Hey folks,

I'm trying to get some better gearing and limited slip for my '72 Delta 88 Royale, and trying to find out what cars I can get an axle from that'll be as bolt-on as possible, with either the possibility of upgrades, or already with some 3.23/3.42 gears and limited slip. Right now this 2.56 open diff needs to go. Do axles from any GM B-body work? What are my options? Running out of luck with searches.

TIA,

Dante

 

I have experience with 2 66 big cars. Both have type O 9.3” rear ends. But I’m here to talk about the feel of the gear ratios.

Over past 30 years, I’ve run 2.93, 3.08 and 3.23 gears. My favorite is probably 3.08:1 which was factory for the 98 and an option for the ‘66 Starfire.

I didn’t like the 2.93’s. It felt wrong to have a big block that was slow off the line, even with big cars. I had to put 2.93’s in at some point in my 98 convertible, it was all I could find in the time I couldn’t have it off the road when something back there broke. I have a vague memory from the 80’s with an I5 LA-SF run with better than 16mpg. Might be an optimistic memory.

I ran 3.08’s for a decade or 2. This really seems to me to be the best balance between economy and off-the-line. Olds knew that and specc’d it for years. But I was always curious about what 3.23’s would feel like.

2 or 3 years ago I found NOS 3.23 gears for both Big cars. They’re fun. But the gears have pushed mileage way down. At 60mph, the 455’s are spinning around 2,800 rpm. Mileage went from say 11-13 mpg per tank with 3.08’s down to 9 or so with the 3.23’s. If I knew this prior, I might not have changed them. It could be my carb tuning, or driver habits. I’m still working on that.

Long winded way of saying my humble advice would be enjoy the 3.08’s if you find them. If you don’t mind the mpg hit, 3.23’s are more fun. If you’re beginning at 2.56:1, pretty much every other option will make you happier.

Cheers,
Chris

 

Well the great thing about 1971- 1976 corporate era GM is that ALL the rear-ends from all gm vehicle interchange.
so Impala, Electra, Bonneville Granville Catalina Centurion Riviera 88 98 etc all interchange.
WAGON guts will work but the early ones were Leaf spring.
They had 3 different sizes of rears in this era
10 bolt 8.5 (found in the lower HP cars)
10 bolt cover / 12 bolt ring Pontiac 8.875 (mid powered cars 400 cube 350 4bbl etc)
12 bolt cover/ 12 bolt ring Olds 9.3 (found in most 455 cube cars and wagons)
So you do have many choices IF you can find these BIG cars.

Around here in Ohio...They are GONE... Demo derby guys ate them all up here.
10 bolt 8.5 would be your best choice to get any ratio you want.
They are used in trucks so i would think in a car you could get some good life from them ... I think I have 2 housings on the shelf from an Impala
I saved them to build for the BIG tired Cleveland guys with the wagon wheel cars...lol.

Jim
J D

 

My 1971 Royale convertible was a 455 2-barrel, it had the 10 bolt (8.5). I have a 1971 98, with the "BIG" 4 barrel (inside joke) it has the heavier 12 bolt. So first I'd find out which rear housing you have. The 10 bolt would be easier to find better gears, imo.

 

Looks like I'll be hunting an Impala diff then. I wanna be able to get an aftermarket posi unit with better gears. At this point if I can get a complete diff that's usable I'll be in good shape.

I have the 12 bolt cover, 12 bolt ring. There are literally no options out there. I'd like first and foremost posi, secondly a better gear.

 

Remember with this rear... the gears and posi go together. and is that way with most GM rears.
Carrier breaks on the carrier make it only carry certain ratios ...so watch what you buy and make sure it will be for the ratio t=you want or intend on finding. Jim

I think I have a Posi 2.93 ratio for the 12 olds 12 ring 12 cover. 1971 -1976 era. or it might be the old one. All reconditioned ready to go... 31 spline as all were but the difference is the early 65-70 were 30 degree pitch spline and the 71 -76 were 45 degree spline pitch on the axles.
I will check if you are interested.

 

Sent you a PM.