.

Did you get a set of rails built for the tractor frame rails yet?

And.... To the op, If you jack the air bags, check your u-joint angles before you drive it. I sold off an old Volvo a year back, (48" 5th wheel) the farmer that has it got a belly dump with pinned landing gear. Rather than blow a new hole in the legs, his driver jacked the bags and blew out the inter axle u-joints. Dip wanted me to warrantee that...???

 

[ichudov]

rane op, thanks for dredging up that picture, it shows the exact problem. The problem is very visible from the side, also, as the goose neck visibly sags downwards towards the trailer , which is NOT the case when the trailer is NOT loaded. It only shows up when it is heavily loaded.

Maybe I should make half circles from steel strips and insert them into the "shackles" prior to hooking up, when I plan to travel heavy.

Overall it looks more like something is flexing too much but I am not sure.

 

[crane operator]

And.... To the op, If you jack the air bags, check your u-joint angles before you drive it

I guess I wasn't suggesting to drive it around that way, don't drive with the bags all the way extended. I meant to just to look at it that way in the parking lot, to see if it gave him the height he needed. Then he can see about 5th wheel or taller tires. Thanks for clearing that up rzucker.

I've only been around mechanical necks loading and unloading guys, I've never owned one. But all the ones I've been around, all have shim plates made up, I've just seen them at the back of the neck, not like what junkyard recommended, but his would work too.

That said, the neck is still going to flex, the whole trailer does. You just need to get it to a decent travel height. I've got like a 1 1/2" tall shim on my hydraulic rgn, that I use when my 40 ton rt is loaded up. It travels fine empty with a much smaller or no shim at all. I usually just leave in the tall shim though and run around with it up high when empty.

 

[ichudov]

I heard some stark warnings that ride height on tractors should NEVER be adjusted and that there is only one correct ride height. I would rather not mess with that and address the neck issue.

 

[Junkyard]

I always used both when I had to shim a mechanical neck trailer. The single biggest change will be at the heel of the neck but sometimes that little extra at the pin helps.

 

[Junkyard]

I heard some stark warnings that ride height on tractors should NEVER be adjusted and that there is only one ride height. I would rather not mess with that and address the neck issue.

Hogwash. Can you get it too far one way or the other and have issues? Absolutely. The idea that there's one hard and fast spec for ride height is crazy. All the bouncing trucks do going down the road, improperly repaired leveling valves/linkage. I've had KW's with factory over-inflate on the suspension.

In this particular case it was merely a suggestion to see how much clearance you'd gain by raising the 5th wheel the same amount.

 

[Crummy]

I had the same problem with my TK70 & short rubber on the truck. I got a 10" slider, I think it was around $700 brand new. Problem solved & I kept the 7" which will go with the truck when I sell it if someone is pulling a van & needs to have the low plate height.

 

[Crummy]

 

[ichudov]

Crummy, looks like a nice ride height throughout. Did you use any shims on the neck?

 

[Crummy]

Crummy, looks like a nice ride height throughout. Did you use any shims on the neck?

No, just the higher plate height. Like @Junkyard said, 50-51" is what Trail King calls for.

 

[ichudov]

Thanks. Your trailer looks aLMOST exactly like mine.

 

[crane operator]

I took some pictures this afternoon when I was down at the shop

The first one is the old riser that was under my 5th wheel. The second shows the new 5th wheel. The truck has lopro 22.5 rubber, and air suspension. Its far cheaper to change 5th wheel, than buy tires ( go to 11r22.5), or rims and tires to go to tall 24.5, and then change 3rd members, to change rear ratio, to deal with the taller rubber.

I gained about 4" at the 5th wheel.

I think the big deal on the 48" height is for all the over the road guys swapping trailers at the freight docks, if everyone's running the same height, it saves a bunch of jacking loaded trailers.

You're just running your own trailer, so set it up how it works for you.

Maybe you can get by just shimming the trailer, but extra height makes a big difference crossing railroad tracks and speed bumps, and high centered intersections.

I would get your 5th wheel height figured out, if you need to change it, before you build your frame ramps.

 

[crane operator]

Before the 5th wheel change, I was barely clearing the landing gear feet, and the trailer deck was noticeably downhill. This picture is without the tractor bags aired up, but with air in the tractor, the trailer deck is now level.

 

[Metalman 55]

We made up these blocks to better height match our new to us lowboy trailer to the tractor that we had. I think they were 3" thick if I remember correctly. Took a while to drill through the 3" blocks though!