Rear Differential ID

[Shakey]

1969 Charger R/T 440 Auto 8 3/4 w/ 3.23 ratio

My parts book says:

Mopar 8 3/4 Axel
Pinion Shaft Diamter
1 3/8 - 1820657 / 2070741

It states that either one of these numbers would be located 2" below the yoke. 

As you can see from the pic, my number is close - 2070742.

Does anyone know where this could have come from?  Newer or older car?

What do the stampings underneath the number mean?

[Just 6T9 CHGR]

Mike, the solid 1 3/4" pinion "742" case generally was found in 1968 and older cars.

For 1969 & later, the larger 1 7/8" tapered pinion, "489" case was used.

The small 1 3/8" dia. pinion "741" case was used in most lo-po applications up until '72......a Charger R/T would have not come with this rear.   You are reading the book wrong.

Originally the 742 case would have come with the rebuildable clutch type Sure-Grip (good thing)
The 489 case came with the non-rebuildable cone type Sure-Grip (not good)

The Sure-Grips are transferable between all 3 cases so you have to take out the center section to see what you actually have.......

The 742 case you have is the more desireable unit because of its solid straight pinion and clutch type Sure-Grip (if it hasn't been changed out already).  The 489 case has one weakpoint...the tapered pinion that uses a crush collar to get the proper preload.  Some say that this is a weak link because if the pinion nut loosens up .....well you know....

To be absolutely "correct" for '69 you would need a "489" case like I have in mine.......

Personally, I'd leave it alone

[Shakey]

Mike, the solid 1 3/4" pinion "742" case generally was found in 1968 and older cars.

For 1969 & later, the larger 1 7/8" tapered pinion, "489" case was used.

The small 1 3/8" dia. pinion "741" case was used in most lo-po applications up until '72......a Charger R/T would have not come with this rear.   You are reading the book wrong.

Originally the 742 case would have come with the rebuildable clutch type Sure-Grip (good thing)
The 489 case came with the non-rebuildable cone type Sure-Grip (not good)

The Sure-Grips are transferable between all 3 cases so you have to take out the center section to see what you actually have.......

The 742 case you have is the more desireable unit because of its solid straight pinion and clutch type Sure-Grip (if it hasn't been changed out already).  The 489 case has one weakpoint...the tapered pinion that uses a crush collar to get the proper preload.  Some say that this is a weak link because if the pinion nut loosens up .....well you know....

To be absolutely "correct" for '69 you would need a "489" case like I have in mine.......

Personally, I'd leave it alone

Well Chris, I finally have had some time to look over my parts book again since your reply.  For starters, thanks for the lesson on Mopar rear differentials however I still want to learn more.

As we know, my carrier has part number 2070 742 embossed 2 inches below the yoke. 

Is it safe to assume that my carrier is from a '68 or older car?  Would the 742 carrier have come in an R/T or a Hi-Po car?

If everything is the same since it left the factory, nothing being changed, then I will have the 1 3/4" solid straight pinion shaft and clutch type Sure-Grip guts inside - correct? 

This can only be confirmed by measuring it, which I will do next time I make my way to the farm and I am ready to switch things over to the new housing I intend to get in the next week or so.

How does one tell the difference between a rebuildable clutch type Sure-Grip and a non-rebuildable cone type Sure-Grip? 

Do you happen to have a photo of yours internally or another you had used for reference?

I imagine it would be quite obvious to look at but at this point in my education, I would not know the difference if I tripped over the two of them.

I am guessing that since my 2070 742 part number is not mentioned in the notes (see below) from the '69 parts book on Text Page 3-1:

NOTE: Two types of differentials are being used in production for 8 3/4" diameter gear axles.  With 1 3/8" diameter pinion shaft, the carrier has part number 1820 657 or 2070 741 embossed 2 inches below the yoke.  With 1 3/4" and 1 7/8" diameter pinion shaft, the carrier has part number 2881 488 or 2881 489 embossed 2 inches below the yoke.

These notes do not pertain to my carrier - correct?

As you know, I am all for putting the car back to the way it was when it left the factory but at the same time I have to be realistic.  If I have the more desireable carrier, lucky me!  I will take your advice and keep what I have, I just want to make sure I know what I have.

Thanks again for sharing your knowledge.

[Ghoste]

If you have the 742 case, then the 1 3/4 pinion is the only one which will go into the case, so you can rest on that.  The Sure grip unit could have been swapped but it's unlikely.  If it's a cone type, you will see a series of springs inside the differential unit itself.  If it's the clutch type, you will have am oval slotted window in the side of the case instead of a rectangular one (on the cone type) and you won't see springs but if you look inside, you may be able to see a clutch pack somewhat similar to the clutch pack in an automatic transmission.

[Just 6T9 CHGR]

From the moparts tech archive

http://www.moparts.com/Tech/Archive/axle/13.html

[Shakey]

From the moparts tech archive

http://www.moparts.com/Tech/Archive/axle/13.html

Very informative.  Lots of questions answered there.  Thanks.