Rearend ? along with Gear ratios.

[Dan 67 Chevy LWB]

What different rear nds came in the 67-72 trucks? Did it vary depending on if it was an I-6, SBC or BBC. Also what gear ratios were offered.

I have a truck that started as an I-6 and 3 on the tree. If i remember from few years ago when i figured it up, my rearend as a 4.10 gear.

I'm in the process of converting to a BBC. So want to make sure or see if it is best if I change my rearend.

Thanks

[Shyguy]

Is it a 1/2 ton or 3/4 ton?

I am sure that 3.73's were offered in the 1/2 tons with l6, but I am not sure what else was offered.

Danny

[lilred67]

i've only seen 3 different ratio's for 67-72 1/2 ton trucks.
3.08
3.73
4.10

[Longhorn Man]

C/10;
3.07
3.73
3.54 (very uncommon and not in the books)
4.10
C/20
3.54
4.10
4.11
4.56
4.57
5.13
6.something.... does it even matter at these RPMS?
C/30
4.10
4.57
5.13
6.something

[into69z]

If it helps-I installed a rearend out of an 86 3/4 ton that came stock with a 3.23 gear. I too changed to a big block and had 4.10 in my 1969. It runs much better-70mph is achievable and the gas gauge doesn't move as much-but I still average 10-12mpg.

[2tons of fun]

as far as the rear ends them selfs you would have a 12b in a 1/2t leaf or coil. and a rare d60.

a coil 3/4t would have a d60ff

a leaf 3/4t would have a eaton 052

no coil 1t,

1t srw would have either the eaton 052 or 072

1t drw has the eaton 072.

[Longhorn Man]

on 3/4 ton, eaton HO52 was that norm, unless big block was optioned, then the dana. Rear suspention had nothing to do with it.
Then on the one ron, no coils, no dana, just the Eaton HO52. There were some options for the heavy duty c/30, but far and few and pretty much not important to anyone here.

[Dan 67 Chevy LWB]

This is a 1/2 ton with coils.

So more then likely I have a 12 bolt. I guess i will have to climb under the rear and make sure.

That is also good, as i know there is aftermarket parts available for the 12 bolt.

[69GMCLonghorn]

Originally Posted by Longhorn Man

on 3/4 ton, eaton HO52 was that norm, unless big block was optioned, then the dana. Rear suspention had nothing to do with it.
Then on the one ron, no coils, no dana, just the Eaton HO52. There were some options for the heavy duty c/30, but far and few and pretty much not important to anyone here.

Might be a dumb question, but is the "Eaton" rear end also called a "Corporate" rear end? Or are they 2 different entities?

[profe56]

kindergarden question what it means SBC and BBC

[69GMCLonghorn]

Originally Posted by profe56

kindergarden question what it means SBC and BBC

Small Block Chevy
Big Block Chevy

(GEEZ I hope that's right! HAHA)

[profe56]

thank you

[hounddogs!]

Originally Posted by 69GMCLonghorn

Might be a dumb question, but is the "Eaton" rear end also called a "Corporate" rear end? Or are they 2 different entities?

Different entities. Corporate is the 10-12-14 bolt that you see under every Impala/Chevelle/Nova in the world. The Eaton HO52/72 rear is a truck unit with a hemispherical diff cover. It looks like half a basketball with a fill plug installed.

[Longhorn Man]

It is technicly a coperate rear, with an eaton diff. The rear end assembly was built in house, or under a contract specificly for GM while the Dana was built by an outside vendor and sold to other companys in addition to being sold to GM.

[Longhorn Man]

Side note... the car 12 bolt and truck 12 bolt are not quite the same, double check aplications of parts you buy for the truck unit.

[nsuengineer06]

GMC pauls has a pretty good write up on the rear ends that gives the stamp codes and the corresponding gear ratios.. Located Here.

[cparman]

I asked this question in the driveline section, and got an answer, sort of. I want to change the ratio from 3.73 to 3.42. My reading says that I will need a 3.07 carrier to accept the 3.42 gear. Is this correct. I have read here that most do not recommend going to a 3.07 with a 700r4 trans. Don't need a posi, cause my wife thinks I am over driving like I was 16 again. She accused me of that when I had my 500hp Chevelle. I took it as a compliment!

[nsuengineer06]

cparman I have seen this discussed and don't remember all of the specifics, but I do know that you can buy certain gears for different carriers.. I think I saw them in Jegs or Summit, but it will specify which carrier it will fit. For instance say you have a carrier that will take up to a 3.42, but want to put in a 3.73, if you look hard you can find a 3.73 that is MADE to fit the 3.42 carrier.

[cparman]

NSU, I am aware of this with the 12 bolt car rear ends. Just hoping someone can help me spend my wife's 30th anniversary money just once. Dang women just do not understand gear sets. ALTHOUGH they can order 3 tops, and pants on line and send them back 14 times and justify the shipping!!!!!!!!!

[nsuengineer06]

lol yea I know all about that! I thought they had those gear sets for the truck carriers too. I may have been mistaken. Ya know, if you just need somewhere to send that money, I sure need a set of heads for my 327!