What is needed for the rear spring hanger (assuming it is bolted on the bottom to an L-bracket) is a beam running under it. The horizontal leg of the L-bracket will just bend if there is a crossmember inside the frame alongside it.

A frame rail that is boxed and 2" deep will be a little less than 2/3 the strength of a C-channel 4" deep. The stiffness of a channel goes up as the square of its depth. What you've done is pretty much the standard hot-rod modification, which I personally have an engineering issue with. Depending how how fore/aft you boxed, you may or may not have problems down the road.

Not trying to rain on your parade, but I hate to see suspension mods that could be dangerous. If you aren't going to carry loads, or drag race, or tow with it, I may be worried about nothing.

 

The boxing plate is 13 inches long and is 3/16ths. It will not be used to tow or haul anything heavy.

A regular spring hanger has an L bracket built into it and would put a moment about the frame rail the same as my L bracket. I am just hopeing my L bracket can handle the internal forces. Mine is further back from the crossmember so the frame would have take up some more twisting. Might as well move it back some.

The other bit of fun with the new springs is the rear portion of the spring is longer. The spring is 56 inches long and the axle is 24 inches from the front hanger. I beleive this makes 57% of the load go up front and 43% out back right? That should help me some with the c-notch and the twisting force put into the rear portion of the frame.

I appreciate the input, its been a few years since I took all those ME classes

 

ABQ, I hear where you're coming from. This is how I'd do it to retain frame strength:

 

I'd add a triangular gusset piece to the end of the angle iron to prevent the horizontal arm from flexing (see below).

I'd have to go back to physics that I haven't used in a long time to prove it, but my gut tells me that the longer rear moment arm of the spring and the fact the front section is stiffer and on a pivot that the majority of the stress and strain of the suspension movement is going to be on the rear hanger. It will see both up and down strain as well as twisting strain as one end or the other of the axle moves up and down independently. A full height crossmember at the hanger attachment would be very desirable IMHO.

 

I dunno I think the front takes the bigger brunt of the action, most leafs I have dealt with the front bushing is twice the size of the rear one.

 

Another option might be to use some doubler plates in conjunction with boxing the frame to spread some of the load back there. It's not the most structurally efficient or cosmetically appealing option, and you may not be able to get back all of the frame strength but I think you could get back a lot of it considering that the original frame isn't all that thick to begin with,

 

Didn't the drag racers use springs set up like that (more of the leafs towards the front) to help eliminate axle wrap on hard starts? It seems like I remember something about the MOPAR guys calling them Super Stock springs or something along those lines.

......I could be wrong here......

On my 49 I moved that rear x-member all the way to the rear (mainly to accomodate the fuel tank) I did add some additional x-members (again, mainly for fuel tank mounting) but they will definately provide some stability.

Bobby

 

yes the shorter front 1/2 the spring acted like traction bars since they were stiffer, the rear 1/2 did most of the flexing. The front bushings are thicker to absorb front to back shock like from hitting a pothole or RR track, that has nothing to do with up and down or twisting stresses. If the rear of the spring is doing most of the flexing it will also be stressing the rear hanger more. I personally prefer to err on the side of safety but it's your life...

 

Gary, I'm glad you recognize the issue and have the knowledge of the impacts of these changes! I think it's easy to lose sight of the design concepts ol' Henry had in mind when these old horses were built.

 

The fixed end of the spring transmits all of the HP from the engine, and all of the rear braking forces. The rear eye pivot can only react to vertical forces.

As far as reinforcement, Ax's sketch is the ideal; if you don't have the clearance to do that, you can add plates on the top and bottom flange. That gives the most strength per pound of metal added.

 

Ax I am sure you have forgotten more than I know

I agree that the rear will be flexing more, but its a longer lever arm so less force should be needed to keep it in place. The front of the leaf locates the axle more and like you say takes the hit more on bumps and what not.

Certainly safety is paramount but chances of the rear shackle bracket sheering is very low worst case scenario it would turn into a V and I would have some tweaked leafs.

The C-notch I see being a problem if I put a 1000 lb tongue load on a trailer hitch. Heck I probly improved my safety in case of a rear end collision, it might actually give me a bit of crumple zone

 

Gary,

My truck is stored for the winter so I can't get to it right now. As I remember the bumper brackets go in about 5-6 inches. You probably should have them loosely bolted on before you move the crossmember rearward. My 48 is an F-3 and I had to cut 12 inches of frame off the rear in the shortening process so my frame might not be the best thing to take measurements off of anyway...

 

Interesting discussion on springs here....

Thanks guys!
Bobby

 

Gary,
Having just c-notched my frame I highly recommend you need to reinforce the notch by adding depth as shown in Ax's diagram. I just welded in a section of the 2X2 crossmember, which I had removed from the frame, to the top of the frame. Since you have to bump up the bed for the rearend already this shouldn't be a problem.
Secondly, while the front spring perch takes most of the fore/aft loads, the rear takes the all vertical load of the rear of YOUR truck (deadload) not just the load you put in the bed (liveload). The combined dead and live loads will cause the rear frame to twist if not restrained and will fail over time. If my memory serves me right weren't there crossmembers very near both the front and rear spring mounts? I would suggest you move the rear crossmember back as close to the rear spring support as you can. I moved mine back to enable placement of the gas tank, where is your gas tank going to end up?

 

Here's how it lays out; assuming truck weight and fore/aft distribution, you can figure out the forces sitting still on each end of the spring. These forces will double or triple on the road due to bumps, railroad tracks, etc. This is because the axle and truck have to be accelerated upwards over a bump, and are brought back down by gravity very quickly.