Ok, here we go. Got the pics and the MAIN difference is the ends outside the main strip. I didn't use a tape measure because the comparison is between the two.
Generally speaking, both strips are CLOSE. But not close enough on the ends. The ends are vulcanized to the main strips with the plastic push pins. The ONLY real difference I can find is that the last 2 pins on either end of the 81-88 version are smaller diameter than the 78-80 for some reason. Not a huge deal, but it is a factor of difference. That alone would explain instantly why another part number was issued. Both sets come with the plastic inserts infused in the end "plates" for the mounting pins. Speaking of mounting push pins, you need 8 of GM p/n 8731909 or aftermarket equivalent to put these on your car, whichever version you use.
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But it doesn't stop there. The 81-88 is APPROXIMATELY 1/2" longer than the 78-80 counterpart. Why? I don't know. Again, that's just a guesstimate. A plus or minus, uncalibrated eyeball measurement.
The ends are where the real differences are. The mounting pin locations are the same on both sets, but because of the 1/2" or so difference in length overall, and it's in the front. You'd have to push the 81-88 version together some on the front (A-pillar end) to make it clip onto the 78-80 door factory holes. Conversely, you'd have to stretch the 78-80 A-pillar end about 1/2" to align it to the right spot if you put it on an 81-88 door.
The front (A-pillar end) is slightly different in shape and thickness in some places. How it arranges itself into the door and window area seat appears that there would likely be permanent wind noise at best, and gaping water intrusion at worst.
The rear (B-pillar end) piece has even more obvious differences. I'll let the pics show you. It's really unfortunate because the side window strips where they meet are the same for all of them. They DID change part numbers on the side sealing strips later on but the reason was a redesigned part for better window sealing/wind noise control over the original part numbers. Had nothing to do with the fit and shape where it mounts and seals against the door weatherstrip.
84 W40 can back me up on that.
Additionally, it is recommended that a VERY THIN bead of
black 3M weatherstrip adhesive on the mounting pin surface area on the bottom. Don't need much thickness. Just remember to go around the outside of the pins with it. I say black because that yellow stuff looks like azz if you squish any out. It does not have to go all the way up to the ends. IIRC, the 84
H/O only had the adhesive going up about 1/3 of the sides of the door. There obviously is a reason for this. I imagine this was done for water spray intrusion from the bottom area of the door seals where the body break line curves under, allowing front wheel splash to blast into the door gaps. But I'm not sure exactly why. My memory is a bit vague on this and I'm not sure what I did with my Fisher Body books. It may have something in there for that. But, whatever.
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20008189 VS. 20201221
In this corner, the OG, weighing in at around 1 lb, the ubiquitous, the world-famous 78-80 (and some 81s) LH DOOR WEATHERSTRIP!
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And the challenger, weighing in at approximately the same 1 lb, the younger, and slightly longer up and comer, the 81-88 Cutlass/Regal LH DOOR WEATHERSTRIP!
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In the pic below, you can see how the ends are SORTA shaped the same, but there's a wider transition channel in the center where it meets up with the upper side window seal section, as well as a more defined Stone Henge looking brick "hump" where it meets up with the inner door panel and it's slightly wider overall. The 78-80, which is pictured on the right, is smaller and more rounded. It's just...different. Mounting pin locations seem to be in the same general location.
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78-80 on the right.
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More slight differences on the door side that you don't see when mounted on the door. Again, 78-80 on the right.
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Another close-up of the back side of the B-pillar end. Note how "tall" the 81-88 end is in comparison to the 78-80 version.
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Pick and end. Either end. 78-80 on the right. The two end pins on either end are smaller diameter than the 78-80 version. Why? I have no idea.
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Below you can see the 81-88 version SLIGHTLY longer on the A-pillar end. Not by much, but it's still longer. 78-80 version on the right.
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This is the money shot, per se. The A-pillar end shapes where they meet the door are very different between the 78-80 version on top, and the 81-88 version on the bottom.
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End view of the A-pillar end. You can see there's quite a bit of difference in the nooks and crannies. 78-80 version on top.
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This time, the 78-80 version is on the left. But you can see where the top mounting pin area is flat where on the 81-88 version it has a tweak in it and it isnt' flat against the door. Keep in mind, to put these even with each other, the alignment pins had to shift down slightly but you can't see it in this picture.
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God forbid if you tried putting these on a Monte Carlo or GP. If I had a sent of those, I'd compare them too, but I don't. So this is as good as it's going to get.
The myth is busted. But not by much. At least between these two versions. But, it's A/G door weatherstrips are NOT interchangeable everywhere. You have to make sure you know what these fit. Good thing is that the 78-80 version fits ALL A/G El Camino/Caballero doors 78-87. That's only one part number set you have to remember for those. But that's it. If the number is different, so is the part.
Now, if you have good "ends" but a chunk missing in your A/G door weatherstrip between the ends, I'm willing to bet you could cut out the needed chunk from any good A/G body set and be able to fix them, keeping in mind that some may have smaller pins near the ends. The repair probably wouldn't be concours or show quality, but with some black 3M weatherstrip adhesive, and a good steady hand, you may can at least repair your chunked ones at least to function and STILL have that GM softness and sealing capability that GM was famous (or infamous)
I'll add one thing since you did't include the disclaimer like all the places selling parts for these cars, "Don't fit Cutlass Supreme".
Just had to. Now back to the real usable info & don't pay any attention the the Chevy guy.
you are right about that, i found that when oder a set for my 87 cutlass superm disclaimer said it fit all gbody that year. i had to make them work but i am not satified with fit. parts for cutlass are not the same as monte carlos,buick or malibu's no matter what the the disclaimer say's
Calm down. You're good.
