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JMortensen

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

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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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What does the 1x1 support tube do? It doesn't seem to be strong in any useful direction. Any force transmitted through the TC rod will be axial (no moment). This would put a direct moment on that tube which is its weakest direction. Is this for support for a force other than the forces through the TC rod?

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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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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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I guess this crossmember stuff fits in this thread pretty good. Didn't feel like it warranted a whole new thread. Anyway, I finished up my front crossmember mods. This ties into the TC rod mod a bit. The crossmember is slotted for pivot height adjustment, the rack is moved back about 7/8" for Ackerman, the stock rack mounts are gone, no more bushings. Had to clearance the crossmember for room for the pinion housing, filled in that area with a piece of pipe.

 

Installed the crossmember, double checked everything, then took the plunge. I stitch welded the crossmember to the frame rails and welded some supports from the crossmember to the TC brackets, making the crossmember into a K member. I also stitched the crossmember seams while I was at it. I'm hoping this front end should be pretty stiff... :D

 

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i installed my mad dog frame rails. i had them make me an uncut front section so i could fab a better fit. jmortensen, looks like you stitch welded your rails on. i stitch welded mine on too, then went back and filled in the gaps so it formed a weld bead down the whole length of the rail. i know that might not have been the optimal route to go, but it looked like crud could have easily gotten into those gaps and caused more rust troubles down the road.....

 

should i have just left them stitch welded?

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I figure that the stockers were just spot welded, so I didn't get too obsessed with sealing the seam. Speaking of which, if I were to seal the seam, I would use seam sealer instead of welding the whole thing. Besides, mine aren't sealed up against the floor in back either...

 

I don't think you really hurt anything, but I think stitching is theoretically stiffer than seam welding.

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The bracketry looks nice but it appears you've drastically shortened the TC rod. This is not a good thing because it makes the caster sweep really bad. Ideally you'd like the TC rod and the control arm to be as long as possible. That would minimize the geometry change.

 

Two ideas to fix the caster issue would be to either relocate the bracket and use a longer turnbuckle or make the control arm into an A arm instead of a control arm and a TC rod.

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ya i agree. after seeing it all together i think i prolly end up rebuild the arms. it never clued in to me up to the point when i was welding the arms up that with the 240sx rear it is a couple inches wider in the back. so im going to end up makeing new longer arms to match the width in the rear. and i agree the tc arm looks to short but i think it looks shortter than it is. because it mounts to the control arm ferther in board. and the amount of frame behind the "tc box". im no expert but whats a bad castor sweep. my understanding is that once set with this desighn castor would be the same no matter what the static legnth of the arm.

jon...

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i had a shower and thought about for a bit i get what you were saying about castor change. prety much what im going to have to do is rebuild every thing. but one of the next things i want to do i get the car to my work and put it on the rack and do a alignment just so i can see if the dang thing will go straight. this set up will do enough for test porposes. ive sloted the kmember that very nicely gets rid of bump steer but it also raises the front rool center quite a bit. i think once i get my engine test fit im goign to make a k member that adjusts the control arm height but also can move the rack up down forward and backward. for a truely adjustable front end.

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Jon, would you be able to update all the images, or just repost the finalized stuff, etc. for this sticky?

 

Also, another (probably stupid) question; If you go through the trouble to make a new T/C rod mounting point and fab your own T/C rods, why not simply fab another point like the subframe mount for the lower control arm and make it a standard control arm with two mounting points like the rear lower control arm? This avoids the whole caster issue cause by the arc the T/C rod sweeps since both chassis side pivoting points would have precisely the same pivot axis.

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I don't see a control arm as an advantage vs an LCA and TC setup. You can't lengthen the control arm in that type of setup, and when the caster angles get extreme the arm starts to point forward, which makes it act differently than an arm that is perpendicular to the center line of the car (the reaction to this is discussed at the very beginning of this thread). It would also eliminate or at least make much more difficult the ability to add in adjustable anti-dive and front roll center. The potential benefits would be tire clearance and possibly weight and strength, but above and beyond that if there are any I'm not aware of them, and I'm not really worried about the weight or strength of the pieces as I've modified them.

 

Floor with stock rails cut off:

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Pulling floor to SFC with sheet metal screws. Also shows custom piece Bad Dog and roostmonkey made for me:

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Stitching the SFC's to the floor:

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Cut the entire TC bucket and the supporting frame structure off:

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The seat bracket lined up with the SFC perfectly:

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Weird shaped hole cut into top of new TC box to line it up with bottom of frame rail:

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TC box setting on frame rail:

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Shot shows the now slotted TC rod box, forward gusset, the modified Bad Dog SFC connecting to the TC box, and the support from the box to the rocker tip.

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Angle iron gusset on top of TC box

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Mocking up the TC rod angle to make sure the rod didn't hit the box through the suspension travel.

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Believe it or not there is a new development on this project. I never did make my new TC rods previously. I ordered up some turnbuckles and they were too long, then I just used the old rods on the car to move it to the new house. So now that I'm about to paint the undercarriage I finally decided to make new TC rods. Got a new turnbuckle, a 3/8" clevis and a piece of 3/8 x 1 bar stock and went to work.

 

Based on info from another thread I tried to make the TC rod point directly at the ball joint. This is supposed to load the rod itself better (straighter). I think I did a pretty good job at aiming the rod, but now the piece of bar stock is pretty long and I'm thinking that in itself might be a weakness. I guess I'm considering drilling a new hole closer to the control arm, even if it loads the bar a little bit off dead center. I remember Cary talking about cars on slicks bending the stock TC rod at the bend. I would imagine mine is a little stronger at this joint than a stocker, but I'm not sure I want to take chances here.

 

Thoughts?

 

 

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Jon,

 

The design will work if you redo the plate on the control arm such that it also captures the outboard bolt on the ball joint. The current design places that bar in bending when you apply the brakes. The other issue that you may encounter is the tire rubbing the T/C rod when turned fully to the left or right.

 

As you know, I had an issue with my T/C rod a couple of years ago. As part of putting my car back together, I reengineered my T/C rods similar to what you have. The plate that I use on top of the control arms uses the same two bolts as the stock T/C rod. A third hole in the plate lies on the line drawn between the rear-most bolt on the plate and the T/C pivot on the frame. I'll have to borrow a camera, so that I can post a picture.

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How about welding on a tab like this? Seems like it makes the TC rod connection double shear which was something Cary had mentioned, and it also gives another load path for the rod to the control arm. The tab has a slight bend to it in order to hit right on the edge of the control arm, but I don't think that would be too much of a problem...

 

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Well I went ahead and welded tabs on both arms. There is also a reinforcing plate on the arm underneath which stops about 1/8" from the edge of the arm, I welded the gap up so that there is a solid 1/8" thick or thicker piece of metal from the TC rod all the way across the top of the control arm. This just looked like such a naturally good solution that I figured what the hell...

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