I know this topic came up a few years ago, and someone was going around at shows and trying to count the cars that had this problem. With some of our cars nearing 25 years old, I can see this becoming a much larger issue. My 85GT has close to 275,000 miles on it. I drive the living hell out of the car, especially with the V8 and 5spd in it now.

This crack was only a hairline about a year ago and has steadily gotten worse. I can only assume that it has something to do with the way the cradle is loading the body/chassie of the car.

Does anyone else have this crack this bad, has anyone seen it go beyond this, should I be really worried. I have been considering retiring the chassie of the car and buying another 85GT and moving all my drive train/suspension/body/interior over to it.

So who else has a nasty crack showing in there backside. (joke intended)

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85GT 5spd ,93 Eldorado 4.9 Dual O2 Custom Chip, Archie Clutch. Custom Exhaust. MSD Everything 245/50/16's Not Your Average 4.9 Capt Fiero Com --- My Over View Cadero Pics Yellow 88GT 5spd Stock.

Wow, that's interesting. I've got a rattle in mine that i can't find. The sound is coming from that area. I think I better go look. 214 thousand miles. Might be a few broken welds. JM

I would grind the area clean and mig weld the seam as soon as possible. I have not seen this on any of my Fieros and some are high miles cars. I would be concerned with a split such as you've shown and would immedialtely address the problem.

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87GT 3.4 Turbo- 0-60 5.2 seconds -Best
Engine Controls, ECM goodies, Chip
re-programming & odd electronics stuff

If it were me I would take it to a reputable body shop in town, and have them put the car on the frame rack; then have them pull it back together and then just weld that crack up. Problem solved and will probably last another 200,000 miles. And where it is at probably won't cost an arm and a leg to fix.

It would be interesting to see if the metal is deforming or if welds are breaking or tearing out.
The crack that you see appears to just be in the putty that's used to seal the seam.

Maybe a brace needs to be manufactured to span the gap between the shock tower and the trunk beam. Similar to how the dogbone bracket braces the other side. (Rodney? Worth investigating?)
Someone who was dismembering a chassis with a sawzall, and in a position to experiment, posted that the right side was much stiffer due to that bracket.

I wonder if the amount of rust on/in the structure plays into this.
IOW, I wonder if rust-free, southern or desert cars would fare any better or if it even makes a difference. (I suspect not, since Tina posted about having the same problem. I'm pretty sure that her car was gone over with a fine tooth comb before the project was even started. I suspect that a rusty chassis wouldn't have been used. NOT to imply that your car is rusty, David.)

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Raydar
88 4.9 Formula IMSA Fasback..........................88 3.4 coupe................................................

Read Nealz Nuze! Praise the Lowered!

[This message has been edited by Raydar (edited 03-06-2007).]

That may just be a crack in the seam sealer? dig in a bit...maybe?

Well I just went out and checked, Lisa's Fiero's. Her SBC V8 powered with 90,000 miles is clean no cracks and I know it has been ran hard by the previous owner. Her 85SE V6 Auto 150,000 miles is crack free, and our friends 85SE Nitrous V6 4spd is crack free as well. However one thing I did notice is a huge variance in how the seam sealer was applied. The 88 is very thin, the 85's look they were puttyed on with a fork and the 86 looks like it was put on with smooth surface tool, very neat and clean.

Don't know if any of that proves anything, but all the cars here are pretty much rust free cars. The orangey yellow you see around my strut town in the pic is just wet clay type dirt from my bosses warehouse. All of my cars get liberal use of TremClad anti rust paint any time the suspension or engine is dropped.

I looked at both my 88's, they looked like the putty guy was having a rough day--spreading the stuff on with a garden trowel. But no cracks in the putty after almost 20 years. I don't think the cracks on your chassis are a good thing.

I think if I saw such a thing on one of my cars, I'd be concerned. Take it to a good frame shop and have it safety inspected. Probably (at least in the US) they won't charge you to have a look. Easier to avoid liability if they don't charge for an inspection.

Mine has a crack on the left side, but it is solid on the right side. But this is my SE that was hit from behind.

I don't think there is any metal between those points, just sealer. Over time the sealer cracks from the stresses.

But the large gap between the two sections of filler means that something is no longer in the position it used to be in. That's reason for concern.

I agree to a point. That panel is flexed from the dogbone pushing on it (the strut towers are probably moving too). Is someone seeing a change in the position? The ones I've seen are just cracked and the sealant fell out but the position was still the same.

Looks like our built-in strut tower brace doesn't exist though. Different topic for a different time.

It is just the putty. But, it would be kinda nice if there was a structural bracket like the dogbone bracket holding the trunk to the tower. My 84 has it pretty bad too.

That's a good point about the dogbone pushing on it. The trunk wall wasn't built to take a 4.9 heaving against it.

Well my car has never been hit from behind. Taken 2 good whacks from the front though, 30mph into the side of one Honda and one Chevy Citation. (people making lefts in front of me)

Now as to the dogbone theory. Hmm it never occurred to me, but, yup, hmm. The crack just happens to be on the drivers side. If the trunk wall was distorting due to the dogbone that would cause that seam to begin to crack. When we did my 4.9 I was having too much engine movement. So a friend of mine who happens to be a genius at building things, took an old V6 engine side dogbone mount, re-created it, and mounted it to the drivers side of the engine (head) then fabbed up a bracket to the drivers side of the trunk wall. With a bit of spare parts from a 4-link rear suspension we made a solid dogbone that would never break.

I will let the pics illustrate.

I wonder if this could be the entire cause of the crack.

I'd say there's a very good chance you've found your problem. The passenger side is stronger to take the force from the dogbone. The driver's side simply wasn't built for that sort of thing.

Like Jax184 said. But, I would think that part of your problem is that that dog bone looks like a a solid mount, there is absolutely no way any stress can be released or contained without putting tremendous force on the trunk wall. Do you have solid mounts on your engine? You may want to put a different style dog bone in there that has some sort of bushing so that it can move a little.

Just my $.02

quote Originally posted by Capt Fiero: I know this topic came up a few years ago, and someone was going around at shows and trying to count the cars that had this problem.

You probably read this thread https://www.fiero.nl/forum/Forum2/HTML/077992.html

I have actually been doing a little more investigation since then. At work I have been lucky to be involved in some life analysis on welded sheet metal structures and have been becoming friends with our analysis group. Unfortunately I don't have the time to model up an entire Fiero frame nor the ability to obtain dynamic loading events needed to perform a life analysis. What I have been able to do though is create some simplified models and perform some stress analysis. As I predicted the area in which your crack is forming is the area of the highest stress in my simplified model. The simple way to even out the stress is to replicate the piece which welds between the trunk wall and strut tower on the passenger side over to the drivers side.

With adding that dog bone mount where you did the stress in that area probably shot through the roof. Another thing I noticed in the parts car that I did my tests on was that there was a significant amount of rust forming between the strut tower and plate that formed the trunk wall. In my case I couldn't find any evidence that the rust had yet to affect the strength in that area but left alone it would undoubtedly be a problem. With the gap you have and where you live I wouldn't be surprised if you have significantly more rust. I would remove all the seam sealer, clean and treat the rust, pull it back together somehow and weld in the part I described above. Also the main thing which holds the strut tower to the trunk wall in that area is spot welds not seam sealer. Drilling out the spot welds and welding it back together wouldn't be a bad idea as the sheet metal is probably deformed significantly where the spot welds are.

Sorry that this is all from memory without any pictures to back it up. Unfortunately I never think to get the camera out at the right times.

holy god! thats crazy. get that welded up...

Yes Jefrysuko it was your post that I was remembering. Thanks for all the info. I will get it cleaned up with an angle grinder, then welded shut, and add some sort of re-enforcement bar between the strut towers.

Although I do live in Canada I am on the West Coast where the weather is much more mild than even the Mid West states. Rust thankfully is not a big issue here. I also make a habit of taking my car down and getting an under body wash done about once a month during the summer and twice a month during the winter just to keep road grime from accumulating on the undercarriage.

I think that may be shrinkage in the seam sealer. I got a 84 thats all stock, been sitting since 1990 with only 53,000 miles on it, never been in a accident and it did the same thing sometime between 3 years ago and last year even though it never moved from the back corner of the yard. One of my others has a trunk seam doing the same thing where the 2 panels lap each other I had a 1/8 inch gap so I stripped it back thinking I had a couple of popped spot welds or a stretched and split panel and nothing just shrunk sealer. By the way wire wheels in a high speed cut off tool works great on stripping out the old sealer but watch the launched wires most cut off tools exceed the wire wheels speed limit when not slowed down.

quote Originally posted by Capt Fiero: Although I do live in Canada I am on the West Coast where the weather is much more mild than even the Mid West states. Rust thankfully is not a big issue here. I also make a habit of taking my car down and getting an under body wash done about once a month during the summer and twice a month during the winter just to keep road grime from accumulating on the undercarriage.

Sorry I didn't realize you lived that far west. Here the roads have been white from salt for the past two months. They have also started spraying "liquid salt" on all of the bridges anytime there is a hint of moisture in the air. With all that salt it isn't uncommon to find a 10 year old car completely rotted away.

Good luck fixing it. Let us know how it comes out.

Capt, you may also want to consider moving your dog bone to a different location as well. It might be easier than going through all the extra work of beefing up that area.

I have mine running from the head (motor front) down to the cradle using a trailing arm from a Grand Prix (I believe) and so far have had no real issues. Another fellow in our area used a trailing arm from an import (he has no ideal which car he took it off - did not pay an attention) that was fairly close to a perfect fit (the Grand Prix had to be made much shorter).

You can see mine in this picture between the strut and the O2 sensor:

Some are the result of frame straightening after rear end damage. Check the measurment/ straightening holes on the frame rails underneath, they'll be deformed some if they have been used to realign the body.