Why Some G bodies Rot Out in the Roof

[85 Cutlass Brougham]

I figured I would post this for all who didn't know. I have stripped many a G body for parts and noticed a disturbing trend. Some cars got the gray green rustproofing primer applied to all panels before welding, and some did not. So, the areas inside the box sections of those cars tend to corrode at a much faster rate than the primed ones, thus causing the dreaded roof rot we all have seen. I know this because my car is one of the unlucky ones, and I cut sections off the roof of an unrusted car. The one I cut from was back primed, while my car showed no evidence of this treatment, and rusted out after only 8 years and 61k miles. My latest solution to the problem was to cut out all the rusted metal back to clean metal, and stress test the rest of the roof with a pick to find areas that were soft, and replace them too. I then mudded them with either all metal or Bondoglass to seal the exterior from moisture from the back side. Normal Bondo on a weld seam acts like a sponge and will rot the car back out over time. I then back painted the roof as best I could with Rustoleum, and followed it up by shooting 3M's internal panel coating into all the seams to further slow the progress of future corrosion. I also replaced the seam sealer that always peels out of the drip rails with JB Quick epoxy. I had tried seam sealer before and it dried out and peeled back in 2 years and allowed water back in. The epoxy does not shrink, so it should last longer.

 

[crappycutlass]

the worst is the vinyl tops... my 84 you could see the rott under it.. we are too scared to take it off!..

my 87 cutlass was a mint car.. till we removed the vinyl...yikes..

i also haven't seen a perfect top car in a long time..

 

[82cutty]

I just picked up an 82 out of WV and western MD. I had severe frame rot and mild 1/4 panel rot in front of the wheel and minor after the wheel. Funny thing is the rear bumper was full of holes and about to fall off, but therest of the car was fabuolus. No rot in the floors, or trunk, some small rust spots in the trunk lid and rockers. The doors have the peeling rusy paint and thats it. The half top is rust free and no signs of dry rot. The frame rails were rotted so bad the wrecker towing it homew had to move to the front of the wheel area of the frame. Low and behold the car was most likely driven on a lot of dirt roads or gravel...... I had a 76 Cutlass and of all that I saw or bought always had one or the other 1/4 rotted. Gm never did a consistant job of rust proofing yrs ago until recently...

 

[pontiacman469]

Ive torn apart and put some back together 10-12 from 78-88 the worst is the laundu roof i had a 78,81 and 88 same issues..the other bad spot is the chrome trim on the bottom,pull it off and wow!not sham wow,but wow! :shock:

 

[STLRegal]

yeah, my regal has the dreaded roof rot, i blame on the shitty laundu top it had. The thing about roof rot that is bad is because its a very flat, but still curvy part where it is not easy to cut out and replace and make it look straight again. Doesnt help that it is on the most easly place to spot problems on a car. I sealed the one hold and pitted holes in with fiberglass so hopefully it will hold.

 

[Blake442]

I think the biggest part of it is the environment that the car is exposed to. 85 Cutlass Brougham, you're in florida, and though most would assume a rust free climate, the salty air gets trapped inside those unprotected areas, and bam, you've got rust. Same thing in California. That ocean air can be hell on cars. Granted, the inconsistancy of the coatings inside the cars also had a great deal to do with it as well...

That's why you'll see the theme of southern cars rotting from the top down, while the northern cars rot from the bottom up...

I had an '87 Cutlass Salon that was a North Dakota car, with a vinyl top. They don't use salt on the roads up there, and the frame was clean, but there was assorted scabs and rust around the car. I removed the vinyl top because I was going to paint the car at school, but I ended up parting it out after the engine blew. There was not a speck of rust anywhere under the top, around any edges, or around any of the typical seams. I was very suprised after all the horror stories I had heard. This was in '03 and the car had 145K on it...

 

[SV6 REGAL]

some had a sound deading foam in the a pillars and if water gets in the its toast

 

[85 Cutlass Brougham]

Well, the problem in Florida is not so much the salt air ( that is only near the coast) but the humidity. The air is always thick with moisture here.

 

[Blake442]

True dat

 

[pontiacgp]

my GP was originally from Florida and when I took the vinyl roof off there was no rust so I was lucky.....