Id'ing original sheet metal?

[Danmcg]

Is there a way to tell if a fender is original or aftermarket? Are there any stampings on the original sheetmetal that I can look for?
I've got a few doors and fenders kicking around and some sound tinny when you tap on them making me think they're after market, but there has to be some stampings or part numbers on them to know for sure.

[Dads79GMC]

I saw a pair of NOS fenders years ago, may have been older ones, that had GM stamped on the inside of the wheel opening. I'm not the expert! I'll check the one I have now. Mike

[Danmcg]

Thanks Mike.

[79Silv4x4]

Just a thought of mine on this topic.. Does aftermarket sheet metal not fit the same as OEM or is the difference just the thickness/quality of the piece? If it's just the thickness/quality then why not make it to OEM spec and charge accordingly? If they already have the tooling necessary then why not produce as close to an OEM product as possible? After all, I would think that anyone buying these parts now is more interested in quality than simple crash repair.
Just curious...

[gmachinz]

On the 81-up fenders at least there is a machined "pinch" on the front and rear of the wheel well lip-it is there to correctly locate the inner fender skin to the outer prior to automatic pinch welding the two pieces together-I've not seen this manufactured "alignment pinch" on aftermarket fenders-perhaps 73-80 also had them?

[Jrgunn5150]

Look inside for black ecoat. Most people aren't going to paint them way deep inside.

[75C10]

Not wishing to set off a fire storm here but how does the presence of e-coat relate to OEM or repro parts?

My GM supplied fender, doors, hoods etc that I purchased in 1991-1992 were e-coated. Still have the parts on my truck. And repro parts are also e-coated.

I am unaware if there are parts repo'd that are bare metal.

[Mattchu60]

I am wondering about this same thing - I was looking at a pair of NOS GM fenders the seller claimed. I asked if there are any markings to show they are GM, said they didn't get stamped with any markings but you can tell by the feel and also they have the nuts for the radiator support bolts welded to the backside. I have never seen a aftermarket fender, but I assume this means the aftermarket ones don't have the nuts welded to them? Maybe I was being taken for a ride, not sure.

[Jrgunn5150]

Originally Posted by 75C10

Not wishing to set off a fire storm here but how does the presence of e-coat relate to OEM or repro parts?

My GM supplied fender, doors, hoods etc that I purchased in 1991-1992 were e-coated. Still have the parts on my truck. And repro parts are also e-coated.

I am unaware if there are parts repo'd that are bare metal.

I guess it's splitting hairs, but if it's e-coated, it's a replacement, and not OE. Where the replacement comes from is another matter, but it's not the original fender/door/whatever it left the line with.

[75C10]

If there is anybody that will know if GM produced sheet metal can be identified without its part number affixed or outside of the unopened cardboard shipping box it is Mr. Seymour. Of course using NDT (ultrasonic testing) will also easily and quickly ID the allegedly thinner repro metal.

Keith you can weigh in anytime please.

[gmachinz]

The GM NOS 77-up doors and 81-up hood, fenders I had a couple years back were e-coated and were in GM boxes still along with the blue/white GM sticker too. "older" years stuff pre-1980? NOS sheetmetal were epoxy primed. I just picked up a pair of NOS (and still in the boxes sealed) fenders for my father in laws 1977 GMC recently and they were e-coated as well.

[Jrgunn5150]

Originally Posted by gmachinz

The GM NOS 77-up doors and 81-up hood, fenders I had a couple years back were e-coated and were in GM boxes still along with the blue/white GM sticker too. "older" years stuff pre-1980? NOS sheetmetal were epoxy primed. I just picked up a pair of NOS (and still in the boxes sealed) fenders for my father in laws 1977 GMC recently and they were e-coated as well.

My question then would be, who is supplying GM with them? Are they over runs from the line? Or are they from outside suppliers under license?

I'm an engineer in a stamping plant, we are a tier 1, 2, and sometimes 3 supplier, depending. So some panels we bang out, go straight to an OE and on a car, others are for service, others go to another company and have additional things done, etc etc.

[gmachinz]

idk the answer to that....most of my NOS sheetmetal was purchased from a GM dealership who sold off their vintage stock for 10% above their cost back in about 1988/89.

[1774btcrew]

Can you show a pic of the machined lip on the fenders you are talking about? I have found a seller that supposably has 2 NOS 81 up fenders and 2 doors. They aren't in their original boxes and have already been jambed. These aren't a bargain so I would like some reassurance.

[1774btcrew]

Originally Posted by gmachinz

idk the answer to that....most of my NOS sheetmetal was purchased from a GM dealership who sold off their vintage stock for 10% above their cost back in about 1988/89.

Any answers Jabin?

[gmachinz]

Sorry-Ive got a lot on my plate right now....I snapped a few pics of a RH GM fender I bead-blasted and my NOS fenders also have these alignment "dimples" I call them. Aftermarket fenders dont have these-there should be 4 total-these were used to align the inner/outer fender shells together and hold in place prior to being pinch welded. Here are the pics of a factory fender lip for 81-up:

[gmachinz]

Here are a couple pics of an aftermarket LH front fender on an 81-up parts truck I have-notice the lack of alignment pinches in the general area where they are in the above GM fender pics. These pics are of the front and back of the front LH fender lip-the lack of the proper alignment pinches near the wheel trim holes indicate this truck has aftermarket front fenders. This is what I look for when shopping for used or junkyard fenders.