F41 and aftermarket bracing diagrams (MORE pics added)

[Clone TIE Pilot]

Ive always found it interesting, so many people spend time making these aftermarket X braces and putting them in places (behind back seat, radiator support, monte carlo area) and find it as not being much more than somebody who is reinforcing areas that are not overly prone to flexing with respect to noticeable need to do so. Im only stating this as an observation that quite a few people have done. Ive not heard much as to its overall positive affects in changing much, unless its clearly obvious that your engine size and related torque produced is significantly bigger than even mildly built engines, so as to make the argument that the BIG HP, TORQUE motors are flexing areas on the car enough to warrant a need for bracing. Am I just seeing this all wrong, or is it that some people just like to do it for the sake of doing it? Just my observation, and no other reason for my post.

The rear seat braces along with the number 5 body bushings cut down on the rear pillar flex which causes roof/quarter seam cracks on the exterior. Every G body should have came with them and all probably need them, even those with base V6s. My 231 V6 still had enough power to flex the rear pillars enough to crack the roof seams. For the rear seat brace to work its best, you need to have the number 5 body bushing installed (many base models don't have the #5), and the rear seat brace should be welded in to prevent any movement and oblonging that fasteners would have.

 

[Brother Al]

Yes Indeed!

When these cars were initially designed, each GM Division stil had their own design teams, so each G Body model has their own unique quirks and solutions to problems in the chassis' weak points... Pontiac did the most with it, but it didn't matter once GM started the next level of Corporatizing and "Faux Luxury" re-classifications.

Additionally to the above... the reinforced rear trunk braces found in all Grand Prix's. Essentially it is a modification of the jack holder on the pass side, found on all G-Body's, with a secondary supporting brace tied into it, plus a mirror-image version used on the driver's side. These are spot welded to the top of the Quarter panels where the rain/water channel of the trunk seal is and on the bottoms they are spot welded to the Trunk "Drop-off" panel on both sides. The purpose is twofold. It was Pontiac's solution to take some stress off the rear framerails and keep the quarters and rear panel rigid... thus helping prevent the whole trunk area from "squish-flex"... ie. the trunk lid pushing downward and the quarters flexing outward... This leads to additional stress on all of the panels weld points and places additional downward stresses on the rear framerails, causing cracks... I rarely find GPs with cracked framerails, just rot.
Again because of the way these were built/designed, the rear section is "floppy" (as discussed all over this site and elsewhere numerous times).

 

[pontiacgp]

If the frame doesn't twist the body won't either and I have never seen the filler over the quarter panel and roof joint crack. Even on my t-top when the body bushings were so shot the back of the car slide side to side depending on which way I was turning there was no cracking of the filler covering the joint...

 

[Clone TIE Pilot]

Well mine did even with just 110 HP twisting the body. Through my car lacked number 5 bushings and yours probably had them.

 

[Brother Al]

Again, see my above post Pontiacgp... As you know, Im a Poncho guy too... I have seen a lot of Cutlass' and Regals with cracked/broken filler in the quarter to roof seams and Montes, Cutlass', & Regals with cracked frame rails just past the rear part of the frame's axle arches... this is the weakest area in the frame for up/down weight transfer causing flex/stresses... not so much with the Grand Prix, again, its those rear trunk floor braces... pre '78 cars utilized actual floor bracing for the trunk that tied into the rear boxed area... '78-88 cars lack both. GM shaved a lot of structure/weight/cost out of the traditional A Body "ladder" frame by deleting all kinds of bracing and structure.

Over time and use, that flex causes the rear of these cars to flex like a hinge in the back-half during normal driving.. that's also why the sealed seams in the trunk area fail and lead to rot along them... add in Rustbelt roadways with salt and deep potholes... you end up with many unusable G Body cores up here.

 

[pontiacgp]

I guess with a neglected car over 20 years old rot can be expected

 

[GT_80]

I guess with a neglected car over 20 years old rot can be expected

sometimes even a well cared for car thats ten years old can have rot- my 2003 Sierra I bought when it was 7 years old, and after 2 winters of me driving it, even garaging it in really bad weather and washing it every couple weeks during the winter, the rockers started to rot out.

 

[Donutboy97]

does anyone have a good close up picture of how these bars mount to the firewall? I can't figure it out-

probably not the best pic... On the Monte's, I'm guessing the same can be said for all G-bodys, there are two dimples on the cowl. that's where you drill the hole for the bolt. the bolt goes up thru the bar and cowl and the nut is on top.

 

[Clone TIE Pilot]

I installed a Tinman's rear seat brace by plug welding it in with my MIG.

Here is a GN thread that has some info about rear seat bracing.

http://www.turbobuick.com/forums/threads/rear-seat-brace-pic.410191/

 

[Clone TIE Pilot]

Here is an article talking about how stiff old Austins bodies are, and they used a pretty familier looking brace in the rear. http://www.autospeed.com/cms/article.html?&A=113020