H3 custom cross member group design

[CaseyS]

OK, I've tried to repair the ends of my cross member to no avail. Its a frail design at best. I'm looking to get some input from the group on a redesign that will get to a fabrication step.

Given the weakness of the differential bushing, it would seem pertinent to evaluate a build from scratch and include whatever bushing design works best, not what fits in the hole. For the ends, I'm debating whether to cut the factory cross member up, lop the ends off and weld new ones on, or try and cut out the bolt guide tubes and weld in something more stout.

Modifying the end I feel still has some limitations in the torque direction front to rear. I'm leaning toward a machined solid end ear welded to a box section across the bottom. I think you could weld in a vertical section of DOM tube and use a shelf energy suspension bushing for vertical differential support, just set the top height correctly. Another option here would be to lower the member an inch or so to allow for a taller torsion lift while keeping the half shafts happy.

Open here to feedback here on a design for those of you that have seen how crappy the cross member is.

 

[4speedfunk]

Here's my cure...

Seriously...I think the whole design blows, (not just the crossmember). Why the H3 uses a horizontally-mounted biscuit type bushing is beyond me. Common sense should tell you that a biscuit like that can only take so many cycles of compression and tension before it fails. Frankly, I cannot believe a team of GM engineers couldn't see something so obvious. If you want to see what proper bushing orientation looks like...check out the GM 1500-IFS....

Notice the bushings are rotated, so on-off throttle shock loads are exerted onto the sides of the bushings. The fasteners (oriented to be cross-bolts) only see side-load in double shear...very strong. Also, having two bushings instead of just one helps a lot. Also, extending the bushing out on levers like this helps ease the stress on the bushings. This is how you mount an IFS. Its not rocket science...its just common sense. The bushings need to control the tremendous twisting forces that on-off throttle maneuvers can generate, and on the H3...the single snout bushing is nothing more than a body-mount. Not only that but, the single fastener (the bolt at the pinion snout) is not oriented to deal with on-off throttle loads. Its constantly being cycled between compression and tension forces...instead of the more desirable side-load that it would see if it were turned sideways. The whole thing truly looks like an fifth-grade shop class designed it. Sad.

Even if you do manage to get the diff securely anchored to the crossmember...then you quickly discover the problem CaseyS is describing. That is...the crossmember itself is often fatigued from on-off throttle forces. Not at the bushing location...but where it mounts to the frame! I'm sure it can be beefed up but, it doesn't fix the inherent shortcomings of the factory design. It needs a total re-think if you're going to put some real torque (diesel) through it.

 

[alrock]

Note that the OEM crossmember had two different designs. One version is a bit beefier than the other, but I cannot recall which is which. When Dwaine gets his cores in, he repairs and strengthens the ends.

 

[Synthetickiller]

Scorpworks has a thread on this & offers upgraded bushings: http://www.hummer4x4offroad.com/for...H3T-Scorpworks-Bushing-Front-Diff-Crossmember

That might be a simple fix.

 

[CaseyS]

The bushing is not the issue here. I have an upgraded bushing. The end mounting points of the cross member itself are pure junk.

If I try to build a full custom cross member, I'd like to hear all new fresh ideas on the table.

 

[4speedfunk]

I actually have a torched-off crossmember (see photo above) that is in my scrap steel box. If you want...I can save it for you. It has the mounting holes intact and would make a good jig to build a custom one, without having your truck torn apart.