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TC rod pivot relocation / Bad Dog subframe connectors / Slotted Crossmember


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Well, it looks like 2x4 tubing is definitely going to be the route to take. I installed the strut and took it through the range of motion. No binding at all if the rod end was right in the middle of the slot. It actually worked really nicely right there. When I moved the rod end down as far as I could I found that I couldn't utilize the whole slot because the rod end hit the top of the bracket. This limits my total adjustment to about 3/4" which is less than I was hoping for. Also, I couldn't move the suspension all the way through it's range before the TC rod hit the bracket. 2x4 tubing will definitely solve both of these problems. I took some more pics:

 

This shows how far I can move the rod end before it hits the top of the bracket.

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LCA angles at FULL droop. Should be just slightly pointing down at race ride height.

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TC rod hitting bracket at less than full bump.

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So with that in mind, any opinions on the 1/8" tube for the 2x4? Stiff enough? I was still going to brace it to the rockers, so maybe with that in mind it would be enough?

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Attempt #2: This time using .120 wall 2x4 tubing. Changed up the design just a bit. I left more meat out back and I decided to contour the tube like John suggested. This will allow the the tubing to connect on the top and the side.

 

Haven't cut the slot yet as I haven't gotten a new 5/8" bit, but I did get one side kinda roughed in. Cut the shape with a cutoff wheel. I'm going to clean it up with a grinder and then the dremel. I have to say that it looks like it's gonna work out really smoothly.

 

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Bad news: Getting a little fed up with this project.

Good news: It's almost done.

 

I welded on my TC brackets today, along with a support that attaches to the rocker for each side. When I welded the brackets to the frame I grabbed one and wiggled and you could SEE the frame rail flex. That frame rail is sheet metal thin!!! Kinda scary... :weird:

 

I'm glad I did the braces to the rockers. Where I attached to the rocker is actually pretty thick and strong, so that part at least should give some support. Once I got the braces welded on I could no longer sense any flexion, but being that the frame rail was that weak I gotta assume its there. I'm still thinking of other ways to make it stronger, like turning the crossmember into a K member. I don't want to do it though, then find out that my oil pan or exhaust doesn't clear or something stupid like that.

 

My brackets ended up having only 1 1/8" of adjustability in them due to interference issues with the frame rail. The nice part is that it coincided perfectly with my previous crossmember slotting. The crossmember slot went from 3 3/4" to 2 5/8". The new TC bracket is slotted from 2 3/4" to 1 5/8". So they're just right, since the stock setting was to have the TC pivot one inch higher than the LCA pivot.

 

I still have to connect the subframe connectors to the bracket. That got a little tricky because of the curve of the frame rail down towards the bracket, but I think I've got a handle on it. I did have to leave a little gap to allow room for the bolt head fit in the slot when the TC rod is all the way up.

 

I think this will be done in a day or two, then I can move onto something else... finally. Maybe I'll get back into the roll bar... :D

 

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What about a gusset underneath the TC bracket, 90 degrees to the frame rail, attaching it to yet another side of the frame rail?

Funny you should mention that. I was going to do that tomorrow with a piece of angle iron, just welding it in from the top of the frame rail down to the bracket.

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Didn't quite get it all done today, but it's 95% there. Got both subframe connectors done. Need to finish patching the rail in front of the TC box, and I didn't get to the angle iron that I mentioned yesterday.

 

I think I figured out why my car was so twitchy under braking today. The passenger side frame rail above the TC rod had a 1" long crack! The crack was hidden under some of the factory undercoat. And that's thin sheetmetal that was cracked!!! I think this came about from the damage that the car had on the passenger frame rail. It looked like the PO had ran over a curb or something. I never paid too much attention because it aligned out OK even before I had all the adjustable suspension. I guess that is a word of warning for anyone else who has banged up frame rails. So I welded up the crack and got the frame rails done. Had to bend the frame rails to follow the curve of the Datsun rails, and I also had to patch a long triangular section because the frame rail curves in near the TC box, and my Bad Dog special order parts did not. Thanks John, they worked GREAT. Again, if I weren't doing this freaky TC rod modification I think it would have been a couple hours labor to put these things on, and I really feel that they will add a lot of rigidity to the structure of the car. :2thumbs:

 

Check out the crack!

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See it NOW?

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This before shot is just UGLY! Lot of filling with the welder, but I didn't really see another option...

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After:

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Yeah, my gut tells me that crack was actually pretty significant. So what do you think about the overall fix? It's kind of hard to get a plate in there to cover that crack because it's a weird curved surface there, so I didn't, but I figure with the reinforced frame rail/subframe connector, the planned angle iron gusset on top and the thicker TC bracket and the brace to the rockers it should be OK. Do you think I did OK?

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If the damage is from an accident, the repair you've done will be fine. One trick on crack repair is to drill the very end of the crack (the root) with a 1/8" bit to spread out the concentration of force where the crack is continuing to grow. Then weld from that point back to the start of the crack.

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Well, I do believe the TC rod pivot relocation project is officially done! :D

 

I was thinking this morning about patching the frame rail in front of the TC bracket, then it suddenly occured to me that I still had the end of the Bad Dog rails. Remember these?

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So I figured if I was going to cut the shape in the bottom of the frame rail into a piece of steel, it might as well be those! Line the angled section up to the TC bracket, and now I'd have gusset in another direction. So that's what I did. The angled section was about 3/4 of an inch too tall, and about 5 inches too long, so I trimmed it down for length on the chop saw and cut the angle on the band saw. I did also do the angle iron gusset that was previously discussed. Pics:

 

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All in all I think this whole thing turned out pretty damn good. Figure a 10 - 12 lb weight gain, but I got subframe connectors, I can adjust dive and anti-dive a bit, got what looks to be a MUCH stronger than stock TC mount, strengthened my seat bracket, and found and fixed a crack in the frame. Not too bad!

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Dam cool indeed!

 

fwiw you ideas and exploration of a seldolm tackeled subject have givin me a ton of insight on the tc rod in the grand scheme of datsun FR suspensions, I hope to put your(and others who have chimed in, johnC, tube280z to name a couple) theories and experimentation all to good use very soon.

 

Cheers!

Sam

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  • 4 weeks later...

It's a support that was mentioned by preith and is used on his GT2 car. I'm still thinking there might be a K-member type mod to the crossmember, in which case the K member to the TC rod bucket goes straight through this same plane.

 

Whether or not that brace alone will do any good I can't really say. It does look counterintuitive, but it was easy to do and the thin wall tubing weighs next to nothing, so I did it anyway.

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  • 1 month later...

I welded on my TC brackets today' date=' along with a support that attaches to the rocker for each side. When I welded the brackets to the frame I grabbed one and wiggled and you could SEE the frame rail flex. That frame rail is [b']sheet metal thin!!![/b] Kinda scary... :weird:

Yikes, flexing frame rails... Now I'm really glad I had my rusted rails cut and replaced : )

 

Now sporting new 9 gauge (3 mm) custom rails 2.36 x 2.36 inch (60x60 mm)

I'm hoping my rails will be left out of the flexy-rail club.

 

Great thread, picked up some ideas along the way thumb-up.gif

 

Hope you'll post pics of the finished/painted install!

 

Cheers : )

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