Removing roof bracing and inner sheet metal, good or bad???

[jeffmerkur]

I was working on my car this weekend and got into a big debate with my buddy.

Its a 88 Thunderbird. I want to remove the roof bracing to get the cage higher in the car.

I was also going to remove the package tray and other secondary sheet metal after the "B" pillar.

My cage will be tied into the "A" and "B" pillar. He thinks I will be cutting all the strength out of the

Shell. My attitude is that the Cage becomes all the support the the shell needs and that sheet metal

Is just along for the ride at that point? Wanted to see what you guys think?

[99cobra2881]

I think you're both correct. Being a unibody the front subframe and the rear subframe are tied together with the roof structure. Remove this and you now have essentially a convertible with a roof. With the cage tied into the a & b pillar then to the rear subframe the cage will carry much of the load that the roof used to carry. The only problem here is that the purpose of the cage isn't supposed to be a structural member, the added rigidity from the installation of a roll cage is a by product of a well thought out cage.

 

Build it with driver safety in mind and you'll have nothing to worry about as far as the car flexing.

 

While you're at it installing the through the floor subframes I would recommend tack welding the floor pan. You could also possibly install a newer body mustang cross brace between the b pillar or bulk up what is already there.

 

Also on your cage I strongly recommend you add an additional down tube off the main hoop/door bars in both foot wells with an anchoring pad welded to the sheet metal. This will greatly increase the strength of the foot well and very well could save your feet in a crash.

[kbrew8991]

I've never seen someone complain that a production based car had too stiff a chassis. Too heavy maybe....

[Jeremymoen]

I gutted the inner sheet metal from the roof / sail panels in the Camaro. It already had a solid cage, so I figured there would be no issue. The body shell has not become flimsy or anything like I had heard it might. Seems to be a non-issue with a cage that ties in properly to the load bearing areas at front and rear. That's really the key. Make sure where the shocks bolt up / rear subframe / springs area is well supported. The cage will be WAY stiffer than the old unibody structure ever could be. Triangulation and tubing goes a long way. Cut a car in half and you'll see there's not much material really there compared to a well planned / executed cage.

 

I tried to envision the floor / subframe with no body around it, and make sure I felt like everything was triangulated sufficiently. Very scientific this procedure was. . . .

 

I would rather have the cage in first and cut the sheet metal later, to ensure the car doesn't have a chance to get twisted before the cage goes in. Sounds like that goes against what you are trying to do.

[jeffmerkur]

Thanks for the advise guys, exactly the kind of info I was looking for. I'm doing the through the floor subframe connectors first. I will remove enough of the roof bracing to get the main hoop in and then the front hoop. Tie those into the "A" and "B" pillar before removing the rest. A bigger pain but should keep anything from twisting.

 

My car does have a big cross brace that runs between the "B" pillars. Its where the floor flattens back out after it steps up for the back seat. I will post a pic. Fox stangs don't have this brace. I was thinking about setting the main hoop on top of the back seat step up because the cross brace is under it. This seems like it would be the strongest place to set it? Way stronger then the rear floor. This would tie the front and rear frame together after the cage is built.

 

The other thing I'm considering is removing the upper frame parts that run from the fire wall to the top of the shock towers( shotgun rails?). Then run tubes from the front hoop to the end of the front frame rails tying the top of the shock towers along the way. Taking the place of the shotgun rails.

[99cobra2881]

My car does have a big cross brace that runs between the "B" pillars. Its where the floor flattens back out after it steps up for the back seat. I will post a pic. Fox stangs don't have this brace. I was thinking about setting the main hoop on top of the back seat step up because the cross brace is under it. This seems like it would be the strongest place to set it? Way stronger then the rear floor. This would tie the front and rear frame together after the cage is built.

 

The other thing I'm considering is removing the upper frame parts that run from the fire wall to the top of the shock towers( shotgun rails?). Then run tubes from the front hoop to the end of the front frame rails tying the top of the shock towers along the way. Taking the place of the shotgun rails.

 

The b pillar floor crossmember is where the main hoop is on my race car. The sn95 mustangs had the b pillar brace added to them at the factory. Box the stock brace with the same plate your using for your other cage mounting points and you'll be in good shape. This also sets the cage further rearward and for me that made more room to set the seat back further.

 

If you haven't seen the cage building thread over at corner-carvers dot com it's worth a look, lots of pictures and a lot of how not to build a cage.

 

Be careful removing material from between the firewall and the strut towers, that's one place AI rules are very particular, check with your regional AI director before breaking out the sawzall.