long bed bed to frame bolt pattern
 

The bed to frame bolts at the front of a long bed bed have three recesses in the bed floor for bolts and two different patterns. Some use the front two positions and some use the first and third position with longer bed to frame bolts in that third position. I'm trying to figure out if there is a specific year break, chassis style, etc. that this pattern follows.

If you have a long bed truck I'm asking if you can look at the two sets of bed to frame bolts and post the following: 2WD or 4WD, year, and which two holes are used (1 and 2 or 1 and 3)

Thanks!
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Re: long bed bed to frame bolt pattern
 

From what I've seen, it has to do with the chassis style (specifically the forward leaf spring hanger brackets). Although there might be some year range differences too.

I believe it's only 1/2 ton 2WD trucks that use what you described as locations #1 & #3 with the longer bolts at #3.

All 4WD as well as 3/4 & 1 ton 2WD have extra reinforcement brackets that connect the forward spring hanger brackets to the underside of the frame. These brackets would interfere with the longer bolts used in the #3 position. So these trucks use #1 & #2 locations and have all 8 bed mounting bolts the same length.

Re: long bed bed to frame bolt pattern
 

Two that we've checked locally: '85 4WD, dual 16gal tanks, built in Oshawa uses 1-3. '82 2wd, single 20 gallon tank, using 1-2.

Also checked '83 1/2 ton 2wd built in St Louis using 1-3, another '82 2wd using 1-2 and an '86 2wd 1-3.

Re: long bed bed to frame bolt pattern
 

we sent a pair of 76 4x4 trucks to Pennsylvania- one long and one short. the long was missing the bed but i had a long bed from a 73 2wd i was going to turn into a trailer so we put it on the 76 long truck and a couple of bolt holes wouldn't line up. the gentleman still has it since he built the short 4x4, we filled it full of parts for him prior to shipping.

Re: long bed bed to frame bolt pattern
 

every one I've ever had the bed bolts go thru the frame at the front leaf spring mount. 1/2, 3/4, or 1 ton. but they were all 81 and newer.

Re: long bed bed to frame bolt pattern
 

Evidently, there is a bit more year-to-year variation than I thought. I just checked a few examples in Dad's junkyard and some reference photos I had saved of well-kept originals from various online ads and found the following:

1973 GMC C15 parts truck with no bed, but holes in frame at #1 & #3 (no holes @ #2)

1977 GMC K15 (pics from Rust Free Classics) using holes #1 & #2
1977 Chevy K10 (pics from ClassicCars.com) using holes #1 & #2

Dad's 1977 GMC K15 with E81 wood floor using #1 & #2
1977 GMC K15 w/steel floor using #1 & #2
*I took a close look at the spring hanger reinforcements on these and found that they would not interfere with bed mounting bolts at the #3 location as I had previously assumed. In fact, the reinforcements have holes punched in them where bed mounting bolts could pass through. However, the frames on both of the 2 above listed K15 trucks do not have corresponding holes in their frames at location #3.

1977 GMC C15 (pics from an old Barrett Jackson listing) using #1 & #2
1979 Chevy C10 using #1 & #2
*These two examples contradict what I posted earlier, being that they are both 1/2 ton 2WD, but using #2 instead of #3

1984 Chevy C10 using #1 & #3
1987 Chevy C10 using #1 & #3

I also have an 8' bed with a steel floor that came off an unknown truck (I acquired it as a homemade trailer on something other than a GM frame). I believe it's off a 78 because it has the newer style tailgate hardware, a round gas filler hole, and black accent side trim. I don't know what it came off in terms of GVW or 2 vs 4WD, but it has mounting holes at the #1 & #2 locations.

Based on this info, it looks like GM may have switched back & forth over the years, with there being a time in the mid 70's to early 80's where they all used #1 & #2.