8.25 Gearing and Posi

[Theupperlowdown]

I'm sure this has been talked about before but having a hard time finding cohesive answers to all my questions.

I have a 1974 Dart 8.25 Rear with 2.71 and an open diff. This isn't a race car, it's a street car. It will see highway at times but I'd like to turn some tires when I'm in the mood. I also don't want to spend $$$$.

So I would like to put together a 3.21 Posi set up in that housing. I do know the carrier bearings changed in 76. What I'd like to know is can I run a set of used 3.21s out of say a 1978 Dodge on a Yukon Posi for this rear end?

I do have a line on some 3.21s for $125 but the owner is saying they only fit 1976 and up. I know the ring bolts much later are metric and some after market rings are dual drilled but why wouldn't a 1978 ring and pinion fit in a 1974 housing?

A further reach... and I think I know the answer to this, but does anyone make a kit to put a 90's Jeep 8.25 posi in a 75 or earlier housing?

Very new to Mopar and happy to be here.

Thanks Guys!

 

[Professor Fate]

A few things you need to keep in mind:
There were 2 different gear carriers used in the 8.25- one for 2.45 and 2.21 ratio gearsets, and a different one for 2.71 and lower (higher numerically) gearsets. They are not interchangeable.
The axle spline count changed from 27 spline to 29 spline sometime in the late '90s.
The carrier bearings' outer diameter changed sometime during the life of the 8.25 (I want to think mid/late '80s?). The early bearings can be used on a later carrier.
So, here's what you need to find-
(SureGrip) carrier and gears (don't forget to pull the pinion gear and any spacers used) of the proper gear range, up to the mid/late '90s from any of the following (there may be others) with an 8.25:
A/B body Mopars
Early Dakotas
Light duty pickups and vans
Jeep Cherokees (Make sure it's an 8.25- Jeep Cherokees also used other diffs like the Dana 30, 35, and 40; and the AMC 35 that can easily be mistaken for a Chrysler 8.25)
And as a side note, if it comes out of a Mopar, grab the speedometer drive gear and housing out of the transmission while you're at it- then your speedo will read correctly, depending on tire size...

 

[AJ/FormS]

What engine?
Jus Asking?
My guess is she's a heavy 318, A/C car with all the trimmings,

If that's true;
1) your first purchase should be a higher-stall convertor, something like a 2800, cuz those 74s were turd-engines. and 18% more gear, just means yur into Second sooner and back in turd-land.
2) your second install should be a small 4bbl.
3) now yur ready for gears,
But 18% more gear, points to 9% worse fuel economy.

Your call.

 

[junkyardhero]

The axle spline count changed from 27 spline to 29 spline sometime in the late '90s.
The carrier bearings' outer diameter changed sometime during the life of the 8.25 (I want to think mid/late '80s?). The early bearings can be used on a later carrier.
So, here's what you need to find-
(SureGrip) carrier and gears (don't forget to pull the pinion gear and any spacers used) of the proper gear range, up to the mid/late '90s from any of the following (there may be others) with an 8.25:
A/B body Mopars
Early Dakotas
Light duty pickups and vans
Jeep Cherokees (Make sure it's an 8.25- Jeep Cherokees also used other diffs like the Dana 30, 35, and 40; and the AMC 35 that can easily be mistaken for a Chrysler 8.25)
And as a side note, if it comes out of a Mopar, grab the speedometer drive gear and housing out of the transmission while you're at it- then your speedo will read correctly, depending on tire size...

the spline count changed "about" mid 1996... so mid 95 and up is the 29 spline stuff. don't be fooled by 6 lug or 5 lug patterns-- 27 spline units can be either!

a lot of cherokees came with limited slip units. the 4 bangers got 4.11's even. 3.55's are very common on dakotas, especially extended cabs for some reason.

 

[townsend]

For rear wheel passenger cars with 8 1/4 the bare carrier with no bearings or ring gear is the same from 73 thru 89 #2881423
Must use a carrier with 2.71, 3.21 or 3.55 ratio ring and pinion.
1981 was the last year for the 3.21 in passenger cars.
Also in some years the 2.94 was an option.
For carrier bearings, just buy the smaller bearing that was used in your 1974.
Some trucks with 8 1/4 were the same as passenger cars thru 1986 with the 3.21 option.
All of the above could be ordered with sure grip.
Professor Fate has covered later models.

 

[Theupperlowdown]

Thank you gents! This is exactly the info I was looking for. I can already see how helpful this community is going to be.

 

[Theupperlowdown]

@AJ/FormS

You are correct it is a 318 A/C car. Currently a full time resident of turd-land lol. I’m tackling the rear end first because I’m rebuilding the rear leafs a redoing some brake lines. I do have a 360 block on a stand that will receive a mild build over the winter and everything you mentioned will get dialed in at that point. Just got the car a couple weeks ago so I’ve got to start somewhere.

 

[JDMopar]

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