Are the trans cross members of 3rd and 4th gens interchangeable? Can I put a 3rd gen crossmember into my 4th gen? If not, why not?

 

no they will not, the third gen xmem and 4th are 2 totally diff designs. i dont mean a few inches off and make a few minor mods and it fits kinda diff, i mean totally diff design.

 

Yeah, 4th gens are almost "L" shaped and 3rds are flat. I was thinking of running the 3rd gen secondary trans mount for reduced vibes from the poly trans mount.

 

3rd gens don't have a secondary trans mount.

They have the crossmember to which the transmission tail shaft bolts, and then TQ arm bolts to the tail shaft itself.

 

Yes they do. Particularly the late v8 camaro rs. it was to reduce vibes. But most third gens didn't. It was a two piece crossmember with two bushings and a main mount that attached to the tails shaft. It's definitely odd looking, but looks like a smooth ride

 

that sounds like a TQ arm mount and that was standard on all third gens.

 

This.

There rubber mount with a stud that points down and threads through the x-member, that gets a nut on it. I think 15mm.

Then there is a clamshell type mount which holds the TQ Arm.

4th gens are the EXACT same way. The TQ arm mounts to the trans, and the trans mounts to the X-member. The only deviation is that 4th gens also sometimes have a secondary front sub-frame brace after of the cross member. This brace is to stiffen the front sub frames, but in no way does the transmission mount to it.

 

Obviously you guys dont know about this:

Secondary Cross Member? Junk it. - Third Generation F-Body Message Boards

 

dosent sound like a secondary, sounds more like an alternate style. i'v been under multiple third gens and thats the first one of those i'v seen.

 

Whatever you feel it needs to be called in order to validate its existence.