Cab top bulge? Any one seen this before?

[100gold]

Here's one for you guys. These are pics of both , my parts truck and my project. Some of the pics are tough to see but the gist of the problem is that on both trucks, there is bulge where the top of the cab meets the drip rail on the passenger side directly above where the a pillar meets the drip rail.

Our theory is that water builds up and freezes, creating the bulge. Anybody else seen this? And what do you think?

[2tons of fun]

what does freezing have to do with it?

that what happens when heavy rust is forming, the water is penatrating into the steel itself, is cause it to swell and grow and flake.

[69GMCor70Chevy]

I live in Canada and I haven't even seen one that bad. Unless it was in an accident.

[100gold]

We've had this truck since 85 or so. When we bought it with 45,000 miles on it the bulge was there.

It was always thought that the truck had taken a hit on that corner and caused this.

When we tore it down to restore it this past couple of weeks I was astonished to see no evidence anywhere that the truck had been in an accident.

Our theory is that water has frozen in that corner somehow. Again, no evidence of ever having been in an accident before the one that parked it in the late 90's.

[100gold]

Also, note that both trucks have the same bulge.

[Shane]

looks like warpage due to an experienced person using a sandblaster

[ebfabman]

^^^yup^^^

[*Dylan]

Don't see how it could be water freezing. When water freezes it contracts. Heat makes stuff expand. Warpage from a sandblaster building heat like Shane said could be good cause for that.

[dano327]

Your theory could be rite, It is the same effect as a engine block cracking when there is no antifreeze and the water freezes causing a frost plug to pop out or worse the block to crack, that area is prone to leak the sealant drys out and water leaks in usually rusting out top of window frame, It is amazing how much damage ice can cause

[100gold]

Dano327,
Tell me more about that area being prone to water leaking in there. We're going to have to cut into it and put a patch of some kind in it to get the right curve back. I'd hate to not fix a known problem while we're that far into it.

I guess we'll figure it out when it comes apart to see what we need to reseal.

Dylan,
Where'd you go to school? That's funny.

Ebfabman and shane,

Parts truck has original paint with same problem. This truck has never been touched before now. Bulge existed before any sandblasting occured. I apologise for not writing so that you could understand what I was trying to say.

[*Dylan]

I stand corrected, water is one of the few things that expand as they are frozen. Insulting my intelligence wasn't the best way to go about getting your point across though.