Truck bed install

[runaway parents]

Well I am gaining ground on truck bed remodel . if you all remember last fall I bought a slightly used (30year old)orchard flat bed. started to remodeling it. Til I got froze out and had to shut the job down for the winter . Don't have a big shop to work on this in.so it sits in the drive way.99.9999percent of the welding is done going to paint the areas I cant get to after the diamond plate is welded down.It is a ways out  but when I go to set it on the truck do I need to put a rubber pad between the truck frame and the bed frame?

[RandyA]

IMHO I see no advantage of using rubber between the bed and truck frame.  Rubber can compress and deteriorate which would make your bed less secure.  Your project sounds really neat.  I would enjoy seeing some pics or hopefully the real thing.

[Quickthrotl]

No need to isolate, I have done a lot of research as I am building a bed right now and all of the Big bed building guys do not isolate 

[rickeieio]

Hopefully a real engineer will come by, but for now, I'll chime in...

Isolation strips, wood, rubber, whatever, are to allow for some movement between the bed and the frame rails when the frame twists.  It WILL twist, and if the bed is fastened securely at front and rear, something is gonna give.  Think of a dump truck where the bed is only fastened at the rear.

That said, our relatively short frames and light loads don't promote much twisting. Our old '1949 KB-6 loaded with corn, coming out of the field though, is another matter.  It's oak strips were put on when the olde phartes built the bed in 1949.

[Quickthrotl]

I would respectfully disagree, as your bed will be bolted solid to your frame it will twist with the truck no matter what, your isolation material will twist with truck as well, all steel will twist and move. You walk a 12” I beam in a building when the framing is going up it moves way more than you would imagine. 

[noteven]

I would mount a body as per your truck manufacturer’s body builder manual. They and body builders have been at it for a while.

[ALLOY]

I've used both 3/8" convevor belting and 1" Fir (softwood) on flatbed decks.

The deck with belting was held on with Ubolts. Before tightening there was 1/8" gaps between the frame and deck.

The deck with Fir had more weld distorsion  (1/4"-3/8") and it was held on with Ubolts.

[GeorgiaHybrid]

On the later model KW trucks, you can download the body builder manual that is a very handy thing to have. Your truck should have something similar. KW recommends a rubber or plastic (Nylon or Delrin) spacer between the truck frame and the body as they will not undergo dimensional changes from humidity and they will prevent the two pieces from chaffing against each other. They don't have to be very thick though, just enough to do the job. They suggest using two clip angles, one on the body and the other on the frame and bolt between them for mounting.

Edit: They also recommend using a fish plate connection at the rear of the frame if you use U bolts to prevent reward movement of the body. If you download the 2017 KW T680 and T880 body builder manual from the net, take a look at pages 7-6, 7-7 and 7-8 for a description and illustration of those connections.

[Lance A Lott]

Keep in mind the factory body mounting instructions are for a body that will have tons of wheight on it not a 2000 lb car with a suspension of its own. A large comercial body or a box will be quite rigged its self and may not flex with the frame like our relatively light and flexible flat decks. I have Seen rubber wear steal more than steel on steel in some applications. Also are your going to drive your vehicle far enough for it to matter.  I have had several one tons with flat bed and none of them we're isolated. 

If you are making a removable deck this might be more important as it will probably have less rigid mounts for easy removal. 

[ARGO]

I used thin reinforced  rubber similar to mud flap material. My aim was to prevent the 2 pieces of metal rubbing each other bare & rusting between them, not expansion etc. My bed is side bolted thru the frame rail.

[Alie&Jim's Carrilite]

Even my old singled short 15 year old bed has wood spacers between it and the frame.  As far as the frame twist... My truck will rotate even being short.  If I'm on a hill, stopped for a light, when the light turns green and I run up thru the gears, the truck front of the  "Rears up" just like you see the heavy semi's moving away from a light.  That is frame twist.

[Lance A Lott]

Yes that is frame twist. I have seen both wood and rubber spacers used as well as no spacer. I have not found any ill agect from no spacer but i have seen worn bolts and elongated frame holes from trucks with spacers. In the rust belt salt and sand can get between the spacer and the steel and creat a grinding affect, if the body and the frame are bolted solid there is minimal movement. Both methods are used and on a rv hauler it probably wont mater at all. If you hat 60k of sand on the truck it might.

[NoDirectionHome]

As an engineer, I would recommend isolation material.  With that said, understand it is to allow an isolation of the bed/body from the frame to prevent damage.  The more important item is the area behind the cab.  That is your weakest point.  You should use bolts with springs to allow movement there with solid bolts at the back.

https://www.amazon.com/gp/product/B01CMJME46/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1

"No need to isolate, I have done a lot of research as I am building a bed right now and all of the Big bed building guys do not isolate"    lolol

[Quickthrotl]

11 hours ago, NoDirectionHome said:

 

"No need to isolate, I have done a lot of research as I am building a bed right now and all of the Big bed building guys do not isolate"    lolol

Appears everyone has a different opinion, Talking with Jack Mayer, he tells me that his company or Herrin does not isolate

 

 

 

[Quickthrotl]

i defiantly see no ill effect on doing it or not, I was stating earlier that it is not necessary 

[runaway parents]

Ok how about a Teflon  bar as an isolator?

[ALLOY]

With plastics some are made to keep things sliding like Delrin, Teflon, Polyethylene and Nylon swells in water.

 

 

 

[runaway parents]

Hmmm is there something a person can use that wont decay?

[Lance A Lott]

Reading this post got me curious to see how Freightliner hitched the body down on my school bus. It is 1 year old so is up to date. It has one of these brackets about every 3 feet. And the rubber pad on every cross member. I could not see any wear or rust. Some of the rubber pieces were screwed on and other were not.

My ton truck and my dump trailer have nothing for separation and i see no wear on those. 

[URL=https://i.imgur.coi*m/eywCKgw.jpg 

Looks like it will be an individual choice. I no right or wrong answer.

[Lance A Lott]

I had one more thought. If you were going to attach your deck with a plate bolted to the side of the frame then I think a isolation would not work very well. If your attachment method was a angles bracket on the side of the frame with a vertical bolt so that it creates a clamping affect or a u bolt  around the frame it would work well. 

[runaway parents]

I plan to reuse the stock angles that attaches the commercial fifth wheel on he truck frame. left them on the truck anticipating on bolting bed to them. should work ok. probably have to install  more forward and aft of that point because of the length of the bed.

 

[Lance A Lott]

This is what I am planing as well, I left them attached when I pulled the fifth wheel. I also pondered whether to put in a rubber pad. I have lots of 6" bailer belt if you need some its about 1/4" thick with a layer of thread. With your plan to use the existing angles it should clamp down very tight. At the moment I am leaning toward not putting anything in. The fifth wheel was bolted down tight after all and so is the body on my ton truck, also I will have a hitch on the back of the body so that portion will have to be very solid and that probably makes the rest a mute point. 

[Scrap]

Yea it may be a big ol semi truck but don't over-estimate it.  You take a single rail highway truck, load all your worldly possessions in the big sleepers, mount a high cg drom immediately behind the sleeper mount, side-load a car off the edge of the bed behind that, then load the rest of your possessions in a whole lot of toolboxes that need to open anywhere you may park, then counterbalance all that with a trailer another 10 feet down the line.  Then stop and beat your way into a parking spot every 250 miles.  It ain't easy being an RV truck. 

That said, if the body is being designed for a light application, then it needs to be marked somewhere on the door jamb or have a loading plaque installed somewhere conspicuous.  You don't need to re-rate the truck (unless first retail sale) but people are people and if it looks like a semi then someone somewhere is going to load it like a semi unless well marked.

Now most beds seem to have a subframe probably from experience and probably from needing to clear tires, but I'd assume you also want the thing to be torsionally stiff so it doesn't rip your car apart, leaves your tool box doors open-able anywhere you park, doesn't crack every corner on your body, etc.  So you tie it on flexible enough both so that doesn't happen and so you don't get a straight truck front end bounce.  But you still have to make it solid enough so you don't get the dump truck thunk as well.  That is why the KW manual above has flexible in the front and rigid in the back (BAM3).  The Europeans and COEs, however, don't like that and do the same thing with all flexible and frame spacer (BAM1).  Anything full rigid has a bunch of requirements and no frame spacer.  So there's many ways to skin the cat and frame spacer or not depends on how you do it.

Now add your Volvos (or is it just Mack's?) that have certain brackets/Xmembers with bodymount bolts and I don't know how you'd make a rigid mount by hand while reaming holes for those.  I'd guess you'd have to make it flexible just so you can deal with hand-built tolerances.  Or build the subframe & mounts on the truck first and then transfer to the bed.  Either way a frame spacer isn't going to be able to hold the tolerances for them.  They add a whole new dimension.

Anyways, long story short, the DAF manual is probably the best  out there in bodybuilder university.  Yes there is a lot to it and you have to read it a good 5 times over but all the decisions to space or not space and where to put all the mounts are in there.  It tells how to make the subframe as well.  CF and XF correspond to class 8 trucks.

http://www.dafbbi.com/~/media/files/bbi/bodybuilders-guidelines/en/bbg201222en.pdf  Start at page 51.

 

[runaway parents]

21 hours ago, Lance A Lott said:

This is what I am planing as well, I left them attached when I pulled the fifth wheel. I also pondered whether to put in a rubber pad. I have lots of 6" bailer belt if you need some its about 1/4" thick with a layer of thread. With your plan to use the existing angles it should clamp down very tight. At the moment I am leaning toward not putting anything in. The fifth wheel was bolted down tight after all and so is the body on my ton truck, also I will have a hitch on the back of the body so that portion will have to be very solid and that probably makes the rest a mute point. 

Sounds like we are on the same page. I also have the hitch built into the  bed probably wont mount bed on truck till this fall after camping season is over and the truck is parked for  the  winter bed is ready for paint and dimond plateing once this is done its vacation time!!! 

[DesertMiner]

Are you planing to install the hitch to the bed or directly to the frame?