Diff housing stiffening and truss design

Root Moose

NAXJA Forum User
Location
ON, Canada
This is turd polishing of the first order since I'm doing this to a HP Dana 30 but this could be applied to any axle you'd want to truss.

The truss is to be welded across the top of the axle between the UCAs. I started cutting out some cardboard templates and got to thinking...

Instead of using an I beam type shape maybe it should be an inverted U shape out of a section of 2x4 box tube.

truss_x_section.png

Once upon a time I knew about second area moments and such. I could go look that stuff up I suppose...

If the I beam in A is composed of 3/8" peices welded together while the beam in B is 1/4" u channel I think the larger moment area is on A because of the thicker top flange. But it isn't a large difference.

Is this correct?

B would be better in resisting bending in the fore<->aft orientation for certain, right?

I think B would be a PITA to cut/fit but not terrible. I'd have to make sure the part that is welded to the axle tube has lots of a gaps in it to keep it from filling with water/mud/slush and rusting the tube from the inside of the truss. If I offset the gaps from the front side to back side then I could weld both sides of where the beam attaches to the tube.

The I beam style has nothing like this to be worried about.

Which would you do?

Also, the D30 diff housing itself is supposedly quite flexible and this is one of the big causes of gear failures (or so I've read/heard).

I was thinking that since the top of the housing is trussed this would minimize the flex in the cast section a fair amount. Especially if the U shape in option B above was used.

For the bottom it might be possible to sort of replicate this U shape profile by cutting a tube such that it is ~45 degrees relative to the ground but cut/shaped to match the diff housing. Let's see what rudimentary Photoshop skills will display:

truss_bottom.png

Is this worth the effort? Will it stiffen the housing appreciably? Will it be too much of a rock catcher? I'm not in the south west but we do have the occasional rock in the bottom of the boulder holes up here.
 
While the I shape will probably resist bending pretty well , although if you fliped a piece of angle iron upside down for a inverted triangle, it might be better. Just connect the truss to the upper part of the diff and it should be enough.

Actually with the gears if you set them a bit deeper it will help, then under load and when they "flex" the pattern will be correct. If you run a correct pattren while not under load then when load the teeth run to the outer edge and bad things start to happen.
 
IMNSHO, A would be the preferred choice. Both cross sections will provide the strength you are looking for, but A wins due to construction and finish concerns. I would replace the flat stock on the top cap with tubing in round,square or preferrably rectangular section. A offers no restriction in welding access, allows for painting on all surfaces and will be less of a catch-all for mud and moisture as you pointed out. 3/16" should be plenty strong as the strength is in the shape. Follow Rick's example and run you truss as far outboard as possible, ie. span as much of the axle width as you can.
 
As a refresher, here's what a "bare" high pinion Dana 30 looks like in primer:


Here is what I've decided to do:




There will be three ~2" diameter holes drilled in the largest vertical web of the truss. It is more for bling than anything else; it's not a huge weight saving and on a 4x4 I'm not convinced that unsprung weight is necessarily something to worry about.

The top of the "T" was kept fairly low to make it easier to service the UCA bushings. I was going to plate the open face of the passenger side UCA with 1/8" steel but after having just received LCA skids from JKS (1/4" plate) I decided to stick with 1/4" for that too.

I'd appreciate any feedback on this. Tonight I'm going to cut these parts out and will probably weld them on tomorrow evening.
 
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Root Moose said:
As a refresher, here's what a "bare" high pinion Dana 30 looks like in primer:


Here is what I've decided to do:




There will be three ~2" diameter holes drilled in the largest vertical web of the truss. It is more for bling than anything else; it's not a huge weight saving and on a 4x4 I'm not convinced that unsprung weight is necessarily something to worry about.

The top of the "T" was kept fairly low to make it easier to service the UCA bushings. I was going to plate the open face of the passenger side UCA with 1/8" steel but after having just received LCA skids from JKS (1/4" plate) I decided to stick with 1/4" for that too.

I'd appreciate any feedback on this. Tonight I'm going to cut these parts out and will probably weld them on tomorrow evening.

I can't really tell from your mockup (which looks sweet BTW), are you continuing the truss inside the pass side UCA mount?
 
take the pass side upper CA mount off and make one continious piece from the diff to the bucket then weld on whatever you need for the ca mount i beleive someone makes a machined piece to accept the bushing. the stock ca mount is extreemly flimsy and not worth keeping if you already going thru this much work.
 
Thanks for the input, guys.

I didn't run the "top" through the UCA. Didn't occur to me at the time. I'll look at it once I get in the garage today but "spidey-sense" is telling me it would be a PITA to get the welder in there...or maybe not...we'll see. Between the truss and the plating the UCA it may be overkill...but I think I'll try it.

The UCA will probably be plenty stiff once it is boxed. I boxed it more to reduce deflection (road feel) than for ultimate strength so we'll see how that works out.
 
bj-666 said:
take the pass side upper CA mount off and make one continious piece from the diff to the bucket then weld on whatever you need for the ca mount i beleive someone makes a machined piece to accept the bushing. the stock ca mount is extreemly flimsy and not worth keeping if you already going thru this much work.
X3.12!
It is a POS.
Make a solid one that will not warp or twist.
 
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