489,741 or 742, the Difference?

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69cudaownr

69cudaownr

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I have a 69 Barracuda with the original 7 1/4 rearend that I want to get rid of. I also have an 8 3/4 housing and axles without the center section. When I see center sections offered for sale they state different casings such as 489, 741 or 742.

What center section should my A-Body have in it? Does it matter?
 
The 741 is correct for the A body, but it does not matter. Any of them will work fine.
 
Yep, the 489 is considered the strongest due to a larger diameter pinion gear stem, but in all honesty any of them will be just fine in your A Body - unless you have more than 500 hp and are launching at the drag strip on slicks, in which case it is not normally the pinion stem that fails anyhow.
 
d55dave said:
Yep, the 489 is considered the strongest due to a larger diameter pinion gear stem, but in all honesty any of them will be just fine in your A Body - unless you have more than 500 hp and are launching at the drag strip on slicks, in which case it is not normally the pinion stem that fails anyhow.
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eh...sorry. 742 is considered the strongest. The 489 pinion has a SLIGHTLY larger OD, but that tapers down to a narrower section, than the 742 diameter. Therefore....the 742 is stronger. It is also easier to set up without the taper.

I believe the 440 six-pack and Hemi cars in the late 60s all had factory 742s, until 489s came in....(69???)
 
With a crush sleeve eliminator kit, the 489 case becomes damn near bomb proof!!
 
found some notes:

8.75" Axle Carrier Types and Years of Production

''741' Casting - 1 3/8" (1.375" Small Stem Pinion.
Carrier casting numbers were 1820657 (1957-1964) and 2070741 (1964-1972). This unit was usually used in low weight/medium horsepower and high weight/low horsepower applications. Although it is the weakest of the 8.75" units, it is still a stout unit, and is stronger than the Spicer-built Chrysler 8.25" rear. The 1 3/8" pinion is also larger than the pinion in the Ford 9" rear.

''742' Casting - 1 3/4" (1.75" Large Stem Pinion.Carrier casting numbers were 1634985 (1957-1964) and 2070742 (~1961-1969). This assembly was replaced by a phase-in of the 1-7/8" pinion '489' casting starting in the 1969 model year. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Although not generally considered to be stronger then the '489' carrier, the '742' carrier is extremely stout, and is favored by many Mopar enthusiasts because they are easier to set up. Noted Mopar enthusiast John Kunkel mentioned that the biggest advantage of the 742 carrier is that it has the largest rear pinion bearing of all the 8 3/4" carriers. The larger bearing helps to prevent pinion deflection better under a load than the others.

'489' Casting - 1-7/8" (1.875" Tapered Stem Pinion Carrier casting numbers were 2881488 or 2881489 (1969-1974). This assembly was introduced in 1969 and was phased-in to relace the 1-3/4" pinion '742' unit through 1970. Note: the 1-3/4" pinion also appeared in some '489' carriers during this period. By 1973, the '489' was the only unit available in passenger car applications, and was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. This carrier is considered to be the strongest by some Mopar enthusiasts. Because it requires a crush sleeve to set bearing preload, some Mopar enthusiasts prefer the '742' casting. This is not really an issue now because there are now parts available to eliminate the crush sleeve.


Carrier Identification:
All 8-3/4" carrier assemblies can be identified externally by the casting numbers. The casting numbers are cast onto an ID pad on the driver's side of the carrier just behind the 'snout' of the case where the yoke attaches to the pinion. In addition to the casting numbers:

The '741' will usually have a large 'X' cast on the left side
The '742' will usually have a large '2' cast on the left side
The '489' will have a large '9' cast on the left side.
 
swing69 said:
eh...sorry. 742 is considered the strongest. The 489 pinion has a SLIGHTLY larger OD, but that tapers down to a narrower section, than the 742 diameter. Therefore....the 742 is stronger. It is also easier to set up without the taper.

I believe the 440 six-pack and Hemi cars in the late 60s all had factory 742s, until 489s came in....(69???)
Click to expand...

:happy1:
 
D55Dave: just adding more info. I didn't mean to sound like a know it all. sorry about that.

741s are plenty strong. and i would trade my 742 open pig for a good 741 SG unit. under an early A with a mild v8 and relatively skinny tires...the 741 would last forever.........
 
Hey, no worries. Bottom line is that they are all plenty strong for a street car. Personally I think a tapered shaft might be stronger than one with a step machined in it, but I see your point on the larger thrust bearing and yes, the crush sleeve is a crappy design.
 
Something I found interesting,, is that further down the page on the 2 sites that Swing69 and Cazbah362 use for reference,, is a list the apps for the diff/axles..

64 Max Wedge 53-1/4" Parts Manuals list four different axles for this housing:
2070573 - 741 case w/o SG 30-1/2" overall;
2404003 - 742 case w/o SG 30-1/2" overall;
2070695 - 741 case SG 30-7/16" overall;
2404050 - 742 case SG 30-7/16" overall;

741 behind the Max Wedge..
 
RustyRatRod said:
The 741 is correct for the A body, but it does not matter. Any of them will work fine.
Click to expand...

Will the driveshaft, u-joint size, and axle spline all be the same? I'm looking to take my open 2.76 rear out, as it's not doing me any dragstrip favors....
 
The axle spline count (30 spline) is the same on all factory 8-3/4's. The driveshaft from your 7-1/4 will not work with the 8-3/4. Different length. There are a few different yokes. I believe all A-bodies used the small 7260 yoke. You could find the small yoke in some other body styles also but it's hit or miss.

Here's a good article comparing several different differential pinions

http://www.doctordiff.com/blog/tech-info/rearend-pinion-comparison/
 
fishy68 said:
The axle spline count (30 spline) is the same on all factory 8-3/4's. The driveshaft from your 7-1/4 will not work with the 8-3/4. Different length. There are a few different yokes. I believe all A-bodies used the small 7260 yoke. You could find the small yoke in some other body styles also but it's hit or miss.

Here's a good article comparing several different differential pinions

http://www.doctordiff.com/blog/tech-info/rearend-pinion-comparison/
Click to expand...

Thanks for the info! I already have an A-body 8 3/4 under it, I just need to change the centersection. I see posi's with gears (complete centersections) come up from time to time, and was just wondering if they are pretty much a bolt-in.
 
fishy68 said:
The axle spline count (30 spline) is the same on all factory 8-3/4's. The driveshaft from your 7-1/4 will not work with the 8-3/4. Different length. There are a few different yokes. I believe all A-bodies used the small 7260 yoke...
Click to expand...

My 68 383 Formula S came with large yokes.
 
JQmile said:
Thanks for the info! I already have an A-body 8 3/4 under it, I just need to change the centersection. I see posi's with gears (complete centersections) come up from time to time, and was just wondering if they are pretty much a bolt-in.
Click to expand...

The 3 different case numbers will bolt in your housing. You may run into different yoke sizes, but that can be fixed with a conversion u-joint or by swapping the yoke.
 
I bought a 68 Roadrunner 4 speed parts car some time ago, all HD underpinnings, 11" drum brakes all the way around! Spec'd for a 741 open case!!! Go figure!!
 
66fs said:
My 68 383 Formula S came with large yokes.
Click to expand...

Not sure what I was thinking earlier but I remember that now. In fact I believe the 69 440 Cuda had the large yokes also. I should have said I think all small block and /6 powered cars came with the small yoke. Although with ma Mopar you can rarely bank on anything, LOL
 
fishy68 said:
Not sure what I was thinking earlier but I remember that now. In fact I believe the 69 440 Cuda had the large yokes also. I should have said I think all small block and /6 powered cars came with the small yoke. Although with ma Mopar you can rarely bank on anything, LOL
Click to expand...

I can't imagine a HP big block without them, but you are right about Ma Mopar.
 
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