school me on 8 3/4

[mopower440]

Please forgive my ignorance as i am just now getting back into this. Many years ago i built my Dart and had a lot of knowledge stored in my head. Lost interest for quite a while and am now back to messing with my dart again and changing some things. So, i have an A-body 8 3/4 rear end in the car. Has the 741 case with 3.23 clutch style sure grip. Has the original small bolt pattern axles still. I am going to swap out the center section with a different gear ratio. Now, i cant remember if any of them will work with my axles or if there was different axle spline counts..?

 

[1WildRT]

741/742/489 all interchange... If the new unit is a clutch style make sure it has the thrust buttons..

 

[33IMP]

ALL 8 3/4s have 30 splines, so your axles will work. (except for aftermarket 35 spline spools, that require 35 spline axles).
Just curious. Which way are you going with ratio? What case #? V

 

[Vaanth]

Please forgive my ignorance as i am just now getting back into this. Many years ago i built my Dart and had a lot of knowledge stored in my head. Lost interest for quite a while and am now back to messing with my dart again and changing some things. So, i have an A-body 8 3/4 rear end in the car. Has the 741 case with 3.23 clutch style sure grip. Has the original small bolt pattern axles still. I am going to swap out the center section with a different gear ratio. Now, i cant remember if any of them will work with my axles or if there was different axle spline counts..?

Stock center sections, or others with the stock axle spline count of 30, will interchange.

The following guide may be helpful. It is dated, but still useful:

A Chrysler 8-3/4"Rear Axle Guide

 

[1MeanA]

Last time I looked at 741 gear selection it wasn't great.
Mopar 8 3/4" (8.75) Ring and Pinion for 741, 742, or 489 case

 

[65 Dartman]

Last time I looked at 741 gear selection it wasn't great.

IIRC ratios available were 2.76, 2.94, 3.23 and possibly 3.55 for the 741. Dr Diff built me a 741 2.94 SG for use in my 47 Dodge

 

[4mulas]

741/742/489 all interchange... If the new unit is a clutch style make sure it has the thrust buttons..
View attachment 1716490982

Only if he’s using tapered bearings? Otherwise not really required. Yes he said stock a-body axles but maybe someone has changed to greenies.

 

[1WildRT]

Only if he’s using tapered bearings? Otherwise not really required

IMO it's the only bearing to use..

 

[4mulas]

Y

IMO it's the only bearing to use..

es. Much stronger and not that hard to set up. Don’t know why people don’t use them as much any more. Cost?

 

[33IMP]

Y

es. Much stronger and not that hard to set up. Don’t know why people don’t use them as much any more. Cost?

Simpler. You don't have to worry about having the right plug in the suregrip, or having the exactly correct length axles. WAY simpler if the housing is narrowed.

 

[33IMP]

Dr Diff built me a 741

IIRC ratios available were 2.76, 2.94, 3.23 and possibly 3.55 for the 741. Dr Diff built me a 741 2.94 SG for use in my 47 Dodge

I'm guessing all of those 3.23 and higher gears were oem Mopar, and not available new anymore. Last time I looked for a 741 gearset, all that was available was 3.55, 3.73, and 3.91. and I'm not sure about the 3.91.

 

[1WildRT]

Simpler. You don't have to worry about having the right plug in the suregrip, or having the exactly correct length axles. WAY simpler if the housing is narrowed.

And yet somehow through the years I've narrowed over a dozen axles & got it right every time.... A little more challenging, sure, but worth the effort IMO..

 

[mopower440]

ALL 8 3/4s have 30 splines, so your axles will work. (except for aftermarket 35 spline spools, that require 35 spline axles).
Just curious. Which way are you going with ratio? What case #? V

Not sure yet as i am looking for one..I want a 3.91 gear, not too picky about the case #

 

[mopower440]

Thanks everyone, i appreciate it! So when i first bought this 741 with 3.23 that i am currently using, it was originally an open diff. I bought the clutch style sure grip unit and installed it in the center to make it positive traction. If im remembering correctly it was pretty easy. Let me ask, if i were to find a 742 or 489 center section that is open, can i install the clutch sure grip from my 741 case into it or will it not work because the case number is different?

 

[Vaanth]

Thanks everyone, i appreciate it! So when i first bought this 741 with 3.23 that i am currently using, it was originally an open diff. I bought the clutch style sure grip unit and installed it in the center to make it positive traction. If im remembering correctly it was pretty easy. Let me ask, if i were to find a 742 or 489 center section that is open, can i install the clutch sure grip from my 741 case into it or will it not work because the case number is different?

The Sure Grip, and also the open type, carrier can be interchanged between the differential housings if the matching differential bearings are retained. The side bearing cups themselves differ, and the inner cone differs, but the outside diameter of the cups are the same between the '741'/'742' and the '489'.

Bearing Timken numbers:
- '489' Differential, side LM 104949/LM 104912
- '741'/'742' Differential, side 25590/25520

 

[1WildRT]

Pardon Our Interruption...

 

[mopower440]

The Sure Grip, and also the open type, carrier can be interchanged between the differential housings if the matching differential axle bearings are retained. The side bearing cups themselves differ, and the inner cone differs, but the outside diameter of the cups are the same between the '741'/'742' and the '489'.

Bearing Timken numbers:
- '489' Differential, side LM 104949/LM 104912
- '741'/'742' Differential, side 25590/25520

so if i were to install the sure grip unit itself from my 741 unit into, say a 489 open diff center to make it positive traction, i would have to buy the outer axle bearings (wheel bearings) to install on my axles that would have been on the axles used in the 489 case? am i understanding this correctly? Im guessing there is not enough adjustment on the passenger side axle bearing adjustment? Or could i just use the green axle bearings for any of the 3 different carriers?

 

[mopower440]

Pardon Our Interruption...

I saw that, but im assuming i have the 10 spline pinion yolk from the literature that vaanth posted above and this 3.73 set has a 29 spline pinion...BUT, is it possible to find a 29 spline yolk that takes the same size u-joint i am using?

 

[33IMP]

I think he's referring to the carrier bearings, not the axle bearings (I think he misspoke)
Google the bearing numbers, I think you'll find they are carrier bearings.

But I could be wrong. Do some research.

 

[33IMP]

I saw that, but im assuming i have the 10 spline pinion yolk from the literature that vaanth posted above and this 3.73 set has a 29 spline pinion...BUT, is it possible to find a 29 spline yolk that takes the same size u-joint i am using?

Yes
There are basically four passenger car yokes. Fine spline, big and small joint, and coarse spline, big and small joint.

 

[mopower440]

Yes
There are basically four passenger car yokes. Fine spline, big and small joint, and coarse spline, big and small joint.

This is what i currently have, not sure if it is the big or small joint..I forgot so much about this through the years. Thats what i get for losing interest for so long..and im getting old.

 

[1WildRT]

Far as I'm aware all 741 gear sets use the 10 spline yoke... As does the 742... Only the 489 uses both

 

[1WildRT]

Yours is the bigger joint 7290...

 

[33IMP]

Far as I'm aware all 741 gear sets use the 10 spline yoke... As does the 742... Only the 489 uses both

The aftermarket 741 3.73 set you posted uses a fine spline. (#16).

 

[mopower440]

Yours is the bigger joint 7290...

Thank you!! So i can find a fine spline yolk with the 7290 size so i can use the 3.73 gear set that has the 29 splines, correct? Nothing else would be different about the yoke that
would be a problem? Like this one..
Pardon Our Interruption...