T/C rod bracket to subframe connector connector

[Guest bluex_v1]

I need welding help, other advice--

Right now I have a really crappy buggered weld transition from my 1x2x1/8th tubing subframe connector to the boxed sheetmetal frame rail that I'm sure will probably fatigue too soon. I'm also concerned about rust flourishing in that large boxed area that I might not know about. I'm a little more confident in my welding skills now and I want to redo this area for a few reasons:

I want to get greater strength, especially braking force transfer to rest of car, while allowing a much stronger joint between the 1x2x1/8th subframe connector and the front half of the car to combat flex at the firewall. I think I should also get some added strength to the T/C bracket itself since that is carrying most of the engine weight on my install.

I also need better access to the inside of the framerails anyway for rust repair/prevention. I can do this, I think, one side at a time without affecting the suspension or body geometry. I'm willing to trade some weight for the strength and peace of mind here. I do not want to replace the entire frame rail assembly with tubing all the way up to the bumper, because I don't trust myself to get the measurements exact and I don't want the extra weight up that high, and I won't get much engine load carrying benefit out of the full tube framerails since I'm not going to be putting as much weight on the front crossmember compared to a SBC install.

I'm planning to:

-Place a jackstand under subframe connector within a few inches of where the floor angles up to the firewall.

-Place a jackstand under engine bay framerail just in front of the T/C rod bracket, and another jackstand just behind the bumper bracket.

-Cut out bottom of framerail box so I can attach a diagonal 1x2x1/8th peice of rectangular tubing from the bottom rear of the T/C rod bracket to the front of the subframe connector where it terminates at the end of the flat portion of the floor.

As far as I can see, my main problem is in joining this 1/8th inch wall tubing to the remaining sheetmetal box of the framerail. I am going to need to allow some flex between the tubing and the sheetmetal right? I'm guessing, 1/2 inch on 1 inch off intermittent beads attaching the bottom edge of the framerail sheet metal to the top edges of the tubing, and then maybe a strip of 4 inch tall 20 gauge sheetmetal on each side covering up the tubing-to-framerail box transition, welded 1 inch on 1 inch off to the bottom edge of the tubing and then just tacked up top to the sides of the remaining boxed framerail.

Now I know the boxed frame rail is something like 2.5 inches wide right? would I maybe be better off with a 3 inch wide peice of tubing and just reducing it down to 2 inches right as it transitions to the subframe connector? either way, I'm not sure how to go about that transition from tube to sheetmetal.

I was also thinking about adding a few gussets, one or two triangular ones on the back side of the T/C bracket and then a couple peices of flat stock on the three exposed sides of tubing where the diagonal attaches to the subframe connector.

Are there any things I should know that make this a bad idea, or something additional to make it better? Thanks, especially if you managed to read all this

[Jeff]

That sounds very similar to Pete Paraska's setup and you can check out his website here

 

I would recommend removing that sheet metal box entirely so that you can tie into the TC bracket and frame rail properly. That box is welded to the TC bracket really well and it took a lot of grinding to get mine off. I'm planning on doing this and I thought I would cover it with a sheet metal piece when I was done. The sheet metal would just be to make it look more finished. Here is what you have left once you remove that cover.

 

 

I know it's not a great shot of the area but I hope you get the idea.

[Guest bluex_v1]

Yes, shame on me for not consulting the bible, er..Pete's site...I guess I never really noticed his subframe connectors come all the way forward.

I'm with you on cutting the whole box out of there, mine is probably junk anyway.

I suppose the thing I'm still not clear on though, is since I'm not going to be putting in a new frame rail up on the top like Pete, is it structurally important that I have the box 'cover' portion there? Can I just have the stock square frame rail up top and the tubing on the bottom with air in between? (as a side note, I wonder if having an escape for air that would otherwise be forced into the transmission tunnel would help reduce front end lift ever so slightly) I think this is the space you were referring to about covering it up to make it look more finished right? but are those walls of sheet metal offerring any fore-to-aft sheer(?) resistance? and if those are structually important, what would be the best type of welds to use?

[Jeff]

Those sheet metal boxes are welded in very well and I suspect that means that Datsun considered them a structural element. I would tie the factory frame rail to your sub frame connector with gussets or some short pieces of tubing run vertically off of you sub frame. Or run a piece of tubing against the angled section where the floor pan transitions to the firewall and tie into the factory frame rail where it meets the firewall. You could then leave it open.