I am still in the planning stages (have truck (53) but have not started yet.) I see alot of talk about boxing the frame. Are these truck frames weak for a streetrod? (no heavy hauling) I can see it on some older cars with weak or wood reinforced frames but do our trucks need them? I certainly understand on boxing when you alter the frame in a way that weakens it like when you c the frame so you can spring under the rear axle.

 

Gary, the main reason people box the frame is to stiffen the frame and prevent the frame from twisting. The old trucks didn't come with a sturdy frame and if you're planning on putting some serious horsepower in the engine compartment, I'd highly recommend boxing the frame. If your running a small block with average horses, you probably don't need to. It's a good idea if you plan on removing everything from the frame.

 

Gary -

The biggest reason folks box the frame is because they change the suspension to IFS and/or IRS. The independant suspension needs a stiff frame. Henry built these work trucks to flex...frame and all. If you stay with stock (or modified stock) suspension, there's no NEED to box the frame.

As Ed (imlowr2) said, average horsepower (<250 hp) won't require boxing either.

 

In the "old days" the frame was part of the suspension and was designed to be very flexible. Boxing the frame reduces the flex and twist and provides safe mounting for new suspension geometry.

 

I had an interesting conversation with Kent Fuller an old time California dragster chassis builder about this subject. Some of you may remember that Mike Bishop talked about him in the Jag IFS thread a while ago. Google search on Kent Fuller to get an idea of his backround. Kent when asked by me about the need to box the chassis for the IFS indicated that it wasn't necessary. I did not expect that response. I was talking to him specifically about the Jag IFS in my 49. He has personnally done a number of these installations in our Ford trucks in the past and knows the chassis. I intend to hook up with Kent hopefully in the spring and continue the conversation. My frame had experienced some minor butchery by a po to install a Buick nailhead so I want to box that area for those reasons, however I found Kents comment very interesting.

 

If anyone understands chassis flex it's Kent!

 

When me and a friend of mine carried the frame of my 51 out of the garage this weekend, it flexed. Alot. More than I would like to see. I could pick up ANY corner a good 4 to 5 inches off the jack stand before the rest of the frame started to move.

How can this be a good thing? If the frame is moving and twisting, with every little bump and expansion joint in the road, how can the suspension do it's job?

I'm going to google this kent guy and see what he has to say. IMO, the stiffer the better, both from a ride and handling point of view. If the frame is constantly moving, and the cab is bolted to the frame, wouldn't ride quality suffer everytime you hit a bump, the cab would move / flex with the frame, right?

I guess I have some reading to do.....

 

JK -

I'm not pretending to be an expert on frame flexing, but your frame sounds pretty funky. Have you checked all the connections to crossmembers? That much flex does seem a bit wierd. BTW, the cab is mounted so it will "roll" as the frame flexes.

Whenever you hit a bump, something has to "give" to absorb the shock. On a stock frame/suspension, the leaf springs and the frame twisting work together to do that. And it is surprising how much rough terrain these old trucks will take in stride. On an IFS setup, the frame is rigid and the springs absorb the shock. At least, that's the theory.

Where do you think the phrase "rides like a truck" came from?

 

Great thread, I was wondering whether to box my frame this spring. Since I'm staying with the stock suspension, it sounds like its not necessary.

 

I don't think that you will find in writing something by Kent or Mike Bishop aka av8ford that backs up what Kent told me. In fact if you search on the forum under av8ford and jaguar you will come up witha post by Mike that discusses Kent building a new box steel frame for one of our year ford trucks. That is why I was so surprised at Kent's statement to me. Just a guess that welding in the jag front crossmembef which is like a beefy K member may have been sufficint in his view. I certianly got the impression that he had done a number of jag transplants into 48-56 ford trucks without boxing. I do plan to follow up with him in person in the future.
As I indicated in an earlier post, I plan to box for another reason plus I am going to soft mount the jag complete crossmember like jag originally did.

 

Test post. I seem to be experiencing technical difficulties. Lost 2 attempted posts

 

I don't think that you will find anything in writing by either Kent Fuller or Mike Bishop that backs up what Kent told me in conversation. I may be getting old but that was crystal clear. In fact Mike Bishop in a post on the big jag thread talked about Kent building a new tube chassis with jag suspension. I am just guessing here that Kent may have welded in the jag crossmember which is a very stiff K member which should do a lot to stiffen the front of the frame.I plan to box for my other reason as stated above and I am going to soft mount the jag crossmember as was originally done by jag.
I still plan to follow up in the future with Kent Fuller regardless. lol

 

Actually the cab is NOT bolted to the frame, at least not directly. It is soft mounted so it does not twist with the frame. Ford was smart when he designed these frames. Up until probably the 80s, pickups were a work vehicle meant to carry full loads over rought terrain, NOT for giving luxury car ride and sportscar handling at 70 MPH jaunts down the interstate. For those less than 50 years old: country roads were not always covered with asphalt or concrete, in fact if you lived on a graveled street rather than a dirt path with grass growing between the wheel tracks you were considered to be in the CITY! Think what would happen to a rigid chassis as you drove it across a farm field with a full load in the bed as one wheel dropped into a rut and another rode up over a berm at 15 or 20 MPH. No standard suspension could deal with that much travel without bottoming out at least some of the time. At that point the frame must bear the weight and twisting forces, which on a rigid frame would likely permanently bend it and/or the sheetmetal attached to it. That understanding of utilitarian design is a good part of the reason why so many of our trucks survived the last 50-60 years for us to enjoy today.

 

I agree with Ax - watch a 18 wheeler as he powers away from a stop - the thrust of the engine darn near lifts one front wheel off the ground. Not really, but you can see the frame flex.

Every big truck I have ever driven has done this. The same is true with our smaller trucks - watch one bounce across some corn rows. They were built to flex and absorb jolts.

We used to run 6 and 8 ply tires aired up to 50 pounds and better - of course we now have flexible sidewall radal tires designed not to transmit jolts to the suspension - which can cause problems when we put new tires on the old trucks.

 

Great conversation guys thanks for the insite on why these frames are built the way they are

Rod