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

[JMortensen]

As I am finishing stitch welding the inside of the car, I am realizing that the next part will be the front frame rail seams.

 

I've been thinking of relocating the TC pivot up to match the already raised LCA pivot, and I've been trying to figure out how to do it. Cary got my brain working about a couple months ago by saying that I should use a bolt placed vertically, then space the rod end up or down with bump steer spacers. Then BRAAP pointed out that the TC pivot really should be in line with the LCA pivot, otherwise braking loads can compress the suspension.

 

So here's what I'm thinking. I'm thinking of cutting the TC box off of the frame entirely. I'm also thinking that the reinforced part of the frame rail behind the box which ends up attaching to the floor can also go.

 

I like Cary's idea and I want to use it, especially after seeing how the BMW LCA mounts in one of John Coffey's threads. The question is how to do this? I haven't done any measurements yet, but it looks like the pivot needs to be about an inch or so inside the inner wall of the frame rail. So here's my idea: Get a long 5/8" bolt (lets say 6" for this example). Weld a couple clevises, one on top of the other, to the inside of the frame rail. The bolt slides down vertically through the clevises, so that it is now going through 4 layers of 1/8" plate. The idea is that the bolt should have 4" that are totally within the clevises, and maybe 2" sticking out the bottom. In my non-engineer mind this seems like it would make the end of the mount stiffer and possibly allow it to deflect less. Then close up the clevises with a piece of .105 inch plate (cause I already have it) to make basically a triangular prism shaped box that locates vertically on the inner frame rail that holds the bolt.

 

Next problem is beefing up the frame rail to support the load. My thought here was a couple of plates with some 1" square stock in between that attach the inside of the frame rail to the outside of the frame rail. This will make sure that one side of the rail doesn't take all the load. Then brace from this plate on the outside of the frame rail diagonally to the rocker as Preith had mentioned in a previous post.

 

Might even be able to do a K member type mod to the front crossmember so that these loads are spread as much as possible.

 

For what it's worth I'm also going to do a subframe connector, so the front frame rail won't JUST be attached to the firewall and the rocker.

 

The questions are:

 

1. Will the frame be significantly weakened by the lack of the TC box structure? It looks like that structure is there just for the sake of the TC rods as originally placed by Nissan.

2. Will my vertical box be strong enough to take the braking loads if I reinforce it as described above?

3. Anyone done anything similar?

4. Does anyone have a better idea?

 

Looking forward to your responses.

[JMortensen]

Just did a quick measure with a square. The center of the front control arm pivots are 5/8" inside the frame rail. So that means these clevis type pieces would have to be very small. The bolt would basically have to sit 1/4" off the inside frame rail. This probably means off the shelf clevises wouldn't work. Might have to make a bracket instead. Still thinking...

[JMortensen]

Nobody has anything for me??? Kinda surprising.

[74_5.0L_Z]

When I built my replacement frame rails, I moved my T/C pivot up 3/4" and out 1/4" to mimic the relocation of the LCA pivot point. I replaced the entire front frame with 2.5" square tubing per the original frame dimensions (except the T/C pivot point.

 

I made my clevises from 2" x 3" x 3/16" rectangular tubing. I scribed the outline on one side and located the holes, and had my buddy at the machine shop cut them out. The part that overhangs the inboard side of the frame rails is gusseted from above. I made a fixture to locate the clevises for welding.

 

My reasoning was the same as yours: I didn't want to design an anti-anti-dive front suspension:)

 

[Jolane]

Ah Ha, that is exactly what I was talking about in another thread a few weeks ago 74_5.0L_Z. That looks great. The thing I like most is the ability to now use a rubber/poly bushing instead of the rod end, just for vibration.

That looks really nice. I think it is definitely better than the typical solution of boltsing on a "clevis" to the stock TC rod mount. I am not sure I will go that route, but thanks for the picture. I will decide in a few weeks.

 

Joshua

[260DET]

74's setup looks good.

 

Jon, my car is lowered a fair bit and what with all the other things I've done with the front end the question of tension rod operation has been considered at length. But seeing that the car behaves perfectly well under heavy braking, regularly down from 200kph, the 'if it aint broke don't fix it' maxim has been applied. This is with front toe out too.

 

But what has been done is to run a light straight removeable Xmember* under the sump from tension rod chassis pickup point to point. The idea was to prevent side movement of the pickup points under braking. Make of that what you will but there it is.

 

*made of ~30mm square section tubing.

[JMortensen]

I guess the idea for me is that I want to change around the pivot heights some more. I suppose I could make a new TC box like 74 has and slot that. I do have my front crossmember slotted after all. I would prefer to have the most rigid mount I could get though and it sure seems like the bolt held by the frame might be stiffer than a large box that's welded on one side. I realize that this is why the box is 3/16" thick, and I have a friend who basically did the exact same thing on his 510 and it works well enough for him. My friend just drilled a hole at the stock pivot height, then drilled another one to match his raised control arm pivot, and that seemed to work well enough. I guess I just like Cary's idea better.

 

Maybe I'm wasting effort...

[tube80z]

Nobody has anything for me??? Kinda surprising.

 

Some of us are also out in the shop putting mandatory vaction time to good use too

 

I need to take some pics of the car and get back to you on this one. May be a day or two as I'm in the middle of a project too.

 

Cary

[JMortensen]

Can't wait to see what you've got for me Cary. Thanks.

[JMortensen]

ttt

 

Cary, you out there?

[tube80z]

ttt

 

Cary' date=' you out there?[/quote']

 

Yes, I have a few things I'm trying to finish for you. Power point isn't working so well for a CAD system. Check back later tonight and I should be done.

 

Cary

[tube80z]

The questions are:

 

1. Will the frame be significantly weakened by the lack of the TC box structure? It looks like that structure is there just for the sake of the TC rods as originally placed by Nissan.

2. Will my vertical box be strong enough to take the braking loads if I reinforce it as described above?

3. Anyone done anything similar?

4. Does anyone have a better idea?

 

So here's what I'm thinking. I spent a little time looking at this over the weekend and I didn't see an easy way given the frame rail is curved. If you look at 74_5.0L_Z's car he has flat frame rails and the TC box could be simpler.

 

Don't laugh at my great power point CAD skills

 

 

The idea would be to cut out around the round area to open it up for the TC rod to pass through (the red lines). The green lines would be a doubler plate on the frame rail that gussets from the original TC box would go to. Not shown would be the back side of this covered so that it forms a box. Hopefully that makes sense.

 

For the adjustment I'd use two safety washers and aluminum rod as bushing material. This would give you good range of movement and an easy way to have bushings cut that would raise or lower this pivot.

 

Now for the underbody brace I was looking at doing a triangle like this under the engine bay.

 

 

The tubes from the rockers would be welded into the TC box. From the TC box to the crossmember I'd make these bolt-in using countersunk machine screws. I don't have a pic of this but you essentially slot the tube and weld it to a flat plate. The idea being that it is strong in tension and weak in compression. So if you ever had a major collision the engine could still eject out the bottom.

 

Hopefully that helps. I couldn't figure out how the clevises would work that you described above. Wanna take a shot at a visual of your idea?

 

Cary

[JMortensen]

OK, I see where you're going. I'll try to get some sort of a visual representation of what I'm thinking once I get home, so probably tomorrow. I've got some frame rail damage behind the TC boxes, so eliminating those completely means that I get the side benefit of not having to repair that area...

 

Thanks!

[johnc]

One way to think about the LCA/TC combination is as a lower A arm. Looking up at the bottom of the car (as in the pictures above), there is a triangle formed by the LCA (side "A"), TC (side "C"), and an imaginary line (side "B") drawn from the LCA mounting point to the TC mounting point. That's the A arm.

 

Ideally, there should be a 90 degree angle at the A/B junction. This requires an articulated joint at the B/C junction unless the orientation of the B/C junction can be made to allow parallel movement between the A/B and B/C junctions. If I was going to mess with the TC rod mount, I would do what I could to make this whole setup operate exactly like a true A arm.

 

A long rod run through the LCA inner mount and clamped/tack welded to be at 90 degrees to the LCA and parallel to its pivot axis would give me a great indication where the TC mount needs to be and in what orientation.

[JMortensen]

OK, maybe these pics will help. The clevis was cut off of the rear strut towers. My old strut tower bar setup used these clevises, but John and Drax convinced me to weld a solid bar in there. Thanks for that guys.

 

So here's the idea. Build basically a triangular extension off of the frame, then put the bolt down vertically through it so that it sticks out the bottom. Use spacers to set the height of the rod end, and a nut on the end to hold it all together. That is a 1/2" bolt and the actual bolt would be 5/8", but that was the only one I had to use for the model.

 

This is kind of similar to the BMW front LCA mount that John showed in another thread which had a stud sticking directly down out of a frame rail, or for a Z comparison it might be sort of like the Mustache bar bolts which stick straight down through the frame. Only on the end of this bolt would be a series of spacers (bumpsteer spacers is what I was going to use) which I could reposition as needed to move the pivot up or down. I was going to do it in single shear, with the bolt supported along several braces within the frame rail, and the end of the bolt sticking down to accept the rod end.

 

My frame rail on the passenger side is really beat up behind the TC bucket. I think the PO must have done some off roading or run over a curb or something. I know that the car is still straight because I never had any thrust angle alignment issues on the car, but I'd like to cut that crappy section in red in the last pic completely off the frame rail if I can.

 

The original idea was to use 2 clevises and weld them one on top of the other to the side of the frame rail, but they are obviously too tall. You can see that if I were to use the clevis the TC pivot would be further inboard of the stock pivot location. I was going to make a triangular frame extension there and then drill the hole in the correct location, which locates the center of the pivot bolt .625" inside the frame rail.

 

The more I think about it the more I'm questioning John's idea that the A to B junction NEEDS to be at 90º. Seems like the rod end I'm using on the LCA pivot can still move straight regardless of the angle that exists there. In fact that was why I went to the rod end in the first place. When I added a bunch of caster the LCA bushing was REALLY tweaked, and the rod end got rid of the stiction there. If I'm missing something and it was preferable to have the LCA at 90º from the frame rail I could always change the spacers on either side of the rod end to square it up, but I really don't think that this is an issue at all (although it would be a BIG issue if you're using bushings which can't handle the misalignment).

 

Also had another thought relating to 74's idea. I could weld a piece of square tubing to the bottom of the frame rail as he did, then drill a hole through it and have my bolt in double shear, and space it up and down as in Cary's picture. Kind of a combo of 74's idea and Cary's. I just don't like that it would be supported at the top on the one side of the box only. My idea gives more structure to the area that supports the bolt I think.

 

Cary, I don't think I'll use your idea as pictured on my car for a couple reasons. One, getting the original TC rod box off the frame rail is a goal, if it can be done. Two, your design would move the pivot further inboard of the frame rail, which would mean that I'd need to move the LCA pivot inboard to match. That's not a bad idea at all, but it would mean that I'd have to redo my LCA's again because their length is close to maxed out as it is. I know it would be technically a better solution to lengthen the TC and the LCA, but I've got enough crap on my plate for now...

[74_5.0L_Z]

Just be careful that you have sufficient clearance between the frame and T/C rod after you relocate it. I redid my T/C rods before sectioning my struts, and had no problems for over a year of driving/ autocrossing. I then lowered my car and sectioned the struts. Unfortunately, I did not recheck all my clearances and my tubular T/C rod hit the corner of a plate that I had welded to the bottom of my frame rails(remnants of my old motor mounts). The result was that the dented T/C rod buckled and broke under hard braking on a very tight course.

 

The following picture shows the results of a trip through the mangroves at the Bay Bottom Crawl. The left front fender, hood, and air dam were destroyed. The left side mirror, Quarter emblem, radio antenna, and rear side marker were ripped off the car (and are still somewhere in the mangroves), and left the driver's door with pressure dings. If you look on the ground in front of the car, you can see the failed T/C tube.

 

 

I have nearly finished repairs (SubtleZ body kit), and have reworked my T/C rods for added clearance. I'll post pictures when I get some.

[johnc]

The more I think about it the more I'm questioning John's idea that the A to B junction NEEDS to be at 90º

 

I phrased it wrong to try and make it easier for folks to understand. The critical part is to make sure the pivot points at B/C (near the existing TC rod mount) and A/B (LCA mount) are in the same plane in relationship to the LCA (side A).

[JMortensen]

Sorry if I'm being dense. Are you saying that the LCA mount and the TC mount should be in the same line relative to the center line of the car? Because that's really the whole reason I'm doing this. This is supposed to be an easy way to get the LCA mount and the TC mount in line front to rear.

[tube80z]

So here's the idea. Build basically a triangular extension off of the frame, then put the bolt down vertically through it so that it sticks out the bottom. Use spacers to set the height of the rod end, and a nut on the end to hold it all together. That is a 1/2" bolt and the actual bolt would be 5/8", but that was the only one I had to use for the model.

 

Thanks for the pics, those helped a ton. My only reservation on all this would be mounting this bolt in single shear and adding spacers to it. I think you could get away with it in single shear (similar to a balljoint on the bimmers) only if the spacer was really short. It would be much better all around to make the mount double shear. I'd also make sure to have as close to the amount of surface area for the bracket as the original.

 

This is kind of similar to the BMW front LCA mount that John showed in another thread which had a stud sticking directly down out of a frame rail, or for a Z comparison it might be sort of like the Mustache bar bolts which stick straight down through the frame. Only on the end of this bolt would be a series of spacers (bumpsteer spacers is what I was going to use) which I could reposition as needed to move the pivot up or down. I was going to do it in single shear, with the bolt supported along several braces within the frame rail, and the end of the bolt sticking down to accept the rod end.

 

If you decide to go this way I'd use a tube to support the bolt rather than the clevis idea. The top could wrap over the top of the frame rail and the bottom the same. The tube would be welded to a plate that would cover the inside of the rail. Very similar to the clevis but with more surface area. I would stack spacers in this application. I'd make them one piece. I'd also suggest looking for a nord-lock washer system in this application to keep things tight (http://www.nord-lock.com/)

 

My frame rail on the passenger side is really beat up behind the TC bucket. I think the PO must have done some off roading or run over a curb or something. I know that the car is still straight because I never had any thrust angle alignment issues on the car, but I'd like to cut that crappy section in red in the last pic completely off the frame rail if I can.

 

In looking at this on my car it appears it could come off. I do think it adds to the strength of the rails but how much off it is used for taking the load the TC box would be a question. If you look at what 74_5.0Z's car you'll see that's pretty much what he did and I really like it. Bummer on the off, BTW. It was such a pretty car.

 

Also had another thought relating to 74's idea. I could weld a piece of square tubing to the bottom of the frame rail as he did, then drill a hole through it and have my bolt in double shear, and space it up and down as in Cary's picture. Kind of a combo of 74's idea and Cary's. I just don't like that it would be supported at the top on the one side of the box only. My idea gives more structure to the area that supports the bolt I think.

 

I'd opt for this one myself. Either cut the rail for the square tube to go all the way through and use it as a double shear TC box. Or put a tube in it to hold your bolt. This would be the path I'd follow myself.

 

Cary

[JMortensen]

OK guys. I think I have a rough game plan. As always bounding ideas off of the hybridz crowd has been very helpful. Going to finish stitching the front frame and all that, then get into this project I think. It doesn't SOUND too hard... we'll see. I'll revive the thread when I have some pics of progress to show.