I'm about to go through the differential out of my '71 Supreme Convertible. As expected, it's the dreaded 2.56 ratio. It is my understanding that the carrier won't accept a gear swap without a spacer and longer bolts. I really want to put a limited slip unit in anyway, so I'm I correct that the housing (stamped R6 if I remember correctly) will be fine and if I'm going to change carriers then the whole 2.56 stock carrier problem doesn't matter? What I'm hoping is that my housing will work fine with a limited slip (Eaton or other) and 3.42 gears. Thanks for any advice!

 

Yes you will need a new carrier and obviously the gears...

What are you going to do with the 2.56.....I may be interested

 

I won't have any use for the gears or the carrier. It would make someone a very servicable replacement as my car has only 57K miles and ran beautifully prior to disassembly.

 

You are lucky to have the 10 bolt 8.5 as the parts are pretty readily available.

eaton
dura grip eaton
true trac
auburn
factory reconditioned units are all available

3.08 3.23 3.42 3.73 3.90 4.10 4.56 4.88 and on are gears out there new and used.

If you need a quote on parts PM and will give you something to start with your search. Jim

 

People really want those 2.56's? I've been sitting on a set for a bunch of years now. I figured that it'd be fun to swap out the 5.00's in my W-31 and see what she'd do for top end. The 5.00's only let her get up to 105. I don't know if I'd want to be putting all the extra strain on that aluminum carrier though. : )

 

I have a 2.56 in my conv. It is going to stay. I want a nice cruiser. Right now she purrs down the road 60 to 70 no problems.
Larry

 

Oh, I understand Larry! I actually bought my car in Tampa and drove it home to north of Birmingham, AL ... over 700 miles. Not only did it drive beautifully on the Interstate, but it got fantastic economy as well. That said, it's undergoing a body-off restoration and the days of roadtrips are over. A little around town and that'll be about it. I've done an extensive rebuild of the 350, which appears stock other than the intake, but it isn't stock . That, mixed with the 3.42 gear should wake it up a little!

 

The 2.56 ratio may not impress your buddies, but chicks don't seem to mind the one in my Olds

... just teasing

 

The 2.56 works great with a TH-400 with a 2.75 low gear set...I wouldn't trade my 2.56 for anything....

 

The freeway gears do better smoking on the burnouts because the tires are actually spinning at a higher rate of speed. NOT rpm SPEED. Look at your speedo and you will see what I mean. lol. The motor will not even be working up a sweat and the tires will be smoking like crazy... Jim

 

You go from 2.56 to 3.42 you won't be waking it up a little. It will be like hitting Big Foot with a stick when he's a sleep. You better run.

 

Hey I ran a 13.89 @ 97 MPH with 2.56 gears (at the top of second gear). I just shifted into 3rd when I went through the traps. Don't knock em too hard. And that was with a J headed 455.

 

Just obtain another diff assembly and upgrade that to the ratio of choice.
Then put the 2.56 one back in the closet in case you ever want to continue your road trips!
However, posi is almost a must with these cars, even with the 350s.

Don't some of the stock GM truck gears / carriers fit into these units?? I heard rumors...

 

Most of the trucks with 8.5's have the gov-lock posi unit,which is equivalent to a grenade with a loose pin.

You will be very happy with a 3:42 in your car.You might even get better mileage than you do now.Your gear is a torque multilier.Having a 2:56 is like having it chained to a brick wall.Not as easy to get going,but runs at a lower rpm when cruising.It just takes a little more squirt to get it moving.The 3:42 will be better all around.

If you need help finding parts,I have plenty,new & used/rebuilt.

 

Interesting topic. I've been wanting to pep up my Cutlass, guess I better see what's in it now.