Structural Rigidity

Taranis · Feb 20, 2006

Hey all,
I have the interior gutted from my '69 and thought that might be a good time to think about some of the structural parts to the car. I'm going to use this car as a weekend warrior type deal with maybe a couple of pulls down the track.
I'm planning on a Keith Kraft 408 and an AOD or TKO (I haven't decided).

I have the 9" w/ 3.89 gears, Global west subframe connectors and CalTracs and I know to also put in an export brace and monte carlo bar.

My question is: Will my car benefit from a roll cage? And if so, what type of roll cage would benefit me the most while still allowing me (er... the kids) to use my back seat? Thanks in advance.

red65 · Feb 20, 2006

I was just thinking about the same thing for my '65, and actually decided against installing a roll bar, partially based on this posting at corner carvers:

http://forums.corner-carvers.com/showthread.php?t=14061&referrerid=0

While I spend some time at the track, most of my time is spent on the street. It seems that the general consensus is that a roll bar may actually compromise your safety on the street, while you're presumably not wearing a helmet, while improving it on the track where you're in more danger of turning over AND you're wearing a helmet.

In particular, I think there's some excellent advice in that linked thread:

DON'T put your kids in the back seat if you do decide to install your roll bar.

rbohm · Feb 20, 2006

yes, a rool bar will aid in structural rigidity, especially a weld in bar. as stated in the corner carvers thread though, roll bar padding isnt sufficient to protect the head without a helmet on. if you want a roll bar for competition, build a bolt in bar that meets class requirements, or eliminate the rear seating.

there are other things you can do to improve structural rigidity in you chassis though;

1: add stringers that run from the subframe connectors to the inner rocker panels. 1x2 steel tubing with a .120 wall thickness should do just fine as the runs are fairly short.

2: a center cage, ala' what tcp has, that connects the subframe connectors in the center of the vehicle will also aid rigidity. 2x2 .120 wall tubing will work here, or better in this case would be 2" round tubing.

Taranis · Feb 20, 2006

rbohm said:
1: add stringers that run from the subframe connectors to the inner rocker panels. 1x2 steel tubing with a .120 wall thickness should do just fine as the runs are fairly short.

Stringers? I've thought about running more metal from the subframe to the rocker panel before, but didn't know what they were called or if it would do any good. Are these run directly out from the subframes to the rocker panel?

rbohm said:
2: a center cage, ala' what tcp has, that connects the subframe connectors in the center of the vehicle will also aid rigidity. 2x2 .120 wall tubing will work here, or better in this case would be 2" round tubing.

How hard are these to fabricate?

Wow, that's a real good thread on Roll Bar Safety. I don't think I'll be putting one in. Numbers on the track isn't as imprtant to me as my child's safety and the enjoyment she'll (and I'll) get when we ride todether.

red65 · Feb 20, 2006

Taranis said:
I don't think I'll be putting one in. Numbers on the track isn't as imprtant to me as my child's safety and the enjoyment she'll (and I'll) get when we ride todether.

My thoughts exactly...

mustangdave · Feb 20, 2006

Good points I never thought about. The smaller area of the tubing would concentrate the impact to a small area and do alot of damage as opposed to the thin metal of the pillars or roof,but on the other hand, I have seen alot of caved in roofs and cars smashed to half their width.

gzminiz · Feb 20, 2006

I really would like to put one in abut I wouldn't want my kids to be in danger and I want the family to be able to cruise inthe stang. Now my question is. With 4 point harnesses wouldn't that make it impossible for a child or even an adult to rack the brain bucket against the bars? And the discussion on corner carvers i don't think takes into account old cars didn't have crumple zones, plastic interior and passenger safety things that they do nowadays. My67 has metal panels for the rear seat and the doors (mostly at least). If the roll bar is kept away from passengers and ALL passengers have 4 or 5 point harnesses I don't see how it is any more dangerous.

Ok, flame me like the did him and label me a child abusers and yadda yadda. But I am curious. I don't even have a child yet. I am trying to think ahead. I don't see any logical reason that a rollbar would cause people more harm if they are properly secured.

mustangdave · Feb 20, 2006

I'm not sure you could route the bar to be useful structurally where ones head could not impact it in the backseat. You could buy a frt. seat like Nascar but then you would have no side vision. You would need a spotter to go get beer.

gzminiz · Feb 20, 2006

I am not talking a full roll cage, just a roll bar. I am half looking for structural rigidity half just getting it to pass tech for drags if I run below a 11 (or 11.5 now i think, can't remember)

rbohm · Feb 20, 2006

Taranis said:
Stringers? I've thought about running more metal from the subframe to the rocker panel before, but didn't know what they were called or if it would do any good. Are these run directly out from the subframes to the rocker panel?

yes, these run from the subframes and subframe connectors to the rocker panels. you only need like 4 of them on each side. you can increase the stiffness even more by running diagonal braces between the stringers. it should look something like this;

l/l\l/l

the kenny brown extreme matrix brace for the fox body mustangs uses three stringers, and looks like this;

l/l\l

either way works well.

Taranis said:
How hard are these to fabricate?

the center cage is only a bit harder to fabricate than the stringers(lets call the stringers an extreme matrix brace for the sake of simplicity). basically your center cage will end up looking something like this;

\l/
/l\

the fun thing about the center cage is that you can easily add a driveshaft loop, as the cage should come together about 6-12" behind the front u-joint.

69Rcode_Mach1 · Feb 20, 2006

Also while you have that interior out this may be a good time to trim up that tranny tunnel so that you can fit a TKO into it. Makes things a lot easier when you aren't worried about blowing up your tranny.

Taranis · Feb 22, 2006

69Rcode_Mach1 said:
Also while you have that interior out this may be a good time to trim up that tranny tunnel so that you can fit a TKO into it. Makes things a lot easier when you aren't worried about blowing up your tranny.

Does the '69 tunnel have to be modified for the TKO? It seems that the majority of information I've read talks about 65-68 tunnel mods. How would you go about doing this? Especially since I don't have a spare TKO that I can fit in to make sure that everything fits.

RBOHM said:
the fun thing about the center cage is that you can easily add a driveshaft loop, as the cage should come together about 6-12" behind the front u-joint.

What's the point of a driftsahft loop? I'm not being difficult, I just don't know

rbohm · Feb 22, 2006

Taranis said:
What's the point of a driftsahft loop? I'm not being difficult, I just don't know

a driveshaft loop prevents the front of the driveshaft from hitting the ground and pole vaulting the car, or coming up through the floor pan in the passenger compartment should the front u-joint fail. it is a safety item required by race sanctioning bodies, and a very good idea on the street.

69Rcode_Mach1 · Feb 22, 2006

It is a pain to do and requires some good metal skills. You need to be able to cut and weld in a metal top on it to add. I am sure Bnickel will chime in I think that you can mess with the differentiial to get the correct angles. Ronstang has tried this in a 1969 and he said their is definite trimming necessary.

jbuening · Feb 22, 2006

There are quite a few people running TKO500/600 in 69/70 cars without tunnel mods. There are even a few running the T56 6speed in the same year cars without tunnel mods. If the driveline angle worries you, get angled shims that summitracing sells to change the driveline angle of the rear. Sure having the right drivline angle is great, but being off a few degrees will not affect anything. You don't think that buying 1" lowering leaf springs or blocks change your driveline angle a few degrees?

4MuscleMachines · Feb 22, 2006

Or you can get TCP's subframe connectors and add the x-brace. They now sell a driveshaft loop you can weld onto the x-brace.

69Rcode_Mach1 · Feb 22, 2006

Having your driveline angle off is going to cause, vibration, increased wear and tear, phasing, and lots of U-joint failures. It can be put in, but it is not the correct way to do it. I am merely pointing it out.

Taranis · Feb 23, 2006

So, if I don't modify the tranny tunnel, I have to modify my driveline angle which isn't the best thing to do.

As far as the driveshaft loop is concerned, I'll add it to my things to do. Since I have the Global West SCs, I'll have to fab up my own and I need to wait to do that until I have my tranny in.
too much to do....too much to do....

bnickel · Feb 24, 2006

69Rcode_Mach1 said:
It is a pain to do and requires some good metal skills. You need to be able to cut and weld in a metal top on it to add. I am sure Bnickel will chime in I think that you can mess with the differentiial to get the correct angles. Ronstang has tried this in a 1969 and he said their is definite trimming necessary.

like Buening said, you can get shims to correct the pinion angle which is the most crucial angle, yes the driveline angle will be off about 1-2 degrees but on a street car it will be fine, if you were running a full tilt racecar it would be a different story. for a mostly street car, as long as the pinion angle is within spec it will be fine.

jbuening · Feb 24, 2006

bnickel said:
like Buening said, you can get shims to correct the pinion angle which is the most crucial angle, yes the driveline angle will be off about 1-2 degrees but on a street car it will be fine, if you were running a full tilt racecar it would be a different story. for a mostly street car, as long as the pinion angle is within spec it will be fine.

What is your thought on this. Wouldn't 1" lowering leaf springs throw the pinion angle off too? Kinda like those trucks with lift kits. I can't imagine how far off their pinion angle is

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