I know that the FB chassis is already stiff for the time that it was produced, but i'm looking for a way to stop the creaks and groans that i hear everytime i go slowly over speed bumps or pull into/out of driveways. the groaning is coming from the rear of my car. I have the Racing Beat 3 point strut tower bar. I'm planning on seam welding my chassis after I fix all of my rust (it's confined to drivers floor pan and the passenger rear wheel well, just a tiny hole about 1/4" square), but for the time being can I do anything to stiffen my chassis? Right now i'm thinking about rivoting the seams to make them seem as one. If i go this route, i'm going to use 3/16" Aluminum pop rivots, the same rivots that i am using to cover the factory drain holes in the driver and passenger floor pans, sealing them with 100% Silicone Caulk, clear in color, paint under it with Rustolem Flat Black, and then use some black rubberized undercoater.

Would this stiffen the chassis enough to justify the work, or am I just wasting my time? Is the Aluminum going to be strong enough to not shear under the stress of the chassis flexing and the seams shifting?

 

good question

 

The squeaks/groans might be coming from worn bushings, not the unibody itself...

 

that thought had crossed my mind, but it only squeaks and groans when the unibody itself is under alot of load going into/out of driveways or over speed bumps. the suspension is completely quiet.

 

no they will not.

-billy

 

thanks. will it be worthwile if I use some bigger Stainless Steel rivots?

 

Not if you're going to seam weld later. Instead of seam welding have you looked into using the 2 part foam in the rockers and strut tower horns and anyplace the body panels are joined to make a tube? Or, do a combination of seam welding and foam.

 

dont people just use the rivets to keep the chassis from warping when they seam weld it? and maybe give it some extra strength, i would use stainless. but i know that using rivets is supposed to be the "correct way of doing it" if there is such a thing as a corect way. but do some research,

but seeing as nobody has ever posted a thread saying "help sqeaking chassis need to strengthen" i would try looking for other sources of the sqeak, probably your rearend bushings or maybe even your exhoust,

-Paul

 

I welded in a 6 point roll bar and foamed the cavities. I still have squeaks. Most of which are interior panels and the heim joints in the adjustable rear sway bar.

 

if you use alot of rivets i dont think the aluminium would shear. the stress would be spread out over many of them.


Ive never heard or thought of riviting the seams though.

do people do this?

 

i've heard of people rivoting and welding seams for Time Attack cars in Japan. I just wanted to reduce the squeaks until I can learn to weld and seam weld my car.

 

this is a cool and easy idea anyone can do.
ill check more into it and post back what i find out.

 

nah its not a great idea. specially if your talking about pop rivets.

 

Considering I remove my rear sway bar to increase handling, I dont see how you would need anymore stiffening.


If you welded your car, it would still squeak and groan. I'd be after the bushings before I went crazy on stiffening.

 

the sway bars have nothing to do with chassis rigidity.

 

Alak is talking a chassis tuneability, which is the whole reason to make it stiff. If your chassis responds well to suspension adjustments, then you don't need to stiffen it and you should just figure out where the squeaks are coming from and deal with them.

To illustrate what I am talking about, you are tuning the handling on an understeering, front heavy car. If you make LARGE increases in rear sway bar stiffness without increasing oversteer, then your chassis may be flexing too much to be able to properly transfer weight from the front to the rear.

I recommend buying and reading Race Car Vehicle Dynamics, by William and Doug Milliken. It is absolutly the bible of racecar handling dynamics for racecar engineers thoughout the world. If you were in Formula SAE then you know what I'm talking about.

Matt

 

the rear suspensions functionality with or without a swaybar doesnt have much to do with the chassis.

there are other ISSUES with our rear suspension and removing the sway bar is a bandaid that reduces over steer and causes other handling problems.

i will agree that for a street car a welded chassis is probably way over kill on an rx7

 

matgls23 - Umm, the sway bar has no effect on weight transfer from back to front. And 7s typically oversteer, rather than understeer. Not sure if I'm misunderstanding you or if you are mistyping, but the information that you are attempting to provide seems to be loaded with fecal matter (no offense).