Frame damage and frame strengthening

[240Dave]

Two part question: Frame damage and frame strengthening.

Obviously when looking for a daily driver one wouldn’t want to put in the work to repair much more than a dented fender or cracked bumper. But if you’re shopping for a project car, should one with "frame damage" be immediately dismissed?
The answer I always get is a big YES. But why? And what part do you call the frame when considering what is frame and what is body damage.


What does a frame really do for you?

Your rear suspension connects to the rear sub-frame, so if this is damaged, it is understandable that your car won’t handle right. But since the rear sub-frame is bolted, (not welded) on, it can be replaced without much trouble. I can’t picture what the rear sub-frame is bolted to, but it doesn’t appear to connect to the frame rails in any way.

The front sub-frame/cross-member holds the engine and front suspension and seems to be extremely strong, just like the rear sub-frame; Replaceable if damaged.

Then you have the lowest and outermost part of the car under the doors. Now to me, (looking at the rear of a front clip) this seems to be what really holds the shape of the car.

Finally, the frame rails. Now, these pieces, generally regarded with the highest importance, just seem worthless to me. Extremely thin metal just attached to the underside floor of the car. It eventually turns upward towards the front and becomes a solid place for the front sub-frame and shock towers to mount to. I've seen new/stronger framerails for sale for other cars.

Other bits would be the upper framing from the firewall to the front of the car at about the height of the top of the shock tower. The horizontal pieces above and below the radiator. And, of course, the rest of the cars framimg that the sheet metal is attached to.

The goal for any car would be to have a frame that doesn’t twist and flex under cornering and engine torque; causing suspension geometry changes. So what parts are responsible for this and which ones aren’t so much? Why are some considered irreplaceable (frame rails) while others (like the outermost part beneath the door) are just cut out and replaced with undamaged pieces.



I saw, in another post, the mention of a cage that goes through the firewall and mount to the shock towers. Say you install an 8 or 10 point cage that goes from the front shock towers to the rear.

• Main hoop behind the driver with rear supports going down to the rear shock towers
• A bar horizontal welded in between the rear shock towers
• A horizontal bar at the base and in the middle of the main hoop.
• Diagonal bar from the top of the main hoop to the bottom
• Forward bar from the top of the main hoop, lining the roof, going down the a-pillar and down to the floor
• Horizontal bar at the top of the forward bars at the top of the windshield
• Door bars in an X shape from the main hoop to the vertical part of the forward bars
• And finally bars going from the forward bars, through the firewall, and welded onto the front shock towers
• Adding gussets where necessary
  
• Then some form of bolt-on front strut tower brace from one to the other and triangulated into the firewall and/or the front frame-like piece above the radiator

I think it is safe to say, you would have no chassis flex in a car equipped with such a cage. Now after that, how important would the stock frame be? If someone put their bottle jack through the frame rail, who cares right?

Ok, so say you can’t or don’t want to go that wild. Other than strut tower braces, what are some ways to stiffen a cars chassis and let your expensive suspension do it's work? I’ve heard about foam injection…



NOTE: This is just a general post, I’m not implying that I will be doing anything mentioned...So don’t ask why the heck I’d want to put a 37 ½ point roll cage in my street car(dare me to? hehe). Just trying to get an understanding of everything in order to help me build a solid toy, and possibly make this thread (after you all add what you know) a good resource on this stuff.

[Bill Roberts]

Damn dude, I saw your topic and thought I would chime in here...but after reading all that...I will say only the basics that hold true.

1. When metal is bent, it is weakened.
2. As long as all 4 corners "trace" properly, Height, scew, track, caster...and it can be alighned perfectly, then your only concern is fatique. The frame may need some bracing.
3. Body parts fit correctly.
4. All driveline parts fit properly, not binding.

Most frame problems are body/suspention and not driveline.

You most likely answered your own questions. I just added the basics that frame straitening folks go by. Build and wreck a few dirt track cutlasses and get them back to racing condition driveability wise and you quickly learn where to add stress points to help the welds, the pulls and the kinks. Personally, as long as the car looks good, goes down the road strait without abnormal tire wear, fits nice, drives nice and has been reinforced to a shade beyond factory strength....no problem at all.


To sell a car with a known bent frame and not disclose it, even after repair is a no-no IMHO. This is the only REAL concern.

[pr240sx]

About front towers cracking?

How do you repair, prevent this from happening?

As for reinforcing the frame rails, you can use the foam injection thing that 300zx owners loove to do.

[240Dave]

I've never heard of them cracking, but I have heard of the shock towers actually being ripped off the frame
I think anything you can to do keep those towers from moving in relation to each other (what the whole post is about really) would prevent it from happening.
As for fixing it...I don't know other than just welding it back assuming it's not bent permanently.

I'm surprised there haven’t been more people posting on this having been up for a whole day already. I'd think most everybody with a strut tower brace or other frame strengthening bit would chime in...

I guess my posts are too long

[Var]

Originally posted by pr240sx
About front towers cracking?

How do you repair, prevent this from happening?

As for reinforcing the frame rails, you can use the foam injection thing that 300zx owners loove to do.

what the hell is this foam injection talk about? can someone link me to some info, pricing specs or anything. You got me interested. I already ordered an autopower roll cage, would the foam injection help further or would it be beating a dead hooker?

[240Dave]

Originally posted by westboroughpimp
...would the foam injection help further or would it be beating a dead hooker?

Thats what I'm wondering...

http://www.itwfoamseal.com/auto_aftermarket.htm

[Var]

Originally posted by 240Dave
Thats what I'm wondering...

http://www.itwfoamseal.com/auto_aftermarket.htm

found a more informative link..read the last article on this page..i think i might try this out after the roll cage is in.

http://www.sportcompactcarweb.com/pr...0zx/index.html

[isimon91]

its a long bump, but i searched and didnt find much on this topic.

can the frame of a non-rusty car be filled and strengthened easily with this stuff, or would you have to do the entire chassis to make it effective?

[schells86]

i was always wondering this too. Nissan used such thin metal when making those "frame rails".. how much of a difference could they really make if they were rotted or not.

[redline240sx]

For the frame rails "xcessive manufacturing" fabricated replacements so you can just cut and weld them in.
For frame straighten, if the car had ben in an accident and the frame bend badly, i dont think its worth fixing because metal can never be straight after bent..
As for the foam and what I know about it, is that it reduce the amount of vibration in the car and makes the frame a bit stiffer....

Just my $.02

[J~TIN]

has anyone ever used this foam shit?

[Bluejayde]

Looks like the pics are broken but here ya go-

http://forums.freshalloy.com/showthread.php?t=162693