[unclescratch]

My '65 A-body has very noticeable cracks in the body coming from the corners of the rear window. The book; "Doorslammers - A Chassis Book" has a picture of this exact condition, saying it results from chassis flex. My GTO is driven about 4000 miles during 6 summer months of each year, most all street, once in a while the 1/4 mile. (2.14 60' 13.70@102 4200 ft. altitude) The fix is described in the book as a multi-point roll cage. I'm not too comfortable with the thought that I'm 'beating-up' my car when exercising it, and I'm not fixin to cut it up for a roll bar. Have considered boxing the frame inside the rocker panel area like the ragtop cars and/or solid body mount bushings. But I don't want to eliminate the 'very good' ride quality that this car has. And I don't know if these two ideas would help at all. Since I'm doing a repaint, now is the time to address some of the problems I have found with the body. Maybe these cracks took a long time to show up? Any thoughts on this??

[unclescratch]

My '65 A-body has very noticeable cracks in the body coming from the corners of the rear window. The book; "Doorslammers - A Chassis Book" has a picture of this exact condition, saying it results from chassis flex. My GTO is driven about 4000 miles during 6 summer months of each year, most all street, once in a while the 1/4 mile. (2.14 60' 13.70@102 4200 ft. altitude) The fix is described in the book as a multi-point roll cage. I'm not too comfortable with the thought that I'm 'beating-up' my car when exercising it, and I'm not fixin to cut it up for a roll bar. Have considered boxing the frame inside the rocker panel area like the ragtop cars and/or solid body mount bushings. But I don't want to eliminate the 'very good' ride quality that this car has. And I don't know if these two ideas would help at all. Since I'm doing a repaint, now is the time to address some of the problems I have found with the body. Maybe these cracks took a long time to show up? Any thoughts on this??

[mike nixon]

i'm going to copy this topic to the street and body shop forums.

there may be some good advice for you there in reagards to stopping the progression of the cracks.

mike

[fast1970transam]

what kind of body bushings do you have?

She got on Payless, me I got on gator shoes

[fast1970transam]

with solid bushings and good suspension you wont be able to tell a difference

She got on Payless, me I got on gator shoes

[unclescratch]

With the exception of the ones I replaced when I installed new trunk floor panels, all the bushings are the ones that came with the car from the factory. The trunk bushings are rubber.

[fast1970transam]

I had some cracks from body flex. i changed the bushings and the ride did get better ,but i never fixed the body flex cracks. poly or solid should work fine. i used poly,but now i'm doing solid

She got on Payless, me I got on gator shoes

[cscottfergus]

I think a way to stop the crack is to drill a hole at the end of it (not where it started ) so it cannot progress any further. Consult a body professional.

Buick Grand Nationals had the same problem cracks due to flexing wit T-top cars. Not sure of fix.

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1967 Firebird 400 conv T400 3.08, 1989 Formula 350 700r4 3.27

[cscottfergus]

Have you thought about putting an airbag inside the right rear coil spring? This should help limit the tendency to squat on that side(assuming you have a problem with that).
How about aluminum frame mounting bushings for the body(might hurt ride quality) will limit flex.

Contact Ken Crocie of this list former owner of HO specialties. He may know.

also found this Oldsmobile link that talks about A bodies. It is crazy long but had lots of useful info on suspensions

http://www.442.com/oldsfaq/ofsus.htm
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1967 Firebird 400 conv T400 3.08, 1989 Formula 350 700r4 3.27

[This message was edited by cscottfergus on September 03, 2003 at 12:49 AM.]

[GoatRider]

I would think that using solid body mount bushings (without also having a roll cage) would actually make your body flex / cracking problem WORSE!

By making a solid connection between the body and the frame, you are using the body shell as part of the structural strength of the vehicle.

I would think you actually want some nice new and super "soft and spongy" body bushings so that the body is "floating" on top of the frame and not experiencing any of the twisting forces that the frame goes thru during those high torque launches.

Anybody who knows this for sure please feel free to correct me if I am wrong here.

Good luck.

"Nothing Beats an Ol' Goat..."

[cscottfergus]

Thank yo for addressing that point.
Get expert advice about the aluminum bushings. I don't have firsthand knowledge. But it is an idea that you can research. The bushings would sure flex less, but what it might do to the body is beyond me. That Oldsmobile link I posted had the idea and discussed it. Maybe you can contact them and find out who the experts are.

Here is some info from that Olds site. This Olds 442 site is very useful. Once again use it for ideas anf get expert opinions.

"
Stiffening Chassis
While I can't give you any resonance numbers, I can tell you what I've seen work and some discussions I've had with Ken Snyder on making a competent handling A body for SCCA type racing. The most important thing is to eliminate the C channel in the center of the frame. This is what allows most of the flex. While it would stand to reason that the body of the car would make up for this section directly under it, keep in mind that the C channel starts right under the front edge of the doors.

Between that point and the front of the body section there is only one body mount per side. This ends up acting as a pivot point, and allows the C channel to flex with resulting movement seen in the very front of the car. While poly body bushing would help, you are still only relying on the front fenders to reinforce the front section of the frame to make up for the C channel. The solutions we came up with for stiffening up the structure was to first box the C channel (though with the recent talk of convertible frames, this seems like a more elegant and factory looking solution).

The next step would be poly body bushings. The final amount of stiffening would need to be something along the lines of running tubing from the firewall to the core support. With a bit of work I believe that these could be run under the fenders and be near invisible. The result would solve all of the identified chassis stiffness problems with minimal cost and without making major modifications to the vehicle. This would also give you the solid foundation you would need to do some real suspension tuning.

[ Thanks to Mike Bloomer for this information. ]

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1967 Firebird 400 conv T400 3.08, 1989 Formula 350 700r4 3.27

[This message was edited by cscottfergus on September 04, 2003 at 02:48 AM.]

[KEN CROCIE]

Goatrider got it right. The std. frame is very flexible.stiffening the bushings only puts more stress on the body.Closing the open c section of the frame might help,but I have not tried this.The olds guys are correct if you want to ignore stress crack problems of using the body as a frame stiffener.Try putting some platiciser in the next paint job and/or learn to live with it.

[cscottfergus]

Unclescratch

Just wanted to clarify. You are actually talking about the sheetmetal cracking not just the paint right? Just wanted to make sure I understand.

Could stop present crack by drilling end of it I imagine. You could stiffen frame. You could reinforce area where crack started( probably last resort. I am sure that somebody out there has solved this problem. Maybe there are some GTO racing clubs that have this worked out.

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1967 Firebird 400 conv T400 3.08, 1989 Formula 350 700r4 3.27