What year differentials fit?

Hey,
I'm thinking about going to some steeper gearing in my 94 RMW with tow pak, Thinking 3:23s as I'm not sure I want to go 3:42s as I do some pretty long interstate trips, But any way, my question is this, What year 10 bolt posi differentials will fit in our wagon rear axles?

yor best bet is get a 323 posi from a 91 to 93 tbi wagon. if you are thinking of just swapping out a posi carrier from another 10 bolt make sure it has the correct spline count 30 ,most 10 bolts will be 28 spline.

2.93 to 3.23,. not much difference,.waste of money,.

i like to run 3:73's in my automatic cars,. and they still get better than 23mpg,. and so much nicer to drive,.

If you are not going to swap the entire rear from a TBI car, just buy new gears, and put them in your housing. There is a pinion height setting tool available on Amazon to get the shims right the first time. Then all you have to do is set the lash, and preload on the ring gear. An aftermarket POSI is a better choice than the OEM one as well. While you are doing that, get a set of US made Moser axles instead of the crappy Chinese or Indian ones that are sold by everybody else. The cost difference is insignificant compared to the quality.

phantom 309 wrote:

2.93 to 3.23,.  not much difference,.waste of money,.

i like to run 3:73's in my automatic cars,. and they still get better than 23mpg,. and so much nicer to drive,.

23MPG down hill or at slow speeds maybe but my last trip to NY i drove 913 miles in 14 hrs and 6 minutes, that's 65 MPH average including 2 fuel stops, 22.8 MPG average and I have the receipts to  prove it, Kinda hard to believe over 23 mpg with 3;73 gears in my real world experience

I should mention that's with a brand new opti, plugs wires, cleaned air filter, new fuel filter and low restriction exhaust, and tires inflated to 34 psi. ohh and I forgot to remove the roof racks

after playing around with numbers a 3.73 rear with the .78 OD in our trans gives you an effective rear ratio of 2.90 as vrs the 2.93 I have now, Now I know for sure driving around on the highway in drive with no OD at 2.93 ratio at 70MPH plus I would not be seeing 23+ MPG

Fred Kiehl wrote:

If you are not going to swap the entire rear from a TBI car, just buy new gears, and put them in your housing. There is a pinion height setting tool available on Amazon to get the shims right the first time. Then all you have to do is set the lash, and preload on the ring gear. An aftermarket POSI is a better choice than the OEM one as well. While you are doing that, get a set of US made Moser axles instead of the crappy Chinese or Indian ones that are sold by everybody else. The cost difference is insignificant compared to the quality.

Thanks for the advice fred but I'm really not looking to turn a several hundred dollar job into a thousand dollar plus job, I have a line on a rear out of a 90 tbi caprice and was wondering if the gears would fit.

mtrhead79 wrote:

yor best bet is get a 323 posi from a 91 to 93 tbi wagon. if you are thinking of just swapping out a posi carrier from another 10 bolt make sure it has the correct spline count 30 ,most 10 bolts will be 28 spline.

That's the info I was looking for! Thanks so much!

GMjonn wrote:

23MPG down hill or at slow speeds maybe

but my last trip to NY i drove 913 miles in 14 hrs and 6 minutes, that's 65 MPH average including 2 fuel stops, 22.8 MPG average and I have the receipts to  prove it,

Kinda hard to believe over 23 mpg with 3;73 gears in my real world experience


after playing around with numbers a 3.73 rear with the .78 OD in our trans gives you an effective rear ratio of 2.90 as vrs the 2.93 I have now, Now I know for sure driving around on the highway in drive with no OD at 2.93 ratio at 70MPH plus I would not be seeing 23+ MPG

Kinda hard to believe the 65 mpg average in my real world experience,.which amounts to 40 yrs driving or more,.

Quote :

23 mpg downhill or at slow speeds,.

Thats tantamount to calling me a liar,. and that irks me tremendously,.

I DO have many years of experience driving LT1 vehicles,.the first was a 9c1 in 1999,.i still have that car, and it now has 3 73's,.i have driven every gear ratio from 2:56 down to 4:88's with automatics,.and ratio's from 2:93-4:88 with manual transmissions,.

i,ve built a few lt1's over the years, and put in a few rear ends gear sets and transmissions etc too,.

All my advice and experience is from the real world,. not the internet world,.

you need to also double check your information regarding the 4l60e overdrive ratio,.your info is erroneous,.

Irony alert: Gentlemen, you are both communicating your real world experiences on the internet.

A problem can arise in an assumption that diverse experiences apply in all cases. Mileage in these cars can vary for mechanical reasons other than drive ratios, as well as driver habits. I am one of those drivers who likes to mash on the accelerator. Give me your 23 mpg car and I'll get 17 mpg on I-90 from coast to coast. My wife will set the cruise control and beat my average any day. I loath cruise control. You might as well let someone else drive. My 1995 Caprice with 3.23 ran beautifully and got 22 mpg through tuneups and mods. My 1996 Roadmaster with 2.93 also ran beautifully and got 17-19 mpg, and I never could consistently get better no matter what I changed. I just had Solomon K. tune the PCM on my latest (1996 Caprice, 2.93), and I replaced the 20 yr-old O2 sensors. We'll see what happens.

I f someone is comparing mileage driving through the Appalachian Mountains to someone driving on the flats of Nebraska or Canadian plains or Onrario, I could see a world of difference in mileage.

Personally, I would not doubt what Nick says for a minute. because I've known him for several years.