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Attaching flatbed to frame rails


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i just placed 8" X8"X3/4" angle iron down on rails and used existing chassis  holes and drilled thru. Layed channel iron on crossways. Decking on top. Did put tube steel on outside of bed. Made neet clean strong outside. Simple. But the angle was laying around. Mine is lower than most but with my Freightsaker it doesn't go down as far as the Volvos. We need to know what truck you using. If you have all this figured out just disregrade my post

2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1

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I used the 5th wheel mounting holes, and put 3x3 ( I I think) angle next to the 6 inch channel I used to build the "frame" of my bed, then in the back back I used some channel mounted perpendicular to the frame and several 3/8s bolts



Edited by house
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I use springs to hold down my bed, don't have any good pictures, die springs with through bolts at each corner with locating tabs on the rails.  


2005 Peterbilt 387-112 Baby Cat 9 speed U-shift

1996/2016 remod Teton Royal Atlanta

1996 Kentucky 48 single drop stacker garage project

 catdiesellogo.jpg.e96e571c41096ef39b447f78b9c2027c.jpg Pulls like a train, sounds like a plane....faster than a Cheetah sniffin cocaine.   


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Here is a picture of the underside of the bed. It's being mounted onto a Freightliner FLD112.



The angle iron rails are for a 34.5" frame width. The freightliner frame is 33.5 If I simply cut the 2" angle off and weld 3" back on at the correct spacing, I can bolt it directly to the frame utilizing mostly existing holes. However, I don't know if HDT beds are typically bolted solid like that. If it's OK to bolt solid, how many places along the frame should there be bolts? 

Thanks to everyone who responded so far, I was hoping to get some pics of bed attachments before posting these specifics because there might be a totally different and better method of installing a bed.

house- it looks like your bed is bolted solid. Are there springs or other attachment methods at the front?

GlenWest- it sounds like yours is bolts solid also. 8" angle goes down the web quite a ways. I get that's what you had laying around, would you have been comfortable using smaller material; like 3"? How many places along the frame do you have bolts?

Edited by adhahn
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Don't remmember the amount. Lots of bolts. overkill. Every hole in rails got a bolt. Need to go down far enough to reach holes and have enough meat for bolts. You don't need that heavy a steel. You could use smaller steel and weld flat bar to it for tabs for bolting. Or some of the same angle iron. Lots of ways. Truck holes are for 5/8" bolts. I would use them instead of 3/4" and just use more. Have to ream out handened rails for 3/4". Not fun. lol. Have you been to the resource guide yet. Lots of truck beds on there

Edited by GlennWest

2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1

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Frames flex.  Don't try to make a rigid bed and attach it lots of places.  Something will give.

Newmar X-Aire, VATICAN
Lots of old motorcycles, Moto Guzzi Griso and Spyder F3 currently in the front row
Young enough to play in the dirt as a retired farmer.
contact me at rickeieio1@comcast.net

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 U-bolts are a standard method. Anytime one allows for the flex of the frame under the bed rails, it is also standard to put a soft medium between the frame and bed rails. Like rubber or wood boards.

 Do not drill holes into the frame flanges. (the top or bottom part) only drill new holes in the web. (the sides)

 If you use a heavy angle iron against the frame, use short pieces at the selected bolt holes rather than a full length piece. This allows for frame flex without shearing the bolts etc. Typically this scenario does not require a rubber or wood medium between the frame and bed.


I'm a work'n on it.

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My new bed is basically a copy of how my old bed, which is basically a cut down CM flatbed for a 450/4500, it is attached with 2 pieces of angle iron, 4 5/8 bolts through the factory hitch mount(2 on each side). then the factory trailer hitch has a couple of 3/8 bolts that go through the web of the trucks frame.  That bed has a B&W GN hitch welded in that I dropped about 6 inches to make the trailer ride level.  My trailer weights weights about 35K and I have hauled about 50,000 miles in the past 7 years and I check the bolts every year but none sheared off, at least so far.  


My new bed is much heavier as I used 8 inch channel for the main structure vs the 4 inch off my original, the same material I used to build my frame extension mainly because that is what I needed to clear the tires, I have not finished it yet but my last trip about 1200 miles the rear support was only attached with 4  #10 tek screws on each side, If those did not shear off during the trip I cant believe that 4 3/8 grade 8 bolts will. I guess I either have enough flex, or it is ridged enough to where it flexes as a unit.  my main concern when I built it was to add more rigidity to the section of frame I welded on to support the hitch, probably just my mind going wild but I just wanted to make sure that there was no way in heck that it could fail.


Edited by house
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Take a look for mounting recommendations:

Kenworth T470 Body Builder manual

Methods are generally the same for all manufacturers.

Rigid bodies like tanks are mounted with gusseted L brackets on the sills of the body and frame of the truck with a bolt and springs vertically that allows the truck frame to flex or rack under the body.

The body on my old truck is a pretty rigid welded steel affair. The original installer set the steel sills on the frame rails without isolation wood or whatever... when off road or crossing a steep approach (fuel station) the body squeaks and chirps and snaps and carries on...

I have “ install isolation strips” on The List...

"Are we there yet?" asked no motorcycle rider, ever. 


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  • 3 weeks later...

I used the angle iron that originally attached the 5th wheel to the truck.  Then there is a vertical plate on the back welded to the bed frame and bolted to the truck frame.  The vertical plate was positioned so that original fasteners could be removed and replaced with bolts.  My builder put 1" slats between the frame and bed, but they are very loose after 5 years.  If it were closer to the truck frame, I would glue so.e thin rubber to the frame.

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I set the bed down on the frame rails and blocked it up to where i wanted it. Got some 1/4 inch flat 2 1/2 inches wide. Measured how  long a piece I needed. Drilled holes in one end. Lined that up with factory frame holes. Bolted it in then welded it to the frame rail of the bed.  I used either 5/8 or 3/4 grade 5 bolts I don't remember. Each piece of flat was a little different. They are not spaced evenly either. I wanted to keep it simple and not have to drill a bunch of holes in the frame. I think I only had to drill out 2. There are 4 down each side. Probably should have used angle iron instead of flat. But I'm not hauling around a car either.

Farmer, Trucker, Equipment operator, Mechanic

Quando omni flunkus moritati-When all else fails, play dead
I'm a man, but I can change, if I have to, I guess.


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