Rear Gear options

[OJ1988]

Looking to improve milage on my truck. It currently has the factory 3.73 rear gear set.

I would like to try and find a numericlly lower gear to swap in to help improve milage. Ideally, I would like to pull a complete rear out of another truck and swap it. There are a few 67-72 models in a local scrap yard. Before I go pulling covers, what other gear sets might I find installed in one of these trucks?

[68Stepbed]

The only options for a 67-72 with a 12 bolt was 3.07, 3.73, and 4.11 gears. 73-up could be found with 3.4 but they won't bolt right in.

If you were closer, I'd be willing to trade my 3.07 for what you have now.

[Coley]

Ok, this should be pretty easy.
First, the 1/2 tons (V-8's) came stock with a 3:07 ratio. If there is/was an alternate rear end in the truck it would be listed (99%) on the SPID in the glovebox as an option.....ie: 3:73 or 4:11.
So if you find a truck in the boneyard that has the SPID in the glovebox....you should be able to determine if it was a V-8 truck and if it was optioned with something other than the stock 3:07.
Note: make sure the truck is the right years for your truck relative to the 6 bolt or 5 bolt lug style.
Good Luck
Coley

[OJ1988]

3.07 might help with milage a bit. Would like to get a wider rear, but then I'd be 5 lug right?

Was there a wider 6 lug?
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[Mike C]

What size tire do you have in the back? The easiest thing to do is put a 31" tall tire on it. (265 75 15 currently on the back of my '69 short bed with 307 in it.) That helps a bunch. If you have 28" tall tire now that will take 10% more gear out of it. Making the 3.73 effectively a 3.36. And if you have 26" tall tire the gears will be effectively 3.07.

Obviously, this is an easily reverted swap so you can play around with it to find exactly what you like. 2.73 gears could be found in some 73-82 trucks with the 12 bolt which would drop it even more than the 3.07 but acceleration would be pathetic at best IMO.

[Already Gone]

I piked this up last week for my BB . Its 3:08 Posi from a 71 and I'm replacing my 3:73's hoping to improve my gas mileage.

[OJ1988]

Good find!

AS to the tires, I am runing brand new 235/60/17's in all four corners, would rather not change them at this time.

I am running a wide ratio muncie, so I think acceleration will still be ok with a 3.07 rear. I'll have to see what I can find in the scrapyard.

[PanelDeland]

Wait a minute.Big question is ,where is that info from.To the best of my knowledge(questionable at best)
Auto came with 3:08-07
manual came with 3:73
Options were different for different wight ratings.

If you want better milage and are running an auto trans,I would suggest looking at the 700R4 or one of the electronic OD's.
For a standard,the 5-6 speeds would be a good choice.
The auto OD with a 3:73 seems to be the choice most prefer.This keeps your low end "grunt" while letting the rpms stay down on the hiway.
As stated above,the tire size can give you quite a bit of adjustment.

The real question is "What are you starting out with?"

[OJ1988]

Originally Posted by PanelDeland

The real question is "What are you starting out with?"

As stated in my first post, I am starting out with a 3.73.

Looking at gears for a cheap option to improve milage.

A 5 or 6 speed would be cool, but spending $2000 to save a couple bucks on gas is not the best option imo.

I am looking at small things to improve milage.

[Already Gone]

Originally Posted by OJ1988

As stated in my first post, I am starting out with a 3.73.

Looking at gears for a cheap option to improve milage.

A 5 or 6 speed would be cool, but spending $2000 to save a couple bucks on gas is not the best option imo.

I am looking at small things to improve milage.

Thats why I am going to a 3:08 instead of an ideal 700R4, cause its a lot cheaper to swap the rear end than a trans.
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[68Stepbed]

Since you're running a Muncie, I'd just install 3.42 gears. The 3.07(3.08) will be a bit of a dog with the 4-speed, especially on any incline. When my dad built his 56, he put in an M20 Muncie and a Ford 9" from a T-bird with 3.00 gears. It did ok on flat surfaces, but he almost burnt the clutch up pulling onto an alignment lift, so he switched to 3.70 gears.

The 3.73s in your truck now are actually the ideal gear for a manual trans, but if you really want to better your rpm range, I would go no higher than 3.42. This means you most likely won't find a ready to swap in rear. You will be better off changing just the ring and pinion set.

[67chevemall]

I have a ring and pinion and carrier in a box that are 3:07's,,,drop right in...

[OJ1988]

It pulls pretty hard with the 3.73 and Muncie. I go through the gears pretty quick when driving. I'm sure 3.07s would slow it down some, but I think I'd be ok. It's not my hot rod anyway.
Im gonna look around. Not wanting to swap just ring and pinion now, I'd like to put a posi in ot if I had it apart. But that's more cash.
Right now I want to fine tune it and get some more mpg's.
There's a place selling a 4th gear overdrive gear set god the munice, that might be cool, but a lot of cash too.
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