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Bed Build Planning


rickeieio
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So, today I got the ET hitch.  Now that I have it sitting next to the truck, I can easily measure and see why my ideas won't work.  And also see new possibilities.

The conventional way to mount the hitch seems to be to add enough to the frame rails so the hitch can be slid in as far as practical.  It seems that on a KW T-680, I could slide the hitch all the way to the rear shock towers, if there were not a pesky leveling valve in the way.  Try as I might, I can't find a way to move the valve and keep good geometry on the link rod.  Unless...what if I turned it 90 degrees and mount it to the front of the hitch, between the shock towers?  If this works, I can remove all the cross member bracketry in the back, and replace it with a plate tying the two hitch support angles, thus also eliminating the need to lengthen the frame a paltry 4 inches.

Tomorrow I put another set of eyes on it and see why it won't work.  I'll take pics too.

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Rick I'm pretty sure you can mount the levelling valve however you need to as long as the arm has travel clearance to deflate the suspension.  On the hitch frame could be fine. A new rod can be invented. Provide service access to it so it will never ever fail... 

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So, here's what I have to work with:

[https://i.imgur.com/KJKSnjml.jpg   

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The hitch is 34" long, so will extend 5" farther than the frame.  I'll need to drill a new mounting hole in the supplied angle on each side.

Edited by rickeieio
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Rick,

Shouldn't be a problem to rotate the valve 90 degrees and bolt it to the front frame on the hitch. The bottom plate on the hitch plus the hitch stiffening the bottom plate will more than make up for the removal of the two cross members. That plate acts like a diaphragm bracing plate.

if you locate everything Correctly, you might not need to even modify the rod.

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On 5/16/2021 at 3:02 PM, GeorgiaHybrid said:

if you locate everything Correctly, you might not need to even modify the rod.

Got everything else up to the shock towers removed today.  After much head scratching, I decided to fab up a simple bracket to relocate the valve independent of the hitch, just in case I might someday need to remove the hitch and still drive the truck.

I did heat the link rod and give it a 90 degree twist.  I really wanted to get it in place and a picture of it, but the paint wasn't dry.

Some preliminary measuring leads me to believe one hole on each side of the frame will be nearly perfect for the support angles.  Can I be so lucky?

Edited by rickeieio
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Rick,

I cantilevered my hitch 4" past the frame.  Still got all the bolts in the frame.  I added a 4x4 piece of steel angle and bolted that to the overhanging part of the hitch.  Welding would have been better but I don't weld, so bolts snugged the overhanging tail up and gave me extra piece of mind.  Don't have any photos handy but can snap/send some, if you want.

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There's always something that crops up that will case you to stop and wonder if you've done something wrong, of if someone else has......

Out with the cross member and ET is ready to go in.

UuVuf1Dl.jpg

But wait, the cross member is this wide:

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And the ET is this wide:

XOoJ2cJl.jpg

So it seems there's 3/4" gap between the frame rails and the hitch.  The holes in the hitch are very tight, no room for wiggle.  So after consulting our resident metals guy (GeorgiaHybrid) and calling PopUp hitches, I need to cut out two 3/8" plates roughly the same size as the support angle to shim it out.  Of course I have no 3/8" plate so I'll fetch some in the morning.

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8 hours ago, noteven said:

Rick - a KW will have 16mm frame bolts in 17mm holes to allow the frame to have the flexibilities. 

The frame is drilled on mm dimensions.

Yes, I've long wondered why truck manufacturers allow for this while the hitch builder made a point of making very precise holes so no movement.  But, I'm not an engineer.

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10 minutes ago, rickeieio said:

Yes, I've long wondered why truck manufacturers allow for this while the hitch builder made a point of making very precise holes so no movement.  But, I'm not an engineer.

 

8 hours ago, noteven said:

Rick - a KW will have 16mm frame bolts in 17mm holes to allow the frame to have the flexibilities. 

The frame is drilled on mm dimensions.

I wasn't clear Rick - the frame holes are laid out in mm on center, as well as being drilled in mm dimensions. 

If you want to extend your frame with a couple chunks to support the hitch the Kenworth Body Builder Manual on the KW website has the correct procedure for preparing the splice and welding.  It is 120,000psi heat treated material in whatever dimensions you measure.

You can sometimes find frame pieces at up fitters - customers often buy a stock straight trucks and the up fitter cuts off frame to suit the body. 

Those 3 piece cross members are appreciated if you have to change one where you can't just slide it out the back... but they aren't "the cheapest" way to build :)

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Understood.  I don't need to extend the frame.  The hitch will stick out the back by 4", so I will need to relocate the rear most hole.

Now I need to decide whether to rent a mag drill.  DW pointed out that drilling a bunch of 3/4" holes is hard work, in difficult positions.  $60 to rent the drill v. a couple visits to the chiropractor.........

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If it is like my Milwaukee mag drill it will weigh about 70 pounds.      I use my crane to position the drill, if you have an engine hoist USE IT.    My drill has a 3/4" Jacobs chuck, it will hold annular cutters.     They are kind fragile, I use hole saws for most holes.      I spot the holes with a 1/8~1/4 drill deep enough to register the pilot or bigger drill.      5/8 holes are at the min size range for either hole saw or annular cutter, a good cobalt twist drill is just fine for frame rails.  

Steve  

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