Built a crossmember for my 4 link front today...

Bryson said:
If I manage 20-25 steel fabricators every day I must know something. ;)
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Thats the same line we always get from "management".:roflmao:
 
vetteboy said:
This is what you'll run into eventually if you keep the axle brackets stock. The binding I mentioned is inevitable and something gives. The bushing deforms but you've still got that stress on the axle mount, and given time will fatigue at the welds. Remember...just because it flexes well, doesn't mean it ain't binding.

Reinforce the stock axle UCA mount, and the weak link moves elsewhere. Find the threads in the first few pages here about guys with radius arms that are eating bushings...that's the next step. Put all flex joints in and something else is gonna give...
Click to expand...

The UCA mount on the crossmember cracked not the diff. I am running a TNT truss with UCA mounts built into it on the diff. You are probably right about a little bind but isn't that why there are busings at one end and Jonny Joints at the other. I would think that it is nothing that they can't absorb. Anyway it has worked well for me.
 
squirrel80 said:
You are probably right about a little bind but isn't that why there are busings at one end and Jonny Joints at the other. I would think that it is nothing that they can't absorb.
Click to expand...

They absorb the deflection; the stress from binding is still present though.

Being that it was your crossmember mount that cracked, that shows the "weak link migration" even better. :)
 
squirrel80 said:
Here is the BDS crossmember I am running. It has worked great and the geometry works awsome. I have very good articulation and very little bind, but I do have a custom high steer and track bar location that puts the track bar at a very flat angle. I did recently have to gusset the upper control arm mount because it was starting to crack, but I have beaten this hard and it looks like it could have used it from the factory. Also BDS uses a side plate and crush sleeves for extra support, so they do not just rely on the bottom bolts.

DSC03832.jpg
Click to expand...

Why not send the upper control arm bracket back. Its guaranteed for life.
 
vetteboy said:
90% as strong? In what plane of bending?

In a situation where you land the rig on the crossmember, you are absolutely nowhere near 90% as strong. Now you've removed around 40% of the material cross-section at that point, and the majority of that is the section furthest from the neutral axis of the structural shape.

Keywords: area moment of inertia, and section modulus. Removing that part kills that section of tube as far as supporting bending stress in the middle. Being bolted on the ends will help though.

From the front, it's not nearly as big a deal. That's why so many truck frame weren't boxed from the factory. Given where you're applying the load I agree that the stress from the arms isn't going to be where your problem comes from.
Click to expand...

The plane of bending I was refering too was primarily torsional loading, and fore and aft loading under acceleration and braking. I agree with you that it isn't as strong as a whole tube in terms of a concentrated hit from the bottom. On the other hand, If you compare the vertical width, thicknesses, and bracing of the pictured BDS crossmember, my crossmember is still as strong if not stronger.

However, with all things considered it is still more than strong enough for what I'm after. I'm not really building a trailer'd rock killer here ;).
 
Looks great, but your still relying on those small bolts that thread into the bottom if the frame to hold up your drivetrain & hold your entire front end in place.
The croosmember looks strong, buy I would add some vertical brackets that bolt through the frame rails with crush sleeves.
 
barillms said:
Looks great, but your still relying on those small bolts that thread into the bottom if the frame to hold up your drivetrain & hold your entire front end in place.
The croosmember looks strong, buy I would add some vertical brackets that bolt through the frame rails with crush sleeves.
Click to expand...

I wouldn't really call them small. Each side has 4 5/8" grade 8 bolts... which equates to roughly 390,000lb shear strength when torqued correctly. I think it'll do just fine. :peace:
 
Bryson said:
I wouldn't really call them small. Each side has 4 5/8" grade 8 bolts... which equates to roughly 390,000lb shear strength when torqued correctly. I think it'll do just fine. :peace:
Click to expand...

Do you think you are going to get that full amount of strength only threading into a piece of sheetmetal?

After reading your build thread I think it will be fine for you, but it definitely isn't the strongest method.

Nice looking fabrication.
 
Dirk Pitt said:
Do you think you are going to get that full amount of strength only threading into a piece of sheetmetal?

After reading your build thread I think it will be fine for you, but it definitely isn't the strongest method.

Nice looking fabrication.
Click to expand...

The AVK's are inserted directly to my ruff-stuff stiffeners
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Thanks!
 
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