Subframe connectors - what would you do different next time?

[heavy85]

I'm in desperate need to replace my framerails. Unfortuneately not from rust as there is none but because they have been jacked on in all the wrong places about a bazillion times and as a result the front end sags when I put it on jackstands - it's a 240 with the short rails. So I've looked at and read about all the various methods (Jeronimo's u-channel, Baddog, Pete's recessed into the floor, etc) and am pondering which is the best method to go. So of those that have been there and done it before any advice and what you would do differently next time?

 

Thanks

Cameron

[BWRex]

I did Pete's style,and IMO,they look the toughest,I fabbed my rollcage main bar pads to them(rigid),you can use them to mount new fuel/brake lines to the sides of them(underside,which I'm planning to do),just an all around strong,thought out way to add strength and to tie the front and the rear together.A little added weight,yes.But added safety,yes.Thoughts on torque frame twist,gone.It's a big project,but in the long run,I'm certain you'll be glad you made this part of the Z as strong as possible.IMO,of course.I'd like to see some more posts on this topic,esp.from people who came up with their own ideas,and/or added or deviated from this premise.

[Mikelly]

I've helped build Pete's style and have them in my personal project car right now... I've also got a set of BadDog rails on hand as well... I can tell you that if you don't want to go the complex route of Pete's, which are the strongest, but also the most involved, You can't go wrong using the BadDog rails... They are well made and very strong when installed properly.

 

Mike Kelly

[JMortensen]

I think some of that sag that you're seeing comes from the front frame rails and the rad core support. One of my issues was when I'd set the car on jack stands at the TC rods, the front of the frame would sag and creak and groan when I let the jack down. I don't think it was my mind playing tricks, but I swear I could SEE it on my car. Set it down on the TC buckets and you could watch the front end sag 1/4" or so.

 

I used the Bad Dog rails, I'd do it again, they fit into my project great, but I don't think they would cure the problem. You're looking at strengthening the front frame rails in addition to the SFCs to get rid of all the looseness in the front end IMO. The stock rails are pretty thin and flexy, so you're either talking about a lot of bracing, or replacing the rails with somthing more substantial. I went with bracing, and I think what I ended up with will be fairly stout. Pete went with new stiffer rails, 2 x 2.5 x .093. Regardless of which way you go, I just wouldn't count on SFCs to do the whole job. I think you'll be disappointed if you do, especially since you autox. I had a triangulated strut tower bar and I still tore up a couple of brass radiators because of the flex in the front end. That says something about the frame flex. Just look at the structure up front though. There are UPPER frame rails too, and the uppers take a lot of load from the strut towers (since you're turning a lot this is more important than the engine torque). My plan is to make an X that ties uppers and lowers together, and hopefully that and the other bracing I've installed will keep the 4 long rails in front from moving around too much.

 

I haven't tested my structure since I've added any the stuff that I've done. There are relatively easy ways to do so and it probably would have been a good idea. But it's kind of hard to do on a rotisserie, so I'm just trying to go extreme enough and hoping that it will turn out satisfactory when I finally get behind the wheel again.

[heavy85]

BWRex and Mikelly - I've wondered how Pete's design affects your feet and using the pedals with the hump in the middle - what's your guy's experience? Also, did his dimensions work exactly as printed or due to tolerances of different cars did you have to tweak them a lot to fit?

 

I think some of that sag that you're seeing comes from the front frame rails and the rad core support. One of my issues was when I'd set the car on jack stands at the TC rods, the front of the frame would sag and creak and groan when I let the jack down. I don't think it was my mind playing tricks, but I swear I could SEE it on my car. Set it down on the TC buckets and you could watch the front end sag 1/4" or so.

 

Mine is actually fine if I set it down on the TC buckets. It's when I sit it down with jackstands placed under the rails at the base of the firewall the front end sags to the point the doors no longer close. This is why I think it's the rails. The SFC are just part of a strut bar / roll-bar (no cage for head clearance / safety reasons) system so I think in the end it will be a fairly stiff and safe package.

 

Any others like to comment?

 

Thanks

Cameron

[BWRex]

In reguards to the front,I strengthened the swaybar mounts(there's a good thread on swaybar reinforcement:search: )and I'm going to fab some strut tower braces once I test fit the 350TPI setup I've got going in.Hopefully a triangluated setup attaching to the firewall as well.That should stiffen up the front well.

I used 2x3 .125 tubing for the SFC and the inside hump is about 1/2"of that.I was thinking the same about foot placement,but w/insulation and carpeting,you'll barely notice it.Plus,it actually fits your foot pretty good.Here's a pic.passenger side.

The under side hangs about 1 1/2" below the floor,and will be perfect for running the brake/fuel lines to the sides too,as stated above.

heres a pic of the main rollbar perch behind the passenger seat.I welded it to the SFC,top of the rear main frame,and boxed it in below.Should work out awesome.Hope these help!

[BWRex]

I didn't realize how small those photos are!I'll have to figure that out.Members galleries have full size ones.Good luck with the project!

[BWRex]

BWRex and Mikelly - I've wondered how Pete's design affects your feet and using the pedals with the hump in the middle - what's your guy's experience? Also, did his dimensions work exactly as printed or due to tolerances of different cars did you have to tweak them a lot to fit?

 

 

 

I bought the steel stock,used his basic premise,took a million measurements,and custom cut my own angles and mounting points to fit.I'm sure Pete's angles are right there,but some people like to do it the hard way.....

[Mikelly]

I had no issues with the framerail interfering with your feet. If done properly, the rail is not far into the interior of the car at all, and if covered with carpet, you won't notice it at all...

 

Mike

[rags]

Just to throw another option in the mix, I have my additional metal inside the rocker boxes. I cut off the rockers and welded 2x3 box tube to the inside rocker panel. Its the panel that has all of the 2 inch holes in it along the foot well. In the front the box tube is tied into a 2 inch diameter tube that is tied to the TC cup. Out back at the end of the rocker panel, I have a 1.5 inch tube that ties the rocker box to the roll bar. I'm sorry I don't have any pictures as this was done about 16 years ago. So far so good and with about 3/4" of bondo in the roof (don't ask) there is still no signs of stress cracking.

 

Has anyone seen the braces that used to be available that would tie the TC cups to the front crossmember? I used to have a set way back when and can't seem to find them and I don't recall ever seeing them mentioned on HybridZ.

 

Joe

[heavy85]

OK so I did a little math today and this is what I came up with. Keep in mind that A (area) is proportional to weight - lower is better, and I (moment of inertia) is proportional to stiffness - higher is better. Then the ration of I/A is an indication of the efficiency of the design - higher is better. I'm assuming that the SFC will be bending vertically. Also, if I measure my beat to hell frame rails they are about 2.5" wide and roughly 9/16" tall.

 

(EDIT: the formating of the table below does not come through so you'll have to interpret)

 

Tubing size (w x h x t) A I I/A

2.5x1.5x0.12 0.90 0.325 0.36

3x2x0.12 1.14 0.743 0.65

3x2x0.083 0.80 0.541 0.67

2.5x2.5x0.083 0.80 0.779 0.97

 

So obviously of these choices the best (most stiffness for the least weight) answer would be 2.5x2.5x0.083 tubing for the SFC - same weight as the standard 2x3 design but 44% stiffer. Given that the factory rails only stick down roughly 9/16" I dont think I want the new ones more than one inch below the floor. That would leave 1.5" stick above where your feet are. Above everyone said that 1" isn't bad but I wonder about 1.5"? I'll have to tape a board to the floor and see what it's like. Any other thoughts on this?

 

Thanks

Cameron

[Dat260]

Hi,

I have the same problem as jmortensen, my front end sag when I put it on a lift. I like Mull's aproach on his video #13, it looks like it would be strong enough not to sag plus add a triagular bar joining the two towers to the firewall. I do not like the idea of having the floor rail protruding even a 1/4". That area should be flat. I see it as a safety issue in terms of reaching the brake and/or clutch pedal.

Ari

[ron adams]

My frame rails were an ugly mess (Northern Rust). I used 2.5" box tubing and it fit right in place. It is clean and strong. Plus you can use a jack at any place along them you want.

[JMortensen]

I wish I had thought of strengthening the rockers before I welded in my roll bar. In retrospect I think the rockers are more important than the SFCs. Just think, with the rocker design, Nissan put full tubular frames down both sides of the car and they attach in right at major structural spots in the front and rear. They stopped the floor rail before it got connected to the rear. It's obvious which one they thought was more important.

 

2.5" tubing on the SFCs is major overkill IMO. Good for front frame rails. Way overkill on the SFCs.

[BWRex]

I wish I had thought of strengthening the rockers before I welded in my roll bar. In retrospect I think the rockers are more important than the SFCs. Just think, with the rocker design, Nissan put full tubular frames down both sides of the car and they attach in right at major structural spots in the front and rear. They stopped the floor rail before it got connected to the rear. It's obvious which one they thought was more important.

 

I was going to attach my doorbars from the main hoop,to the pads by your feet,and also weld these doorbars to the front interior sides of the inside rockers,instead of to just the floor pads.Should make this section stronger.I agree with the above,I wonder if they were trying to conserve on steel,or if the rockers absorb 90%of the flex.I know people here have welded tubular bars between the inner and outer rocker panels,but in terms of photos,haven't found any.I do think Pete's style helps with structural integrity,but I would like some more info or a link on the rocker method.....

[JMortensen]

I was going to attach my doorbars from the main hoop,to the pads by your feet,and also weld these doorbars to the front interior sides of the inside rockers,instead of to just the floor pads.Should make this section stronger.I agree with the above,I wonder if they were trying to conserve on steel,or if the rockers absorb 90%of the flex.I know people here have welded tubular bars between the inner and outer rocker panels,but in terms of photos,haven't found any.I do think Pete's style helps with structural integrity,but I would like some more info or a link on the rocker method.....

I did my rollbar similarly where it attaches to the rockers instead of a box on the floor (see pics). If I end up going with the full cage, my thought was to put in a "door bar" that is right on top of the rocker, and then attach with gussets to the rocker all the way down it's length. I think attaching the cage to the rockers gives the cage a better, stronger attachment point, but I don't know how much it does to strengthen the rocker.

 

[JIM73240Z]

what if you were to put a 1x3 on edge down the rockers and attach the hoops to that. kind of a cage that is independent of the car but attached to it, i guess. hell i dunno. just thinking out loud, or in cyber. my thought is to put the cage on good fresh metal and attach the seats to it as well so that in the event of something not very nice, you are inside of a cacoon(sp), almost military in thought and redundancy.

 

jim

[tube80z]

.I know people here have welded tubular bars between the inner and outer rocker panels,but in terms of photos,haven't found any.I do think Pete's style helps with structural integrity,but I would like some more info or a link on the rocker method.....

 

You mean like this?

[BWRex]

JMortensen,I like that idea,I noticed 240Hoke 'grooved' the front rear wheelwell to possibly add strength to the mainbar.I like how the mainbar is 1/2 'sunk' into the rocker.I wanted my mainbar pad to tie in the SFC,rear frame,and rocker and box in from underneath.Does your pad tie into the perpendicular rear frame?BTW,What dia. is your mainbar?Thickness?

 

Tube,Did you fab box steel to the inner rocker?Along the lines of what I was thinking.I'm digging that idea,so post a couple more photos if you have them of front and rear mounting,steel thickness,etc....

[BillZ260]

All I can is that if you want 4 great spots for your Z to sit on jackstand for years at a time with no issues w/ frame or body tweaking....Do Pete's set up.