The Stovebolt Site Forums The Shop Area Engine Shop Did 60-66 3/4's come with 12-bolt?

OK, so now that I've identified my burly H-072 rear in my '65 3/4 and found a 3.90 gear for the paltry sum of $468, I gots to know: Does anybody out there have a 60-66 3/4 with an original 12 bolt? Did they come with these? Maybe I'm just an unlucky one that bought a C20 with this odd, fat, round Eaton? Looking at the LMC catalog, all they show is a 10 bolt for the 1/2 tons and 12 bolt for the 3/4. What I'm gettin' at is I don't wanna fabricate. My truck is my daily driver so the less involved in the swap the better. Finding something original that gears cost only $200 seems ideal situation.

Mugsy,
As you have now noticed, 3/4 and 1-ton trucks are geared lower than 1/2-tons, for moving heavier loads. What I am going to do with my 1-ton '54 GMC is install the '67-'72 carrier with the 4.10 gears, then install a transmission with overdrive to improve the top speed. With the engine I'm working on, it will never break 100, but should be happy on the highway.

Do you currently have the 12 bolt, or is it a 10 bolt. If it's a 10 bolt you can swap the center section for a 4.10 gear like GMCPanel described. I think you can do the same if you have a 12 bolt. Another option is to get a 14 bolt corporate from a late model, and swap the spring and shock mounts. With the 14 bolt 3.73 gears are were standard, 3.42 are available in the newer ones.

I bought a '66 corporate rearend from a guy with a '66. (I don't remember if it's 12 or 14 bolt)
He had 3.07 gears put in it and then decided to swap in a '72 rearend to make up for the wider disk brakes he swapped into the front.

Sorry, it's not for sale, but it can be done. It's going into my '50 later on this summer.

Not for nothing, doesn't common GM language call a 12 bolt a half ton intergal rear with either 5 or 6 lugs depending on the year?And isn't a 10 bolt a similar unit? 14 bolt rears look similar but larger,they are all 3/4 or one tons,and somewhat wider than the 10 or 12 bolt.

Fred T., I got a 10 bolt but, it's a huge 10 bolt that I guess was used on some if not the majority of 3/4 tons. It's an H-072 (so I found out thru the help of this here forum) that nobody's got any kind of selection of gears for. So, I'm trying to see if anybody out there has a 3/4 ton, be it a C-20 or 2500 with an original 12 bolt. Like, could you have driven off the lot in 1965 with an 8 lug 12 bolt? If you didn't know much (like me) and you were looking at the LMC catalog for 60-66 you'd think 3/4 tons ONLY came with a 12 bolt. To make a long story short, I wanna know if these 3/4 ton 12 bolt trucks exist or if they only came with the crazy, fat 10 bolt that I've got. If these trucks exist(ed) than I can swap out with no fabrication, get cheaper and higher gears and be back on the road quickly. Anyone, anyone, Bueller.

Yeah, don't confuse this axle with the true "10 bolt". BIG difference. mugsy--as far as i know, this was the only axle used in 3/4 ton and 1 ton trucks, at least 60-66, and, according to my 60 shop manual, this axle was "used on all 3/4 and 1 ton trucks". As far a later years, I can't say that i've ever heard of a stock 12 bolt in a 3/4 ton. I just don't think they're strong enough to hold up to what some people would try to put them through. I have heard of a few 14 bolts that came in 1/2 ton trucks with 6 lugs, but those are few and far between. Anybody else?