Why box a frame?
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Laughing Gas
Joined: Oct 2006
Posts: 879
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From: Colorado Springs /Mesa AZ
Why box a frame?
I have have already read the threads on boxing a frame. Some just do the front to the firewall and others do it all. I am curious, what is the reason behind boxing these frames? I took a 351 out of a 79 Bronco and the frame was not boxed.
Posting Guru
Joined: Dec 2000
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From: San Diego CA
The frames in these old trucks was designed to flex as part of the deal. If you intend to leave your truck stock it'll be fine. If you intend to go faster, turn harder, stop quicker, or sit lower you need to box it to keep it from flexing. You wouldn't put a 500hp engine in a stock model T and and depend on the mechanical band brakes to slow it down would you?
I'll have the Roast Duck
Joined: Jul 2002
Posts: 9,622
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From: Northshore, MN
If you look at your bronco again, you'll see that the front crossmember is somewhat boxed, as well as the swiss cheese boxing from the crossmember past the motor perches. Which is my intention, to add the hollow oval boxing to add rigidity yet allow some flex and minimize cracking.
Cargo Master
Joined: Jan 2005
Posts: 2,497
Likes: 5
From: Tucson AZ
I like them boxed from front to back, IMHO boxing in sections just transfers stresses to the unboxed portions. The stiffer the better, let your suspension do all the moving and your frame won't have to. Spring 'em soft, shock em tight
Fleet Owner
Joined: Jul 2004
Posts: 27,299
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From: NM
Originally Posted by fatfenders56
I like them boxed from front to back, IMHO boxing in sections just transfers stresses to the unboxed portions. The stiffer the better, let your suspension do all the moving and your frame won't have to. Spring 'em soft, shock em tight
Post Fiend
Joined: Apr 2002
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From: Woodruff, SC
My intention is to box the whole frame that way in the rear i can shift the leaf springs inward and put a little wider tire under it.
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Posting Guru
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Post Fiend
Joined: Apr 2002
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From: Woodruff, SC
I'm still in the deciding stage on it. This is going to be a cruiser mainly, However i'm not ruling out a pass or two down the track to see how it does. I know inboard doesn't give me much handling capability, What about under the frame?....Too much sway? I've also thought about a 4 link.
Cargo Master
Joined: Jan 2005
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From: Tucson AZ
wiz, I went thru that same thing on this truck and decided to narrow the frame four inches and leave the springs on the outside, I got the fat tires without having to move the springs. You dont even have to cut the frame just bend it in right behind the front bed mount. Good luck
Posting Guru
Joined: Mar 2002
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From: Boise, Idaho
A little more about the design of the original frame...
It's true that the original frame is designed to allow flex, but it was not designed to bend. The design of the truck ties the front of the engine to the middle of the front crossmember, and the back of the engine is mounted via the bellhousing to both sides of the frame.
That forms a pretty rigid structure that prevents the frame from bending up or down, yet allows the frame to twist. This also puts the torque of the engine into the frame at a point where it's braced by the firewall.
Changing the engine to a modern side mount/transmission mount changes the entire dynamic. There is less structural resistance to bending, and the torque of the engine is applied to the frame at a point where it has no reinforcement to resist the twisting force.
There are bellhousings for y-block, FE's, 223's, flathead V8's, and the Lincoln y-block that have mounting ears. Chevy bellhousings from 1955 through 1957 had bellhousing mounts, too. Other than that, I don't know of other bellhousings with mounting ears.
Good luck.
That forms a pretty rigid structure that prevents the frame from bending up or down, yet allows the frame to twist. This also puts the torque of the engine into the frame at a point where it's braced by the firewall.
Changing the engine to a modern side mount/transmission mount changes the entire dynamic. There is less structural resistance to bending, and the torque of the engine is applied to the frame at a point where it has no reinforcement to resist the twisting force.
There are bellhousings for y-block, FE's, 223's, flathead V8's, and the Lincoln y-block that have mounting ears. Chevy bellhousings from 1955 through 1957 had bellhousing mounts, too. Other than that, I don't know of other bellhousings with mounting ears.
Good luck.
Post Fiend
Joined: Apr 2002
Posts: 5,964
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From: Woodruff, SC
Originally Posted by fatfenders56
wiz, I went thru that same thing on this truck and decided to narrow the frame four inches and leave the springs on the outside, I got the fat tires without having to move the springs. You dont even have to cut the frame just bend it in right behind the front bed mount. Good luck
