8 3/4 question. I need a little help.

[charger chris]

What is the differences between 489 ,471,742 case in the 8 3/4?

[garner7555]

I copied and pasted this below off another website.     


''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.

[charger chris]

So the 742 case is the better( stronger ) one out of the 3. Thank you for the info.

[ACUDANUT]

Randy's ring and pinion claim the 489 case is the best. ?

[charger chris]

 

[cdr]

if you are worried about how strong an 8 3/4 is ,  GET a DANA 60   all the 8 3/4 are about the same strength.

[c00nhunterjoe]

Had the "WEAK" 741 case in my belvedere. Only broke axles in it. Blew the guts out of the 489 in the charger so put a 742 in i had, broke several sets of hardened axles in it so built a dana...... no more problems.

[John_Kunkel]

Randy's ring and pinion claim the 489 case is the best. ?

Kinda depends on what criterion you use for "best". Some think the larger diameter stem on the 489 makes it best but the smaller rear pinion bearing on the 489 makes it "less better" than the large bearing on the 742.

[ws23rt]

Randy's ring and pinion claim the 489 case is the best. ?

Kinda depends on what criterion you use for "best". Some think the larger diameter stem on the 489 makes it best but the smaller rear pinion bearing on the 489 makes it "less better" than the large bearing on the 742.

This is interesting information.   I always wondered how much practical difference their was between the two?

When these things fail just where is the most common place they break?

[garner7555]

if you are worried about how strong an 8 3/4 is ,  GET a DANA 60   all the 8 3/4 are about the same strength.

I agree.     The only real disadvantage to the 60 is weight, but that's where part of it's strength comes in.   

[charger chris]

Thank you for all the good info

[c00nhunterjoe]

Randy's ring and pinion claim the 489 case is the best. ?

Kinda depends on what criterion you use for "best". Some think the larger diameter stem on the 489 makes it best but the smaller rear pinion bearing on the 489 makes it "less better" than the large bearing on the 742.

This is interesting information.   I always wondered how much practical difference their was between the two?

When these things fail just where is the most common place they break?

Axles....

[c00nhunterjoe]

if you are worried about how strong an 8 3/4 is ,  GET a DANA 60   all the 8 3/4 are about the same strength.

I agree.     The only real disadvantage to the 60 is weight, but that's where part of it's strength comes in.   

If you start to nit pick the weight difference, there are plenty of other areas of a 2 ton charger to shave weight. But if you are that crucial to shave weight off the dana, you CAN make it weigh less then the 8 3/4. Mine is nearly identical in weight and i know people that have danas under the stock weight of the 8 3/4, just depeends on how much money you want to spend to do it....

[garner7555]

if you are worried about how strong an 8 3/4 is ,  GET a DANA 60   all the 8 3/4 are about the same strength.

I agree.     The only real disadvantage to the 60 is weight, but that's where part of it's strength comes in.   

If you start to nit pick the weight difference, there are plenty of other areas of a 2 ton charger to shave weight. But if you are that crucial to shave weight off the dana, you CAN make it weigh less then the 8 3/4. Mine is nearly identical in weight and i know people that have danas under the stock weight of the 8 3/4, just depeends on how much money you want to spend to do it....

That tends to always be the bottom line, how much money are you willing to spend?

[c00nhunterjoe]

if you are worried about how strong an 8 3/4 is ,  GET a DANA 60   all the 8 3/4 are about the same strength.

I agree.     The only real disadvantage to the 60 is weight, but that's where part of it's strength comes in.   

If you start to nit pick the weight difference, there are plenty of other areas of a 2 ton charger to shave weight. But if you are that crucial to shave weight off the dana, you CAN make it weigh less then the 8 3/4. Mine is nearly identical in weight and i know people that have danas under the stock weight of the 8 3/4, just depeends on how much money you want to spend to do it....

That tends to always be the bottom line, how much money are you willing to spend?

[John_Kunkel]

When these things fail just where is the most common place they break?

The hypoid pinion gear acts like a screw when torque is applied, it tries to screw itself out the front of the housing and, at the same time, tries to push the ring gear out the left side of the housing. This is where the 742's larger rear pinion bearing has the advantage, it resists side deflection which eventually results in gear tooth failure due to reduced contact area. Also, as the pinion tries to screw out the front it forces the ring gear out the back which often results in failure of the left carrier bearing cap. And then there's the spider gears in the differential...........

Surprisingly, regardless of the pinion stem size, they all step down to a smaller diameter at the front bearing which would seem to be a weak spot but they rarely break there (but they sometimes do).

[ws23rt]

When these things fail just where is the most common place they break?

The hypoid pinion gear acts like a screw when torque is applied, it tries to screw itself out the front of the housing and, at the same time, tries to push the ring gear out the left side of the housing. This is where the 742's larger rear pinion bearing has the advantage, it resists side deflection which eventually results in gear tooth failure due to reduced contact area. Also, as the pinion tries to screw out the front it forces the ring gear out the back which often results in failure of the left carrier bearing cap. And then there's the spider gears in the differential...........

Surprisingly, regardless of the pinion stem size, they all step down to a smaller diameter at the front bearing which would seem to be a weak spot but they rarely break there (but they sometimes do).

  You speak my language.   So in real life their is little reason to stress about having a 742 vs a 489.--This feels like mythbuster stuff.

I remember this being so important to so many over the years and never heard a lick about why.

[c00nhunterjoe]

On a street car that will probably never hook, any of the 3 pumpkins will be fine. 742 and 489 have more options for gears though. If you plan on abusing it and run sticky tires, consider spending the money on a dana. Thats my