Differential Gear Options

[KrAxRACING]

I've got a '94 RMW. Non tow package so a 2.56 rear end. I'd love a much better gear ratio in it, something in the 3's. Does anyone know what specs of a gear i'd need and what you could find one out of?

 

[GMjonn]

93 and earlier tow cars had 3.08's, that would require a adjustment of the pcm.

 

[uvaldi]

I went with 3.23 new take-off gears from a Chevy truck. Alot of guys like 3.73 but I want maximum top-end and decent gas mileage. Any 10 bolt 8.5 chevy rear with 30 spline axles I think? You might want a posi set-up too. You will need a different carrier also. I put in all new components except the carrier. It took me months to find all USA made stuff. Bearings, gears, shims..etc and of course a 3.23 reluctor ring for ABS. It was alot of work but worth it. Your car will not lug at highway speeds anymore and be way more reponsive. Someone else will chime in with the what series carrier you want and the spline count. I can't remember. I used a old Hypertech programmer to fix the speedo for the new gear ratio. Uvaldi.

 

[KrAxRACING]

What's the pcm? Shouldn't the speedo not be effected or is it measured by rpms/gear? this isnt just as simple as finding a gear that fits properly and swapping it out? i would need a new carrier for another gear or for the posi? it just about spins tires pretty decent now with 2.56 and no posi. i can imagine it'd just burn all the way to 3rd gear if i had 3.77's on and the tires i have now.

 

[MrBuick (Magnum)]

The 2.56's use a series II carrier. The head on the pinion is HUGE, it forces the ring gear to get moved farther to the outside. 2.73, 2.93, 3.08, 3.23, 3.42, 3.73, 4.10, 4.56, etc all used a series III carrier. The 94-96 tow pack wagons used a 2.93 gear ratio with a posi optional. Most of them got it, but not all. 91-93 used 3.23 in the tow pack wagons. Posi was optional on them. Not a TON got a posi with it, but some did. You can force a sedan axle to fit, but it's not smart. It's cheaper/ easier to get an entire rear, and replace bearings vs having new/ used gears setup.

I'm looking for a 3.23 rear end for my wagon. I want more off the line, but I still drive it at 80mph+ on the freeway. Hell, even a 2.93 axle is a huge improvement over the pathetic 2.56's.

The PCM controls the engine, and the tranny. It takes an imput from the tranny out put shaft. Then it multiples this signal for what it sends to the cluster. The PCM needs an adjustment for a gear swap because the tranny output shaft is spinning a different speed for the same axle shaft speed. In the pre 94's, this was done with a different little gear on the output shaft of the tranny. But 94-96 is all electronic.

 

[KrAxRACING]

Hmm I guess I should know by now life isn't nice and easy haha. I don't know much about powertrains. I believe the rear is a 10 bolt which is the one thats supposedly bullet proof? Is a series III carrier also 10 bolt? Posi has clutches or something to that level inside?? There was a 90-92 something Chevrolet Caprice wagon at a junk yard just down the road from my house. What do you suppose that might have in it? Or if I went to the junkyard, and inquired about a truck rear end, do you know any truck rear's that would slip right into the RMW? They'd more than likely have a good 3 something in them with limited slip anyways.

 

[uvaldi]

Nothing is bulletproof. But the chevy 10 bolt is tough. I don't know crap about the wagon axle differences. Just find a wagon axle is the junk yard and then decode it from the axle or option codes. Or if you have the money just build the rear end guts up yourself with new parts. If it was my wagon I would go with 3.42's with all new gears and bearings and posi. The car will then actually not spin the tires as much because more power will be getting to the ground.

 

[KrAxRACING]

I think I meant 12 bolt, but yes either way.

I talked to a buddy, and he believes his friend is selling a 1990's something, chevy 1500 rear end. Would that fit in the RMW? Any idea what they would have for gearing?

 

[KrAxRACING]

My friend is selling a 10 bolt rear end out of a G or maybe F body. would it fit into my RMW? 28 spline 3.73 posi. Easton? Carrier

Complete with drums, how much shouldni be paying for it if its in decent condition?

 

[Ancient_1]

The wagon rear is unique to the wagons. Others are not a bolt in, as Cory said even the sedan rears are not even tho can be forced (I tried it on my 80's Electra Estate but had clearance issues with the drums and frame). Most all 10 bolt internals are compatible as long as you have the right carrier and spline count for the axles. So as Cory said the wagons have 30 spline axles and will need a carrier setup for that.

 

[KrAxRACING]

What vehicle do people know the rear end fits into the RMW? Theres a bunch of people on here who have it done. Do they use the tow package rear end and swap gears? Will the impala SS fit into the RMW? What are the basic specs of a rear end that ill need? 30 spline, series III carrier?

 

[95 Roadmaster]

I've got a '94 RMW. Non tow package so a 2.56 rear end. I'd love a much better gear ratio in it, something in the 3's. Does anyone know what specs of a gear i'd need and what you could find one out of?

I know the conversation has shifted some, but to answer this question, you need to know what you want. Is it power, or mpg's, or both? I have the exact same RMW, with the same puny 2.56 gear. I purchased a used 3.08 posi gear from someone with an old B-body Caddy, but have yet to put it in.

I have learned some math, that might be helpful for you to decide what gear you want. I wanted something a little bigger (numerically), but I still want mpg's, so I didn't want to go too big. If you use your HVAC control, and go to the rpm display (I forgot which number it is). You will see when you're doing 70 mph, you will be at 1500 rpm. I'm using 70 mph, as the benchmark, as that is the average highway speed I drive. With a 3.08 gear, you will be doing 1804 rpm at 70 mph. You should have a drastic improvement in acceleration, but still be under that magical 2000 rpm range at highway speed. Here's how you do the math:

1500 rpm (what you are doing now @70 mph), times the gear ratio you WANT to go with. So, 1500 x 3.08 = 4620. Now, take that number, and divide it by the gear you currently have. So, 4620/2.56= 1804. That is the rpm you will be doing with the NEW rear end, at 70 mph. I know it seems a little backwards, but the math works!

Obviously, you can do the math at any given rpm, for any given speed. Like I said, I use the benchmark of not going over 2000 rpm at 70, for highway mpg's. I had 2 Mustang V-6's, and they both did 70 at 2000 rpm, and got respectable highway mpg's (close to 29). On the flip side, I also owned a 2002 ZR2 Blazer, that also did 70 at 2000 rpm, but the gas mileage sucked! I always wanted one of those 4.3 V-6's, but now, forget it!! That thing was a PIG!!

John

 

[KrAxRACING]

Hey John. Thanks for the response. Thats quite the hike in RPMS. We were thinking at best 3.73-3.77. Its now our 3rd vehicle and only used to bring my go kart to the race track a couple times a month ( 30 mins one way) as well as delivering large items or number of items. Either way were not really worried about mileage with it anymore. Weve already had our trip to florida with it back in 2001. Achieved 31-32 mpg at best fully loaded car on that trip at best.

At 60mph it turns 12-1300 rpms
On average and i guessed before a 3.7 range would bump it to atleast 1800 rpm or probably at 2,000?

 

[95 Roadmaster]

Hey John. Thanks for the response. Thats quite the hike in RPMS. We were thinking at best 3.73-3.77. Its now our 3rd vehicle and only used to bring my go kart to the race track a couple times a month ( 30 mins one way) as well as delivering large items or number of items. Either way were not really worried about mileage with it anymore. Weve already had our trip to florida with it back in 2001. Achieved 31-32 mpg at best fully loaded car on that trip at best.

At 60mph it turns 12-1300 rpms
On average and i guessed before a 3.7 range would bump it to atleast 1800 rpm or probably at 2,000?

HOLY S**T!!! You really got 31-32 mpg's? WOW!!! That's amazing!! I wish I could get that! The most I've been able to get, is 21 mpg!

Anyway, after doing the math, if you went with a 3.73 rear end (I know that sounds like a Ford, but that's the only number I know!), you would be doing 2185 rpm at 70 mph. Still not bad, but you better get a posi unit, as you'll be smoking that right rear tire off at every intersection, if you don't!! And, with a good receiver hitch, you'll be able to pull anything you want!

John

 

[KrAxRACING]

My dad calulated it. Not too bad for rpms. And ya thats for sure. So what do i need spec wise thatll fit right in? Any B body rear end with 30 spline series III? What trucks fit for sure?

 

[G-136991]

My friend is selling a 10 bolt rear end out of a G or maybe F body. would it fit into my RMW? 28 spline 3.73 posi. Easton? Carrier

Complete with drums, how much shouldni be paying for it if its in decent condition?

G body is coil sprung F body is leaf springs

 

[G-410547]

I was told I have to find a reluctor wheel to change mr gear ratio to 373

 

[Chicken John]

I know the conversation has shifted some, but to answer this question, you need to know what you want. Is it power, or mpg's, or both? I have the exact same RMW, with the same puny 2.56 gear. I purchased a used 3.08 posi gear from someone with an old B-body Caddy, but have yet to put it in.

I have learned some math, that might be helpful for you to decide what gear you want. I wanted something a little bigger (numerically), but I still want mpg's, so I didn't want to go too big. If you use your HVAC control, and go to the rpm display (I forgot which number it is). You will see when you're doing 70 mph, you will be at 1500 rpm. I'm using 70 mph, as the benchmark, as that is the average highway speed I drive. With a 3.08 gear, you will be doing 1804 rpm at 70 mph. You should have a drastic improvement in acceleration, but still be under that magical 2000 rpm range at highway speed. Here's how you do the math:

1500 rpm (what you are doing now @70 mph), times the gear ratio you WANT to go with. So, 1500 x 3.08 = 4620. Now, take that number, and divide it by the gear you currently have. So, 4620/2.56= 1804. That is the rpm you will be doing with the NEW rear end, at 70 mph. I know it seems a little backwards, but the math works!

Obviously, you can do the math at any given rpm, for any given speed. Like I said, I use the benchmark of not going over 2000 rpm at 70, for highway mpg's. I had 2 Mustang V-6's, and they both did 70 at 2000 rpm, and got respectable highway mpg's (close to 29). On the flip side, I also owned a 2002 ZR2 Blazer, that also did 70 at 2000 rpm, but the gas mileage sucked! I always wanted one of those 4.3 V-6's, but now, forget it!! That thing was a PIG!!

John

I know the conversation has shifted some, but to answer this question, you need to know what you want. Is it power, or mpg's, or both? I have the exact same RMW, with the same puny 2.56 gear. I purchased a used 3.08 posi gear from someone with an old B-body Caddy, but have yet to put it in.

I have learned some math, that might be helpful for you to decide what gear you want. I wanted something a little bigger (numerically), but I still want mpg's, so I didn't want to go too big. If you use your HVAC control, and go to the rpm display (I forgot which number it is). You will see when you're doing 70 mph, you will be at 1500 rpm. I'm using 70 mph, as the benchmark, as that is the average highway speed I drive. With a 3.08 gear, you will be doing 1804 rpm at 70 mph. You should have a drastic improvement in acceleration, but still be under that magical 2000 rpm range at highway speed. Here's how you do the math:

1500 rpm (what you are doing now @70 mph), times the gear ratio you WANT to go with. So, 1500 x 3.08 = 4620. Now, take that number, and divide it by the gear you currently have. So, 4620/2.56= 1804. That is the rpm you will be doing with the NEW rear end, at 70 mph. I know it seems a little backwards, but the math works!

Obviously, you can do the math at any given rpm, for any given speed. Like I said, I use the benchmark of not going over 2000 rpm at 70, for highway mpg's. I had 2 Mustang V-6's, and they both did 70 at 2000 rpm, and got respectable highway mpg's (close to 29). On the flip side, I also owned a 2002 ZR2 Blazer, that also did 70 at 2000 rpm, but the gas mileage sucked! I always wanted one of those 4.3 V-6's, but now, forget it!! That thing was a PIG!!

John

I have a '94 sedan with the same lackluster 2.56s, do 3.08 swap right in or do I need a whole different rear end?

 

[BuickGirlFromMars]

T

I have a '94 sedan with the same lackluster 2.56s, do 3.08 swap right in or do I need a whole different rear end?

The 10 bolt has a carrier break at 2.56 so you’d need a new carrier to do anything numerically higher