Hi olds people! I am wondering, I have a 1970 olds cutlass with the W-31 package. My rear gears are the 3:91's. What would be a good all around gear to put in it so it's more driver friendly on the highway, but I still keep some snap? I can't afford another new tranny for it currently, so a gear swap is what works for me at this time. And of course one that I won't have to put in a new carrier. Some of the research i've done on it says I can only put a 3:08 or 3:42 in there with out having to do some extra work.Thanks everyone.

 

i wouldnt go higher than 3.08 and 3.23 will give you decent mileage and not bad rpm on the highway... i like the 3.08

 

I could be wrong but I don't think anybody makes the gears for the O type rear end that's in your car. You can try with Jim, monzaz here on CO, I know he had some that he was selling.
Jim's website

 

your only option without changing carriers is 3.42
I have a buddy with a 70 442 convert with 3.42 and he drives it alot, including the 4 hour trek up to Stanton, MI for the Pure Stock Drags. no issues.
I believe FabCraft in Texas is now making 3.42 and 3.91 Type O gears. There was a thread on here about it. FabCraft is a good place, I've talked with Brad several times.

 

Hollander says that 5.00, 4.66, 4.33, 3.91, and 3.42 were used with the carrier you have; 3.23 & 3.08 used another carrier; and 2.78 & 2.56 was yet another. The axle housing should accept all three carriers. Be very careful if you haven't yet installed a gear set. It's easy to mess up.

 

My niece's '68 4-4-2 has the M21 close ratio transmission and she has a 3.42 posi. That works pretty good for "snap", plus the gas mileage is somewhat better. I like that combo.


Randy C.

 

How tall are your back tires? If you are currently running a 26" tall tire moving to a 28" tall tire will knock about 250 RPM out of the cruise RPM. Might be worth considering prior to swapping gears.

 

What motor and trans are you running?
Around here, you can typically find good used rear ends cheaper than a gear change. As long as the gears are good, new seals, brake rebuild, and you can have it swapped out in a couple hours. Then sell the old rear.

 

If he is gonna do all that, might as well look for a 71/72 rear end for which the parts are readily available.

 

So you are telling him to sell off the numbers matching 3.91 rear end from a real W-31....is that your advice?

 

lol, not exactly....
I didn't see any info on numbers matching, engine, trans etc..
Maybe I should have suggested a chevelle rear?

 

Me personally, I would keep the rear thats in it and get a bigger gas allowance. The RPMs won't hurt anything.