I'm thinking of stepping up to a FL sportchassis or equivalent to pull my 27 ft 5th wheel and boat. From reading some of the discussions it sounds as if everyone is using some type of air bag hitch on these trucks. Is this really nessasary when the truck is already gonna have air bag suspension, air ride cab and seats?

I'd say that yes, an air bag hitch is a necessity! I just got my first MDT with an air rear axel and a Mountain Master Air Ride Hitch, and did my first test tow and got the rig weighed. Empty the rear air bags need to support 5760 lb, and without an air bag hitch the 3000 lb pin weight would be supported by air bags with a pressure that's high enough to support a total weight of 8760 lb.

With the air bag hitch, I adjust its regulator so the hitch air bag runs at just enough pressure to support the 3000 lb pin weight. This is done by adjusting he regulator until I see about a 1/4" gap between the rear of the hitch base and the hitch frame. This gives a much softer ride for the trailer, that I guess is something like (3000/8760) = 34% the stiffness or spring rate compared to running with a plain frame mounted hitch without a separate hitch air bag.

The suspension on the MDT is pretty stiff and could fatigue the king pin on your 27 footer. I have seen pictures of king pins separating from the fiver due to the stress of towing by a heavy truck without an air hitch. In fact Teton Homes Fivers owners manuals model years 2003 & 2004 I know of for sure state under
II-E Items Not Covered by Limited Warranties Misuse and/or Abuse
#9 Undue stress caused by over suspension of the tow vehicle (gross rear axle weight rating in excess of 12,000 lbs must be softened with an air ride hitch and/or air ride suspension rated at no more than 12,000lbs)

Yes for two reasons

1) Air bag suspensions are not for a soft ride. They are for a level ride.

Now when the trailer is off, the air bags will have a lower spring rate than leaf springs giving a softer ride.

But when the trailer is on, the spring rate of air bags and leaf springs should be about the same.

2) In the beginning with pickup trucks pulling a 5th wheel, the trailer usually out weighed the truck by a significant amount. On a bump, the trailer would push the truck around.

As you get into MDT/HDT trucks, the mass of the truck is closer to the mass of the trailer. Now on a bump, there is a lot of energy between the two and your gooseneck frame takes the brunt of it.

That is why you need cushioning between the trailer and the truck, to extend the life of your trailer frame.

Why an Air Hitch

Topwater, as JM said the air ride hitch will help a lot with the forces on the trailer. You may not notice a lot of ride difference with the mass of the truck versus the mass of the trailer but it will help with the trailer fatigue.

I was the Vice President of the company that makes the TrailerSaver (since June 2005) for 10 years so I know a little about that specific hitch if you have any questions.

When we first bought the Volvo we were towing a 25' Terry fiver and it became obvious after the first couple of trips that the fiver was riding really hard; things were being thrown around inside that never occurred towing with the Dodge.

After we installed the Trailer Saver hitch there was a noticable improvement.

Thanx guys. Dennis once you installed the trailer hitch was it comparable to your dodge?
Looks like I'd need the receiver hitch version aswell so as not to pound the crap out of the boat when pulling it buy itself.

You can check out the TrailerSaver at the Tampa show next week if you're in the neighborhood. Or just call the company that manufactures them (Hensley) at 800-410-6580 if you have any questions. Aaron here probably knows more about that hitch than anyone in the world. I think he even has a TrailerSaver tattoo where no one can see it.

Sean, any benefit to having both the Trailer Saver air hitch and a Trailair pin-box? I've heard that it is overkill, but is there any specific reason not to use them both?

Roy

Your 2500 Duramax (3/4 ton) is a class 2 vehicle (10,000 GVW). Sportchassis MDT will be at least class 6 vehicle (26,000 GVW). Those "airbags" are not soft, they are designed to carry 26,000 GVW. That why some manufacturers will not honor their frame warranty if you pull with an MDT "without" an air hitch.
Why, they don't like to fix THIS.


hjs

Using an air pin is always tricky since it can move the pin location and add stresses the fiver wasn't designed to deal with. If the fiver manufacturer tells you in writing that it is fine and they will cover any problems then it isn't an issue.

Using an air pin and air hitch together is a hit and miss thing since you have two different sprung systems both with different spring and damping rates connected together. It could work great or it could toss your fiver around from a bad resonance in the system, no way to guess ahead of time which it will be.

Bottom line for me is that an air hitch is kinder to your fiver frame and that makes the fiver kinder to your contents that take less of a beating. Our first one (single acting) also gave a minor ride improvement to the truck. Our second one (double acting) was a huge ride improvement for the truck and even more for the trailer since it stopped the up-down impacts and cushioned the fore-aft shocks as well.

So, Stan, you're recommending an air hitch rather than an air pin box, right?

Roy

I wouldn't recommend air pin boxes except on the lightest trailers, for several reasons.
They don't have the capacity (because of the limit on the size of the airbag they can stick in there) to go much beyond the light pin load only. Remember, the limit on all airbags is 100 psi, but they also start acting like solid rubber beyond 75-80 psi.
They put additional stress on the pinbox in the wrong way.
You bust the pinbox welding, you're on your own, unless like Stan said, you got permission from the manufacturer to install it.
On big trailers with a 4-5,000 lbs pin load, they don't do a thing except stress the frame.
Advantages. The are cheap and I don't mean it in a negative way, from what I've seen they are well built.
So if you have a lightweight, cheap ("inexpensive") fifth go for it.
Using two of them, air pin box and air hitch, is not a good thing, unless you are a suspension, spring, etc., etc. "expert". The resonance Stan is talking about, you want to avoid it. Unless you do a lot of testing, you never know where the two suspensions might "find resonance" and actually multiply the forces on the fifth and the truck.

hjs

Interesting.......Teton Homes installs Trail Air pin boxes on most of their fivers. I wonder what their experience with them is?

Roy

This message has been edited. Last edited by: HighwayRanger,

Teton offers the Trailair pin box as an option. Couldn't find a cost or what modifications they made when adding it, if any on their site.

If you look at the design of the Trailair shown on their home page you will see that it moves the pin location forward quite a bit from the location it would be in with a normal fixed pin box. Interestingly enough buried in the FAQ is a mention that that is an older model and some newer ones do not extend the pin or do but only about 5 inches.

www.trailair.com

It does look like some of their designs use a larger diameter air bag but without reading a bunch of PDFs I couldn't find anything on carrying capacity or air pressure versus pin weight. I did find that they only offer about an inch up and down movement for a total of two inches of movement, that isn't much before you bang it into the stops.

Air hitches do cost more but if I was buying another truck-fiver combination they would be my first choice.