sdolsay
Well-Known Member
There is a large 9 cast into the side of my carrier, does this mean it's a "489" rear and if so is this a good thing?
Thanks!
Thanks!
Yes Its A 489 Case And Its The Stongest Of The 3.sdolsay said:There is a large 9 cast into the side of my carrier, does this mean it's a "489" rear and if so is this a good thing?
Thanks!
Yes Its A 489 Case And Its The Stongest Of The 3. Is That Your 74 In The Pic. Is It Hemi Orange. I'm Doing A 72 In The Same Colour. Blackened Out Hood And Gowing.sdolsay said:There is a large 9 cast into the side of my carrier, does this mean it's a "489" rear and if so is this a good thing?
Thanks!
340mopar said:It is debatable that the 489 is not the strongest and that the 742 is. It still is a very good case though.Chuck
I build a bunch of Mopar thirds and I agree with everthing that GJ said. The 489 and the smallest of the three the 741 use the same front pinion bearing which is alot smaller than the 742. My case of choice is the 742. Not taking anything away from the 489, it's a plenty tough third also.Guitar Jones said:Not really much of a debate, the 489 is strong and will serve most any purpose well. However the 742 case has the biggest rear pinion bearing of any passenger car rearend ever. As such it can take the most load of any of the 8.75 cases. It's also the case Ma Mopar used when they commissioned the aluminum center section. It also uses shims for pinion preload from the factory instead of the crush collar (which is a weak point as it can lose it's tension) so you don't have to spend extra money for the aftermarket spacer. The only real difference is the pinion stem diameter. Since the 742 is larger than a Dana 60 (1.75 vs 1.626) I don't think there's a problem there.
Either way the 489 is a great case for high performance street and strip use. I still use a 742 aluminum case in my Scamp, which came out of my Duster. Which ran 10.60 at over 3000 pounds. Granted it's not a four speed (I broke every one of them) but I have used it for a season with a tranzbrake without ill effect.
657 and 741 are the same,Just like the 985 is the early model of the 742. They only made three different designs from 1957-1974.Johnny Dart said:I beg to differ with you guys.
There were four different 8 3/4" carriers which were used from 1957 through 1974.
The 1820657 carrier,which was used through 1964,and the 2070741 carrier,which replaced it,are both of the light-duty variety.The 2070742 carrier used a pinion with a 1 3/4" diameter,and was considered the heavy duty carrier until 1969,when it was replaced by the 2881489 carrier.The 2881489 carrier used a pinion with a tapered stem and was the heavy duty unit from 1969 on.The 489 carrier is the strongest of the lot......
ValiantMike said:Below is from Moparts Tech Archive
Strength Considerations
-----------------------
Pinions...
The 1-3/8" '741' pinion is the weakest. It is still a capable unit in most
moderate power, moderate traction street applications. For high torque
applications with high traction tires, the 1-3/4" or 1-7/8" should be
considered.
The 1-3/4" '742' has a larger rear pinion bearing yielding greater strength
in this area.