Differential case number on a 8-3/4

[1969CoronetR/T]

I am changing out my rear gears from 4.10 to 3.55:1. I want to rebuild my sure grip unit but do not know the case. Can someone tell me where the seven digit case number is on a 8-3/4 rear end? Strange Engineering and Moser both advised staying away from a Detroit locker and Auburn posi units.

 

[lewtot184]

the number is on the side of the housing. usually parallel to the pinion.

 

[1969CoronetR/T]

It is at a transmission shop up in the air with the drive shaft out. The 4.10's are great for red light acceleration, but I have to watch my engine as the RPM's are close to 4000 doing 55 MPH.

 

[super-bee_ski]

The numbers should be one of these 3:

741: 1-3/8" small stem pinion (aka. '741')>
Carrier casting numbers: 1820657 (1957-1964), 2070741 (1964-1972). This assembly was typically used in low weight/low horsepower applications through low weight/medium horsepower and high weight/low horsepower applications. Pinion depth and bearing preload is set with shims. Differential bearing setting (ie. backlash ) is set with threaded adjusters. MAX WEDGE cars had this carrier.


742:1-3/4" large stem pinion (aka. '742')
Carrier casting numbers: 1634985 (1957-1964), 2070742 (~1961-1969). This assembly was replaced by a phase-in of the 1-7/8" pinion starting in the 1969 model year. 1970 RW (Plymouth and Dodge mid-size) were the last models to use the 1-3/4" which appeared in a 2881489 case. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Pinion depth and bearing preload is set with shims. Differential bearing setting (ie. backlash ) is set with threaded adjusters.



489: 1-7/8" tapered stem pinion (aka. '489')
Carrier casting numbers: 2881488, 2881489 (1969-1974). This assembly was introduced in 1969 and was phased-in to replace the 1-3/4" 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. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Pinion depth is set with shims, preload is set with a crush sleeve. Differential bearing setting (ie. backlash ) is set with threaded adjusters.

 

[Propwash]

 

[1969CoronetR/T]

I did not realize the number would be that large.

 

[Propwash]

I did not realize the number would be that large.

LOL! No doubt...

They don't get much larger, besides cast #'s on an engine block. To give you some credit, they're usually buried under a 1/4" of grease, dirt and road slime from leaky pinion seals.

 

[1969CoronetR/T]

Well I have the dreaded 741 case. I am thinking of getting a Moser 849 case with a Eaton Truetrac with 3.55 gears.

- - - Updated - - -

 

[1969CoronetR/T]

I ordered a 849 case, Eaton Truetrac, 1350 u-joint and 3.55 gears from Mosier Enginneering and it should be here first week of March to install that week. I will be selling this 2070741 case along with the 4.10 gears and the Sure Grip differential. I am not sure if the Sure Grip is the clutch or the cone type yet. Any ideas of the value of these used parts where the condition is good as it has worked fine for me the last five years?

 

[patrick66]

I've yet to break a 741 rear pumpkin, and I've run nearly 500 hp through one.

 

[1969CoronetR/T]

It ran fine with 400 HP but I now have 600 HP (or more) and I always hated the 4.10:1 gears in it. I upgraded my engine, transmission and now the rear end. Disk brakes are on deck for later in the spring / Summer after I see the effectiveness of my drums in stopping the R/T. I would imagine my R/T did not come with the 741 case.

 

[Propwash]

I ordered a 849 case, Eaton Truetrac, 1350 u-joint and 3.55 gears from Mosier Enginneering and it should be here first week of March to install that week. I will be selling this 2070741 case along with the 4.10 gears and the Sure Grip differential. I am not sure if the Sure Grip is the clutch or the cone type yet. Any ideas of the value of these used parts where the condition is good as it has worked fine for me the last five years?

Sounds pretty Beefy! 489 case should work good for you. Did you order an install kit? A 489 has a crush sleeve in the front, just wondering if the install kit has the crush sleeve or it's converted to the spacers.

 

[1969CoronetR/T]

I will have to wait and see when it arrives. Would a 69 R/T come from the factory with a 741 case?

 

[Propwash]

I wouldn't think so 1969coronetR/T, I believe the 741 was used for the lower HP models, but I'm not half the parts historian as some guys around here. I'm sure someone will correct me if i'm wrong.

 

[Matts68bird]

my 68 roadrunner has a 741 in it. does anyone know if this was standard for that years. I know it has been played with. my rear end spider is probably welded... I've read that there were a couple RR survivors with this casting case. just curious!

 

[Fran Blacker]

Think it should be 742 on driver's or 489 not sure what year they changed.