'29 coupe sub frame

[Vin-tin]

My coupe body is all apart down to the sub frame. The only thing that remains is the cowl and latch pillars and the seat riser sheet metal.
The rear half of the sub rails are more rusted than I had thought, so now I have to decide on replacing them. I have riveting tools and some experience. I'd like to here pro's and con's from you guys on replacing full sub rails vs just the rear sections.

Also, the rear cross member has no D-nuts. I need access to the inside to install them. Are the inner and outer channels welded together?

[wrndln]

You don't need to get inside the rear body cross member to install the D nuts. On my phaeton, which is very close to your coupe's rear body crossmember, had all the D nuts missing. I fished the correct D nuts (12-24 I believe) in from the end (there are holes there) using a wire with the wire around a machine screw threaded into the new D nut. It is a tedious operation, but with a little patience, I got all the D nuts inserted into the crossmember holes. I used my MIG and tacked the D nuts to the crossmember (see pictures).

As far as either replacing the subrails or not replacing them. The subrails on my 28 special coupe were badly rusted out on the outside leg where the read fender wells are (see pictures). I cut the outside leg off and welded 14 gauge metal to the top part. it worked out very well. If you replace the subrails, it is quite hard to make sure all the holes for the rivets are in the exact spot they should be. It is a lot of riveting to rivet the cross sills and other panels to the subrails. I wouldn't replace the subrails unless they were very badly rusted out. I also had to repair the spot where the rear body block hole was as it was really cracked and damaged.
Rusty Nelson

[Vin-tin]

Rusty, my rear body mount area on both sides are bad also and my rust over-all isn't quite as bad as yours. However, I feel as though I went this far tearing it down, I might as well replace the rails. I was just wondering what most guys do...replace the whole rail, or just the rear half?
Either way there's riveting involved and getting every hole near perfect.

Also, I re-posted your picture. If the rear cross member isn't welded together, removing 4 more rivets on each side (red arrows) will allow me to install the d-nuts easier, and also to sand blast and prime everything inside the channel.

[Manager]

Good job Rusty.

[Vin-tin]

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For anyone who's interested, the rear cross member is spot welded together. I cut about 9 or 10 welds and it popped apart. That allowed me access to do the necessary welding to close up the extra holes someone added, and to blast all the rust away inside. Installing the eight D-nuts was also quick and easy.