The Stovebolt Site Forums The Shop Area The HiPo Shop Boxing a 1-ton frame

I'm thinking boxing the frame on my 1-ton trailer puller project might solve some of the problems I've been wrestling with.

In short, boxing the frame will stiffen the frame a great deal, making up at least in part for removing the bell housing crossmember. That allows me to install my Cadillac 500 and Turbo 400 low enough to clear the cab while keeping my straight axle front suspension.

What do you think? Is boxing the frame going to allow me to remove that crossmember? I'm imagining I'll be adding a transmission crossmember back about 20 inches from the original location and maybe even add some diagonal supports forward to the spring hanger area.

This is the next installment in a series of threads I've started around this project, so I thought I'd list those just in case anyone wanted more background before telling me I'm nuts...

IFS Swaps that are on the road?

Making a Cadillac 500 fit in a '54 GMC

Hot Rod Tow Rig

Boxing the frame was an epiphany I had just minutes ago, so I'm headed out to the shop now to measure and think hoping to find some good questions and suggestions when I come back in... Thanks!

I don't think boxing a frame is such a good idea in this case.

It complicates the instillation of lots of other parts, wiring, brake lines, trailer hitch, anything that was bolted to the frame is now harder to do. You could cut large oval or round holes in your boxing plates to allow some access, but still a lot of work for some added complication.

I'm concerned that you will be removing the transmission crossmember which does a great job of tyeing the frame together at the rear of the front springs. To remove this would add some stress on the rivets holding the front crossmember in, as well as allowing the frame to try and twist and possibly spread at the rear of the front springs. Adding a crossmember a ways back will help some, but I don't see how boxing the frame will help as much as a properly placed crossmember.

Take a look at my solution to the same problem.
http://rides.webshots.com/photo/2236622090080251109tywgjR
I removed the transmission crossmember. Then fabricated two short sections of channel to "box" the frame for about 10" or so. The channel is bolted through the frame top and bottom with the spring hanger holes, new motor mount holes, and some extras as needed. Finally a new U shaped crossmember is installed in essentially the stock location to tie the frame back together and be low enough to clear the engine and transmission.

Something to think about,
Grigg

I see nothing wrong with boxing the frame as a rectangle is significantly stiffer than a "c" shape. You will need to X-brace where the original Trans crossmember was to keep the front suspension rear spring perches happy.

A doubling fish plate is a good idea where the new crossmember will be added.

Thanks for the replies guys, getting more brains involved is what I love about bringing ideas here.

I agree boxing the frame could add some complications and holes in the plates would help. I also think welding some nuts inside the frame would be part of the answer.

After looking the frame and visualizing it boxed I see the boxing as starting with the front crossmember and extending back to the third crossmember (the one under the back of the cab). That is about seven feet of boxing adding strength and stiffness through the area where the motor sets.

I'm somewhat relunctant to hang something real low below the frame between the axles. The transmission crossmember to support the Cadillac Turbo 400 will hang down a bit, but not as far as anything that could clear the torque converter.

The stock bellhousing crossmember is completely behind the center of the rear spring perch but only by an inch or two. A crude estimate is that the correct location of the crossmember to support the TH400 will be about 30 inches behind that same location.

I picture the new transmission crossmember fully below the frame, probably bolted to the bottom of the frame rail. Then a couple of diagonal supports going forward to the area of spring perches.

I'm liking this idea, but would rather hear other views and suggestions before I commit myself...

Thanks!

I can't help but think of all of the semi-trucks that have c-channel frames that carry 80,000 lbs. Their frames are designed to flex to keep them from breaking. I can see why somebody building a hotrod would want to super stiff frame, but if you are building the truck to haul loads, I think some flex in the frame would be good.

Boxing is good and I recommend it. Diagonals, I would think are a must and don't forget the exhaust will need clearance.

The Seeming low U shaped crossmember I used is really not that low. And it does clear the SAE #2 flywheel housing (about 19.5" diameter) for scale it's a 14" clutch in there.

My front axle is 10" off the floor.
With the suspension completely bottomed out the oil pan is 10.5" off the floor, and the U shaped crossmember is 10" off the floor.
I figure it's good to have something lower than the oil pan, like the front axle and the crossmember directly behind the pan.
At ride hight the oil pan and crossmember will both raise about 2-3" from those measurements, making the front axle lowest by about the same.

If you want to look for one of those crossmembers they seem to be in about every medium duty Chevy truck from the 70's and 80's. I saw a bunch at a junk yard last weekend, we even removed one for future use in an AD 2 ton similar to mine. It does need to be narrowed a couple inches, but that's not difficult.

Also figure if your engine mounts will impose any extra loads on the frame where it is somewhat unsupported?

Grigg

The Cadillac engine mounts are pretty far forward. A bit more so than a Chevy V-8. I'm not aware of any commercial mount kits designed for this chassis and expect to be fabricating my own. The front mounts will be close to the front crossmember and I think close enough that it will be well supported at front.

The Caddy mounts with the two front side mounts and then just the transmission mount. That means the crossmember I'll be fabricating for that mount will be important and will need to be mounted solidly. I don't believe an open driveline should transfer any push to the transmission but it will twist pretty hard, so I'm thinking I'll build an open x-member from the (front) rear spring mount to the k-member and use that to support the transmission crossmember.

That coupled with boxing the frame should stiffen things pretty well. I'm wondering if maybe I don't need quite as much box and could maybe just box where I need to add mounts inside the frame. But then I'm more than doubling the horsepower and torque with that Cadillac and I do intend to pull a heavy trailer with this thing.

I do not intend to box the frame back of the k-member. I see no reason to do so, and it simplifies plumbing, wiring and mounting the hitch.

The open x-member should allow room for the exhaust to pass through.

That's my thinking as I've read responses and now begin to fade tonight. Please offer any critique and I'll keep expanding my description or changing my plan until I no longer hear any issues that concern me...

Thanks!

Steve, when boxing the frame and truncating the plates mid channel, make sure that you have stress transitions on the frame something like this [IMG]http://thumb7.webshots.net/t/65/765/0/84/48/2492084480101989507ptsgzj_th.jpg[/IMG]

If not, the frame will crack where the boxing plates end.

Thanks for the pic Scott. I wanted to see what your crossmember looked like but had never asked or gone looking.

One approach I've considered is tying the boxing into the crossmembers it runs between. I've not thought through stress transitions, though at the front I don't think it would turn out to be a problem.

As I drove home from work today I was thinking through the boxing process and what it might look like, and realized there might be another approach, borrowing from Grigg's suggestion above.

I have a complete 1-ton frame in pieces, which I was considering cutting up to form the box plates. But if instead of cut lengths of that frame to match up to the original frame I can form a box using bolts instead of welds. This is attractive to me in that it makes it easier to remove should I ever make that choice.

I'm picturing a couple of bolted in box sections mounting the front engine mounts for the Cadillac. The box section might only be 18 inches long, but would add strength front the front crossmember rearward behind the engine mount. This would be the area most stressed by the added motor mounts.

The rear boxing might be a little more complicated but I picture something similar, perhaps in two pieces (on each side). One piece would add strength around the spring perch where I'm removing a crossmember and the second would be in the area where I'm adding a crossmember and back far enough to support the rear of a crossbrace.

I have a pretty clear picture in my head, but nothing on this computer with which to draw that picture.

Joe, you could always order some 2.5 x 6" 3/16" wall tubing and start from scratch, putting both the original frame and the 1T frame in the weeds behind the house. Since you are intending on IFS, need a new trans cross member, the only thing left to mount would be running board brackets and rear leaf hangers.

Who is Joe and how did he hijack my thread?

I rejected building my own frame a year or so ago when scrap was running $300/ton. Jeff and I got $40/ton Saturday for a load of scrap, so maybe steel has come way down too?

The idea has some attraction but I'd rather start with something factory made, either with all the body mounting in place or the suspension mounting in place.

I'm not committed to IFS and go back and forth as to whether I want to do that. I'm tring to sort out all the issues before I get committed to some aspects. A solid frame strong enough for my application is my priority. Front suspension will follow from some of the other decisions.

Running IFS either means finding the right wheels or widening the fenders. I've considered widening the fenders and would probably lean that direction if it comes to doing IFS.

Sorry Steve,

My suggestions would be to take a few pieces of paper and write IFS on one, Solid Axle on the other, stock frame on the next and custom frame on the last. The put them in a bowl, shake and pull two out. Or do a KT chart and analyze it to death. http://web2.concordia.ca/Quality/tools/10decision.pdf

In lieu of widening the fenders, use big bolt fenders (they are already wider)

Just my two cents.

Scott I actually have a couple of documents where I'm tracking the issues and advantages. I'm not ready for a decision matrix because I don't feel I've got all the factors worked out yet...

When I get a little further along I might expose my worksheet and explain my weighting and decision.

Scott hit the nail on the head about the transition from box to channel. I've seen a lot of cracked frames right where a boxing plate ended that was square to the frame. The early for sure and maybe all S10's transition from box to channel somewhere near the back of the cab and the inside frame face, which is the same as a boxing plate, has a parabolic shaped end to gradually go from stiff to flexible. I haven't seen the 51 GMC with the 500 lately but do recall that the transmission crossmember is also a "K" member. It never hauls anything heavier than blueprints and never pulls a trailer so it probably isn't a good model for you.

The more I think about this a x-member makes sense to me. I might be able to take some messurements tomorrow and see if a big x can add the stiffness and also create the transmission crossmember. Boxing the frame, or at least parts of it, will be necessary to properly attach the x-member.

Or at least that is what I think tonight.