If at first you don’t succeed…

I spent most of a day this past weekend making a cool, nice-looking transmission crossmember for our Unfair Camaro project. Unfortunately, it sucked. To be more specific, it flexed downward 3/16″ when the weight of the transmission was placed on it. I made it out of high-grade 4130 rectangular tube, with proper welding and great fitment. It looks really good. But, as I said, it sucked.

I was lamenting this state of affairs to my friend John (a materials/mechanical engineer with a military firm) when he asked me why I was stuck on using an OEM based design with the insulating material (rubber or polyurethane) in the original place. Why not, he asked, move that material to the body side of the crossmember and get it away from the transmission itself? I thought about that for awhile and then John called back with a comment from another engineer friend of ours, Glenn, who said that the span of my original crossmember was a big problem too. I needed to make the crossmember shorter, which will minimize deflection a lot. Making the crossmember shorter meant I had to move the body interface from the subframe frame rail to the floor.

A bit of luck was with me: the location of the subframe reinforcement rib was welded to the floor at just the right location. I could weld tabs directly to the floor and they would be incorporated in the same structure used to bolt the subframe to the car. Perfect. So I made another crossmember, this time using a pair of poly rod ends (from AME) I had originally bought for II Much but hadn’t used. Putting the insulating material outboard of the transmission itself makes the whole setup more compact, with a big bonus of giving me more floor space for the humongous exhaust to come.

New crossmember.jpg

Here’s the new crossmember. It bolts directly to the transmission and save space and weight compared to the original design. I used spacers between the rod end and the body tabs to give us some fudge room when we put the real transmission in.

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