Question for the fabricators amongst us

mrblaine

mrblaine

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Do you trust what you know? Can you look at something done a certain way and derive anything useful from how it is done?

Or, do you just throw lots of metal at it and solve the problem that way?

Hypothetical case in point-

Transmission cross member to hold up a 32RH at the end of a 4.0 with a NV241OR hanging off the other end.

What size would you make the cross member?
What size would you make the bushings if you use them at the frame?
Would you try to reuse the OEM trans mount?
What thickness would you make the tabs for the frame side connections?
What diameter and grade bolt through those tabs?

Do you trust what you know?

Bonus question- can you make the 97-02 transmission adapter mount low profile, if so, by how much?
 
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Fouledplugs said:
Not a fabricator yet, but I like how this forces me to dig deep and learn how to approach details that matter when modifying/fabricating something.
Click to expand...
How thick are the axle side lower control arm mounts?
How often do they fail when NOT subjected to crash forces?
How much torque can the OEM trans mount deliver to a secondary cross member?
How much weight is the cross member supporting?
How thick are the OEM control arms?
Why don't they fail more often?
 
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mrblaine said:
Do you trust what you know? Can you look at something done a certain way and derive anything useful from how it is done?

Or, do you just throw lots of metal at it and solve the problem that way?

Hypothetical case in point-

Transmission cross member to hold up a 32RH at the end of a 4.0 with a NV241OR hanging off the other end.

What size would you make the cross member?
What size would you make the bushings if you use them at the frame?
Would you try to reuse the OEM trans mount?
What thickness would you make the tabs for the frame side connections?
What diameter and grade bolt through those tabs?

Do you trust what you know?

Bonus question- can you make the 97-02 transmission adapter mount low profile, if so, by how much?
Click to expand...
Funny you bring this up as I am looking to do this over the winter and in researching came across this thread https://wranglertjforum.com/threads...on-cross-member-and-transfer-case-skid.34524/ I think material wise it looks probably a little beefier than what is truly necessary but the materials used are something common and readily available to most so that is something to consider as well. My only question about this style of crossmember is the bushing location. It seems to me that it should be closer to the transmission centerline but I am probably missing something. I know when I do this for the four popper that I have to make sure to have as much dampening possible to keep the fillings in place. So I am going to attempt to add something between the crossmember and the mount.
 
Were we seriously thinking of the same thing at the same time? The email was sent 2 minutes before you posted this!
 
Last edited:
mrblaine said:
Do you trust what you know? Can you look at something done a certain way and derive anything useful from how it is done?

Or, do you just throw lots of metal at it and solve the problem that way?

Hypothetical case in point-

Transmission cross member to hold up a 32RH at the end of a 4.0 with a NV241OR hanging off the other end.

What size would you make the cross member?
What size would you make the bushings if you use them at the frame?
Would you try to reuse the OEM trans mount?
What thickness would you make the tabs for the frame side connections?
What diameter and grade bolt through those tabs?

Do you trust what you know?

Bonus question- can you make the 97-02 transmission adapter mount low profile, if so, by how much?
Click to expand...
I would not reuse the OEM mount. I would use 10 gauge or 3/16ths - whatever I had on hand in that range for the tabs. I would use a bushing with similar properties to whatever engine mount is being used so they don’t fight. If needed for deflection resistance I would weld in 1/8th to tie the tabs together above the bushing. Grade 5 is plenty for hardware.
 
Blackjack said:
Funny you bring this up as I am looking to do this over the winter and in researching came across this thread https://wranglertjforum.com/threads...on-cross-member-and-transfer-case-skid.34524/ I think material wise it looks probably a little beefier than what is truly necessary but the materials used are something common and readily available to most so that is something to consider as well. My only question about this style of crossmember is the bushing location. It seems to me that it should be closer to the transmission centerline but I am probably missing something. I know when I do this for the four popper that I have to make sure to have as much dampening possible to keep the fillings in place. So I am going to attempt to add something between the crossmember and the mount.
Click to expand...
Bushing location is odd when it comes to predicting how that will react to vibe reduction. I do extra to keep the vibes down and even more oddly, I've found that the smaller versions from Autofab work better than the larger ones do. Not quite sure why though.
 
BuildBreakRepeat said:
I would not reuse the OEM mount. I would use 10 gauge or 3/16ths - whatever I had on hand in that range for the tabs. I would use a bushing with similar properties to whatever engine mount is being used so they don’t fight. If needed for deflection resistance I would weld in 1/8th to tie the tabs together above the bushing. Grade 5 is plenty for hardware.
Click to expand...
How thick is the factory axle side lower control arm mount?
 
If Artec made power poles it'd probably look like this one I saw a few years ago:

IMG_20170823_104937.jpg


IMG_20170823_104236.jpg
 
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mrblaine said:
Roughly 1/8" maybe just a tad more. Point being it is nowhere near 3/16" so if that thickness will handle hitting a pot hole on the freeway at 60+ mph, why won't 1/8" hold up a transmission?
Click to expand...
Radius bends decrease deflection by a significant amount. That wasn’t part of how I would approach it because I wouldn’t care for the extra work.
 
BuildBreakRepeat said:
Radius bends decrease deflection by a significant amount.
Click to expand...
Look at the unsupported height inside the mount up to the top of it. The bolt and bolt sleeve in the bushing provide the other two sides of the box and you can cut the radius bends completely off below the bushing with little effect on the strength. That is at least a couple inches of unsupported side up to the top of the mount so if that can handle the lower control arm, why won't 1/8" work for frame tabs with an unsupported distance of sub 1"?
 
mrblaine said:
Look at the unsupported height inside the mount up to the top of it. The bolt and bolt sleeve in the bushing provide the other two sides of the box and you can cut the radius bends completely off below the bushing with little effect on the strength. That is at least a couple inches of unsupported side up to the top of the mount so if that can handle the lower control arm, why won't 1/8" work for frame tabs with an unsupported distance of sub 1"?
Click to expand...
Oh it absolutely will work. I have no doubt. In reality the strength comparison of 0.015625 is really inconsequential. What idiot is trying to say that 1/8 isn’t enough?
 
mrblaine said:
So in other words, I can trust what I know? Why does it need to be boxed, or does it?
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Yes, you can trust what you know. It doesn’t. I proposed boxing it with 1/8 if and only if too much deflection was observed under load (like with a go pro). Then I would add 1/8 to box, but never just slap thicker steel at the mount and sacrifice weight and elegance.
 
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