Rear quarter panel buckle

K

karolko

Well-Known Member
Joined
Sep 18, 2007
I was wondering if anyone knows exactly why the rear quarter panels buckle on some peoples cars after doing a frame notch.

Also what are things that people do to prevent this from happening.

What i would like to do is notch the frame and possibly get away with not having to put in a cage, i understand that the cage will solidify the entire structure, but are the other alternatives,

What about those guys runnign witha crossbar behind the axle???

Photos would be cool as well.

Thanks
 
Because they weren't done right. Maybe too much power? If that's the case it should have had a cage anyways.
Mizzi did mine and they were very solid, incredible welds, no flex, no bs with drag radials I never had any issues.
 
Thank gnxtc2, i believe i have read this thread before.

in the thread, they mentioned welding plate to the backside of the framerail beofre cutting. Did they the entire area that ws being cut, or did they just plate the front and back portions and left the middle hump over the axles alone.

could someone post pics of the bracing at the back of the frame rail, and photos of the location of the crossbar.

i understand that there are alot of guys with a cage and a frame notch, but how many boys are out there that are only notched, who launch hard and do not buckle??? I think i would kill myself if i went to the track and buckled the quarters...
 
every time I..

see a post on frame notching, and the suggestions for added reinforcement, I start to chuckle...
Seems the local moron, did his own notch, ALL the way back to the inner wall of the frame.:eek:
He then proceeded to do banzai launches, trying to get the POS to run the current TSM times...[He was the guy that said he'd be running 150 that yr, at BG!]:rolleyes: Whoops! Sumptin wong!!! The frame bent, & qtrs buckled so bad, that the car was JUNK!:eek:
I did mine after I put the bar in.[And, new body bushings] I levelled the car on stands, at the tires. I then used 2 pcs of scrap angle iron for support columns. I put them at the far rear of the frame, and tack welded them on. Then, I did the cutting/welding, using the piece I cut out, as the outer plate. Only by seeing the end areas of the cutouts, could 1 see that the frame was modded....[Still had the white plastic discs in place]. Worked for me.

Bottom line: Do it right the first time, and avoid the body shop!
 
Chuck, here s our wuote from the other post:
"FIRST thing I do is to raise the car, and block to square, with stands at the wheels, to simulate loading as seen on the ground.
Once in position, I tack a strut of scrap tubing/angle iron, etc, from the floor to the very rear of each rail. This supports the rear portion of the frame. I clean the insides of the rails, and add the "fish plate", before cutting the outers off. The plates are 1/8" MS, and are rounded on the ends, so as to not create stress risers, resulting from welds all the way to the edges of the rails. [Square corners also create risers.] I also add about 6 plug welds, so I don't have to weld 100% of the perimeter. I then cut the outer 1/2 of the rails just to the inside of the overlap joint. The piece that remains inside the frame can be knocked out, the cut cleaned up, and the outer shell slid back into the inner 1/2 and tack welded in place. I then do the other side, and once done, I alternate sides, so I don't pour a ton of heat into the rails, while finish welding.
NE1 that thinks this mod is a "lead pipe cinch", may not have seen what can happen w/ a botched job!!
We have a local, [resident moron], that did the hack job...1 good banzai launch, and the qtrs folded so bad, that the car was JUNK!!
Another "checkpoint".. BE SURE the body mounts are fresh, and the body, and rear axle are as square with the frame as possible. "

I like your explaination of the job, but it is still vague to me where you put your fish plate on the frame rails? I like you idea of tacking in the rear rails to the ground.
 
The reason the quaters are buckling is due to the rear lower front frame control arm mounts twisting upwards into the floorboards. Yes, the floorboards will also buckle. You have to minimize the control arms from twisting.

IMHO adding a steel plate on the inside of the frame rail will do nothing. Take a look at Rick Jensen's car launching in the second to last issue of GM High Tech Magazine. That car has a major quaterpanel buckle on launch. There is also a write up on frame notching in a past issue. I don't know if Rick's car has a cage.

When I did my notching, I added vertical supports inside the frame. When I get home, I'll post a pic. Got to remember, the factory did not design the frame to withstand hard/violent launches. The frame is designed to give a confortable ride while maintaining its intergrity.

I have a cage in my car along with some added bracing. I also have HR Parts & Stuff lower control arm front frame re-enforcements. My cage is welded to the frame above the lower control frame mounts and my rear down bars are welded to the top of the coil spring mount. You can see the rest of the bracing.

Billy T.
gnxtc2@aol.com
 
Here are the vertical supports inside the frame rail. I made the notch bigger/longer to fit a larger diameter tire than what is pictured.

P1020029.jpg


P1020030.jpg


Billy T.
gnxtc2@aol.com
 
Very nice, gnztc2

this is what i call proper wormanship! and from a structural standpoint, i can see how it is much stronger than others without the vertical supports.

Would you happen to have photos of how you guseted you control arm mounts. You also mentioned that you also have other bracing... lets see that too.
 
Hi,
It is interesting to hear you guys talk about the fast end of things, but do you know that this problem happens on street cars too? Mine is not particularly fast, nor has it been harshly used, but the right rear quarter below the opera window is wavy,obviously a stress wave. A generic problem, dealing with the body's support by the frame, in my opinion. Maybe that Bushing kit would help me, I don't know.
 
I have engineered many back halfed cars and also cut a few for just tire clearance. These cars are a different breed. Most cars, in order to get any traction end up with ladder bars or 4 link. It is new to me that these go this fast on modified factory set-ups. In my expierence, whenever you remove metal from one side of the frame, you must reinforce the opposite side. You may get away with not doing so, but each guy here is running a different combo and could be 100 or more ponies than the other fella. Therefore buckling may happen to one , but not the other. I have used a different approach for finding more tire clearance and it is very strong also. I have not done a turbo car , but a 600 horse 55 chevy mini tubbed, no cage. It was able to stand up to massive launches with transbrake at about 4500-4700 rpm's. I think it would work on these cars also, but I have no intention on doing it to mine, so I will never know. If anybody wants to gander at it they are welcome. It is a little easier to install, but I have not researched all that may need to be done. It may interfere with tailpipes a little. I do not believe so, but modification and fabrication are part of our hobby. This is just an opinion and I am not saying anything bad or nothing like that. I just saw a picture of a notched frame and "cringed", not much strength left. I was a design engineer in a tool and mold shop and a journeyman moldmaker for 17 years.

Thanks,
Coach
 
These are the HR Parts and Stuff re-enforcement brackets.
P1080065-1.jpg


If you look closely, I made triangular pieces to support the upper control bracket/mounts.
P1080056.jpg


If you go into the link below my Sig, there are more photos.

Billy T.
gnxtc2@aol.com
 
Hi,
Very funny! What's wrong with a simple brace package like the GNX used? I guess I'm hanging with the wrong crowd. Your cars are cool, though.Have fun!
 
Follow the link in my signature. I put a rear driveshaft loop between the lower control arm mounts and ran 2 diagonals from the loop up to the upper control arm mount box. I also have a bar going from the rear roll cage tubes all the way to the end of the frame rails. I did not put any reinforcements on the inside of the frame rails. After many 1.28 to 1.32 60 foot times no buckled quarters or cracked b pillars. You could do this just as effectively on a car without a roll bar.
 
You re-enforced the lower control frame mounts also. IMHO, this has alot to do with the quater panel buckling.

Billy T.
gnxtc2@aol.com
 
gnxtc2, and steve hughes, thank you very much for posting this information. i really like how you gusseted the control arm brackets.

as for the crossbrace (which is also your driveshaft hoop), i have seen two different setup idea when putting in a cross brace: some guys have put in a cross brace behind the axle, simply connecting the two frame rails together, and now this one. i am trying to wrap my head around where the stress will be going and how the frame will be reacting to it.

do you guys think that both are nessasary? none, one???

Also GNXtc2, you mentioned body mounts... following up on that idea, wouldn't you want body mounts that are soft and can absorb some of the flex that might be given off from the frame and into the body? so for example, run factory rubber and not polyurathane body mounts? does this make sense, or am i off my rocker?

Also, gnxtc2, why didn't you box in the gusseting for the upper control arm braces like you did the lowers???
 
My reply was for a non-caged car only. Basically for street use, it would work on race also. Steve or gnxtc2, would those control arm braces work to limit this on a street car? They are a bolt on app. I do not plan on cutting anything on a 18k mile GN, but do plan on a low11/high10 combo.

Thanks
Coach
 
with respect to cage's, wouldn't it be better to bring the backbar all the way back to the rear of the frame, and not to the upper spring perch?? Straight tubing is stronger than bent tubing, and i would think that trianulating a larger area would better?

What do you think about that?
 
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