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After spending too much time trying to figure out a good idea to add structure to replace my crossmember, I came up with an idea. Add a crossmmeber over the transmission. This should provide a way to prevent frame twist at the cab mount area. The original crossmember just wasn't going to fit under the C6 transmission. Any gussets or whatever I could add would have blocked the path for an exhaust system. When I took the cab back off the frame the solution looked pretty simple....tie the tops of the frame together, but keep it clean so there is clearance for the cab. Here's the idea:
That's not a bad plan at all. I might copy you when the time comes because I'm gonna throw my C6 back under mine, and I can already tell that I'm gonna have to use a mount that will only be attached to the bottom lip of my frame. But I wouldn't worry too much about it, because I can show you the opposite extreme. The PO had this metal strap under the C6 in my truck with nothing else. The thing bounced up and down so much with that heavy transmission that the 2 bolts they used on each end literally almost cut their way free from the frame. My truck was proof that pinion angle can change from second to second and the truck will still run down the road. But I certainly wouldn't reccommend it. Behold the most redneck transmission mount you'll probably ever see.
I made it out of 1/4 thick flat bar stock. I used countersunk bolts to keep it low. Between that and the trans mount at the bottom of the frame, and the boxed frame, I think there'll be enough support for the cab mounts.
Dan, I see you have have a Lokar Shifter your installing... Are you adding the neutral safety switch? I need to add one to mine, as it starts if it was left in gear...
Man, you have no idea. I actually took my kids for rides in that death trap before I tore it apart and discovered all of its issues. That bothers me to think about it. But I can honestly say that no irreversible damage was done by the PO. I'm just fixing a lot of stuff.
Old Dan, I really like that strap. You saw what mine had (or didn't have actually). When I tore my truck apart and started repairing the frame, I honestly could tell that the top of the frame rail was laid over a tad more than the bottom (probably like a quarter to half inch, but I could tell). I had to use a little bit of body english to get my bolt-in MII crossmember to agree with those rails. So I definitely think that top strap will help you a lot.
For my C-6 trans x member I used the original. I removed it from the stock location and moved it back approx 8 inches. I made up a bracket and welded that to the cross member, drilled it for the trans pad and bolted it in. The only thing different is that the frame is about a half inch wider here so I made up two spacers for each end of the cross member. Everything went back together like it was made for it. It was pretty easy to do.