Rear diff compatibility

[Matt68]

I have a 1973 Barracuda with a 727, currently a 741 case rear diff. I've located a rebuilt 489 case rear diff with 3.55 gears and sure grip. Owner says it was out of a 1970 Charger. My question is will my axles fit without issue, and what will I need to change on my yoke.
TIA

 

[Ricks72Chlgr440]

I have a 1973 Barracuda with a 727, currently a 741 case rear diff. I've located a rebuilt 489 case rear diff with 3.55 gears and sure grip. Owner says it was out of a 1970 Charger. My question is will my axles fit without issue, and what will I need to change on my yoke.
TIA

The axles will fit either one without issue. The yoke may be the same as you currently have but you'll need to check that. When I upgraded my 8.75 to a Dana 60 I had the local driveshaft shop change the pinion to the larger one. Not a big deal.

 

[Chryco Psycho]

Changing the Yolk on a 489 can require changing the crush sleeve or replacing it a using spacer & shims , so yes it is a big deal , there are conversion U joints if the driveshaft & yolk are different so you can leave the yolk alone .

 

[Xcudame]

This is the "adapter" u-joint Chryco mentioned. That's the way I'd go for any mismatch between the drive shaft and yoke.

Moog Chassis Parts 347 Moog Premium U-Joints | Summit Racing

Free Shipping - Moog Premium U-Joints with qualifying orders of $109. Shop U-Joints at Summit Racing.

www.summitracing.com

 

[MoparCarGuy]

The axles will fit either one without issue. The yoke may be the same as you currently have but you'll need to check that. When I upgraded my 8.75 to a Dana 60 I had the local driveshaft shop change the pinion to the larger one. Not a big deal.

Rear Differential:
To be clear, the 8-3/4" rear differential also known as a "chunk" or a carrier with a 741, 742, or 489 case will fit your existing rear axle housing and will work with your 1973 E-Body rear axles.
The rear axle spline counts are the same.

Rear Axle Housing & Shafts:
The 1970 Charger (B-Body ) 8-3/4" rear axle housing is ~55.000" wide which is 1.5" narrower than an E-Body 8-3/4" housing (~56.500").
The axles themselves from a 70 Charger 8-3/4" rear will NOT fit a 1973 E-Body 8-3/4".
1970 B-Body axle shaft length 29-3/16" (narrower than E-Body).
1970-74 E-Body axle shaft length 29-31/32".
Factory axle shafts are 30-spline for all 8-3/4" Rear Differentials/Housings.

@Ricks72Chlgr440 is correct for your differential question and yoke verification (see U-joint chart below).

Just want to make sure others understand the axles themselves differ in length.

SOURCE: Mopar Action magazine Tech Archive on moparts.com

 

[Avalanche]

Great info

 

[Matt68]

The axles will fit either one without issue. The yoke may be the same as you currently have but you'll need to check that. When I upgraded my 8.75 to a Dana 60 I had the local driveshaft shop change the pinion to the larger one. Not a big deal.

@Ricks426 the guy selling the 489 diff said that there is a possibility that the spline count on my '73's axles might not match up on the spline count on his 489 diff. True? I just assumed that all 8.75 diffs had the same spline count axles going into them all. Is the guy wrong?

 

[Matt68]

@MoparCarGuy So, just to be clear, an 8.75 rear diff, regardless of year and application, will fit my '73 Cuda. The only issue will be the driveshaft length and yoke spline count, correct? If it doesn't match my driveshaft/yoke, I'll need to get an adapter, but then it should be all good?
TIA

 

[MoparCarGuy]

Yes, any of the 8-3/4" differentials (carriers) will work in your 1973 Cuda's 8-3/4" housing.
The axles are all the same spline count. Only the length of the axles changes to match the housing width.
The driveshaft length should not change. The U-Joint and yoke combination can vary so read the below and just measure your current U-joint and the yoke of the Charger 489 carrier you plan to use. Hopefully, you will not need a 7260/7290 conversion U-joint at all.

Info below pasted from the Guide to the Chrysler 8-3/4″ by Gary Lewallen, January 1998 LINK
There are four different yokes that have been used with the 8-3/4″ axle for the ‘7260’ and ‘7290’ style universal joints. The ‘741’/’742′ assemblies used a coarse spline (10 splines) drive pinion. Most of the aftermarket gears also use this coarse spline yoke mount. There is a small yoke for the ‘7260’ and a larger one for the ‘7290’. The ‘489’ assembly used a fine spline (29 splines) yoke. Note: during the phase-in period of 69-71 for the ‘489’ unit, there were several permutations of pinion size and yoke availability. 69-70 ‘489’ units may be equipped with a coarse (10) spline pinion, particularly for the ‘7290’. There are two yokes for the ‘7260’ and ‘7290’ universal joints with fine (29) splines.
Interchange Notes:
7260 & 7290 yokes may be interchanged if the pinion spline count is the same.