modding 77 gas filler to newer 81-87 style

[gramps77]

So I just cut out left and right refuel areas from an 86 3-4 inches all the way around. Dont worry, that bed had been rearended so I didnt cut up a perfectly good bed.
Can someone give me the measurments for where the top corners of the doors should start from the top of the bed?
It'll be nice to not get gas everywhere when I refuel here in Cali with those stupid nozzles. Then, on to a repaint.

[ray_mcavoy]

I don't have any measurements for you, but I can tell you that you might run into an interference issue with the clearance humps on the inside of the body if you put them in the stock locations.

I did just the opposite on dad's 77. Back when we did the restoration, new GM bedsides with the round holes had been discontinued but the ones with the square holes were still available from the local GM dealer. So I cut the square area out of a new bedside and welded in a panel with the round hole cut from a donor truck.




When test fitting this new bedside, I noticed that the filler neck clearance hump in the 77 bed floor didn't completely cover the corresponding notch on the inner bedside panel. Evidently GM made the bed floor filler neck humps wider on the trucks with the square filler doors for extra clearance. When going from square to round like I did, it was a simple matter of welding in a small filler piece to the inner bedside to reduce the size of the notch. But going from round to square might present a clearance issue ... I'd definitely recommend mocking things up with the new filler neck before you make any cuts.

In hindsight, I should have cut rounded corners on the patch panel. The squared off corners were harder to butt weld. And even though I had a tight fit between the pieces, made small spot welds, and allowed plenty of time for them to cool, there was some panel distortion that occurred as the weld spots cooled & shrank. It took a bit of hammer & dolly work to planish the welds and bring the panel back into shape.

[gramps77]

well thats not good news. I suppose I may have to mount it a bit lower. Although, Ive read your info about 5 times and Im still confused where it didnt clear cause the truck I pulled them out of had the same size humps in the bed as my truck

[ray_mcavoy]

Originally Posted by gramps77

Although, Ive read your info about 5 times and Im still confused where it didnt clear cause the truck I pulled them out of had the same size humps in the bed as my truck

Unfortunately, I didn't take any pics of that area during the work. But here's a pic of the area in question.



The new GM bedside with the square filler hole actually had too much clearance to mate up with the hump in the bed floor and would have left a gap. The dotted line I drew on the pic represents the size of the notch before I welded in a piece to make it match the hump.

Years ago, Dad had replaced the passenger side bedside with a new GM one that had the round hole and that one matched up perfectly with the hump in the bed floor. The driver side bedside is the one I modified from square to round hole to match. So when I came across this difference in the hump/notch, I assumed it had to do with the square vs. round filler hole. But maybe there is some other factor involved. Since the humps in your truck's bed floor are the same size as the ones in the donor truck this might not be an issue for you after all.

[boilermakerny]

I am trying to do the same thing with my truck - I don't suppose you guys know of a place that sells just the filler hole? Or do I need to find a donor bed?

Thanks!