Rust across firewall, how bad is it
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Joined: May 2007
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From: CPT (Southern Cali)
Car: 09 GSXR/88 iroc/91 RS B4C
Engine: 600cc/l5.7/5.7
Transmission: 6 speed/TH 350/auto
Axle/Gears: 45tooth rear?/3.23/3.42
Rust across firewall, how bad is it
while fixing some rust across my drivers floor pan i noticed some rust across my firewall right below the dash on the passenger side, i've always noticed a clunk between 1-2 shift but i always figured it was my shift kit, seeing this rust makes me realize my frame might be weak, im looking for opinions on how to fix this rust, or if its even fixable, just scrapping the car is not an option as i have too much money invested in other areas. need some input pls, by the way once i finish my floor pan rust i will add some alston subframes


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Joined: Mar 2006
Posts: 683
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From: Florida
Car: '87 Trans-Am
Engine: LB9 (305 TPI)
Transmission: 700R4
Axle/Gears: 3.42 or 3.73..figuring it out still
Re: Rust across firewall, how bad is it
That's not that bad...it can be cut out and fixed relatively easily. Can you get to the other side of that on the firewall? Either way, there is not that much there and it is along the seam...cut it out and weld in a piece there on the bend...reseal and paint it.
Thread Starter
Senior Member
iTrader: (1)
Joined: May 2007
Posts: 754
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From: CPT (Southern Cali)
Car: 09 GSXR/88 iroc/91 RS B4C
Engine: 600cc/l5.7/5.7
Transmission: 6 speed/TH 350/auto
Axle/Gears: 45tooth rear?/3.23/3.42
Re: Rust across firewall, how bad is it
i figured that thanks, what type of sheet metal should i use i have 16 gauge now would the be enough, and no i cant acces from the engine bay, not unless i take off my heater/ac box
another question is what type of insulation should i use i scapped the old carpet and under carpet tearing everything off, i will use por 15 on the floor once its all done but need to look into some type of heat and noise barrier
another question is what type of insulation should i use i scapped the old carpet and under carpet tearing everything off, i will use por 15 on the floor once its all done but need to look into some type of heat and noise barrier
Joined: Aug 2006
Posts: 12,805
Likes: 107
From: Central NJ
Car: 86 Trans Am
Engine: 408 stroker sbc
Transmission: TKO600
Axle/Gears: Moser full floater m9, 3:70 trutrac
Re: Rust across firewall, how bad is it
thats a commoin rust area.
its fixable, but its a lot of work to do it right. Just make sure you get all the rot out before you weld it back up, then seal it really well. Removing the a/c box will really help.
its fixable, but its a lot of work to do it right. Just make sure you get all the rot out before you weld it back up, then seal it really well. Removing the a/c box will really help.
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Joined: Mar 2009
Posts: 108
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From: Champion PA
Car: 84 monte carlo ss 85 camaro z28
Engine: 350/350vortec
Transmission: turbo 350/700r4
Axle/Gears: stock posi
Re: Rust across firewall, how bad is it
anythings fixable ive seen worse but it clunking from first to second is not good.i would get that piece of floor out of a junkyard car and weld a new seam in then put new subframe connectors in.
Joined: Jun 2000
Posts: 5,364
Likes: 51
From: Enschede, Netherlands
Car: 82 TA 87 IZ L98 88 IZ LB9 88 IZ L98
Engine: 5.7TBI 5,7TPI 5.0TPI, 5,7TPI
Transmission: T5, 700R4, T5, 700R4
Axle/Gears: 3.08, 3.27, 3.45, 3.27
Re: Rust across firewall, how bad is it
Why is it that these cars have rust issues everywhere there's sealer? Is there a possible issue with the sealer used and the e coat? A typical area is the rear tire storage area, The seams with the filler have the rust, nothing else. Luckily for me, mine have only a little surface rust there but my 87 has little rust issues under the seam filler on the rear panel, just above where the bumper mounts and some light surface rust under the a pillars. Very typical that the issues would start there.
Thread Starter
Senior Member
iTrader: (1)
Joined: May 2007
Posts: 754
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From: CPT (Southern Cali)
Car: 09 GSXR/88 iroc/91 RS B4C
Engine: 600cc/l5.7/5.7
Transmission: 6 speed/TH 350/auto
Axle/Gears: 45tooth rear?/3.23/3.42
Re: Rust across firewall, how bad is it
yes i do have rust along where the sealer is mainly, but i do plan on fixing it one thing at a time, and then eventually adding some sub frames.
this is what else im dealing with
drivers side

passenger side fixed

my drivers side floor
this is what else im dealing with
drivers side

passenger side fixed

my drivers side floor

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Joined: Jun 2000
Posts: 5,364
Likes: 51
From: Enschede, Netherlands
Car: 82 TA 87 IZ L98 88 IZ LB9 88 IZ L98
Engine: 5.7TBI 5,7TPI 5.0TPI, 5,7TPI
Transmission: T5, 700R4, T5, 700R4
Axle/Gears: 3.08, 3.27, 3.45, 3.27
Re: Rust across firewall, how bad is it
Yeah, weird huh especially since it seems the whole car is e coated/zinc dipped whatever. You'll quickly find out when welding, it's even visible in your pics, the yellow/white traces aroudn the welds are the edges of where the zinc burned off (which makes it a pita to weld in spots where you can't properly clean down to bare metal) The sealer GM used must have been acidic or something and compromised the zinc layer, or the sealant wasn't put on carefully and retains water.
Thread Starter
Senior Member
iTrader: (1)
Joined: May 2007
Posts: 754
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From: CPT (Southern Cali)
Car: 09 GSXR/88 iroc/91 RS B4C
Engine: 600cc/l5.7/5.7
Transmission: 6 speed/TH 350/auto
Axle/Gears: 45tooth rear?/3.23/3.42
Re: Rust across firewall, how bad is it
originally a Wisconsin chp car, moved out to southern cali in august 08. now a sunny southern cali car(well not today its raining one of the few days)
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Joined: Jun 2002
Posts: 270
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From: Taylors Falls, Minnesota
Car: 1983 Z/28
Engine: Edelbrock 355
Transmission: T-56
Axle/Gears: 3.42/Zexel/PBR
Re: Rust across firewall, how bad is it
I had a similar rust problem on my drivers side, however it wasn't quite as extensive. The repair turned out very nicely. I have a rust free titleless parts car I didn't feel bad cutting up to save my Z
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