8 3/4 question

-
S

sdolsay

Well-Known Member
Joined
Jul 25, 2006
Messages
118
Reaction score
0
Location
Moorhead, Mn
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?

nine.jpg


Thanks!
 
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?

nine.jpg


Thanks!
Click to expand...
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.
 
It is debatable that the 489 is not the strongest and that the 742 is. It still is a very good case though.


Chuck
 
Moparwedden,

Yep, thats my Duster, I'm gonna do the same, add the dual scoops also, thanks for the info guys.

Gonna look around for a suregrip for it, do you think 3.55's will work for a mild 318? on rebuild I'm gonna use a comp cams extreme 268H I think, prob with #302 heads and eddy performer intake/carb.

I'm just looking to make it a fun street car :)
 
A sure-grip out of any of the units will work 741, 742 or 489 they are all interchangable as far as fitting from one case to the other. It is only the ring and pinion that is specific to the cases.

Chuck
 
yep, I just have no idea what the ratio of this rear is :), I don't want to tear it apart atm to look :)
 
If it is a non-suregrip just jack up one side and spin the wheel two full revolutions while counting how many times the pinion yoke turns. This will be your ratio, you have to spin the wheel two times because of the spider gear ratio.

Chuck
 
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
Click to expand...

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.
 
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.
Click to expand...
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.
 
Thanks for the info guy's, well since I only plan on this being a fun street car for now it'll be a mild 318/auto and later a mild 340/4-speed neither going over 375 hp it should work out just fine :)
 
I agree with you guys that the 742 is the strongest, I was just trying to let the guy down easy. 742's are all I use I sold my last 3.91 489 about six months ago.


Chuck
 
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......
 
You said it all-tapered stem-or necked down,and then theres the bearing.
 
The small bearing diameter is the same with all three and this is were the pinion would break if it did.

The inner bearing is largest on the 742 so it will carry more load.

Also why would MP make the aluminum center section out of the 742 style casting if it wasn't the strongest?

The tapered pinion was invented for ease of manufacturing... it is easier and faster to set pinion bearing pre-load with a crush sleeve instead of shims.


Chuck
 
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 1-7/8" '489' is supposedly the strongest. Although the stem tapers down

along it's length, it appears inherently stronger from a pinion stem

perspective and the inherent strength of the fine splines (OEM gears).

The 1-3/4" '742' has a larger rear pinion bearing yielding greater strength

in this area. The 1-3/4" shares yoke mount diameter and mounting nut

with the 1-3/8".
 
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......
Click to expand...
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.
 
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.
Click to expand...

See as I said this is where the load is applied, at the rear bearing. The stem diameter is a moot point as the Dana 60 has a smaller diameter pinion stem but yet it's a stronger unbreakable rearend.
 
You must log in or register to reply here.
-

Back
Top