741 742 489

Hello

Anyone one know what the differeance is in these 8 3/4 center sections? I want to put one in a dodge pick up 2 wd 1/2 ton

Tech Archive...start here:
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R.

Let me be the first to say you need a Dana 60!

The Chrysler 8-3/4" rear axle assembly was introduced in 1957. It is a banjo-type, the differential is contained in a removable carrier assembly. The axle has an 8-3/4" diameter ring gear. There are three basic types available distinguished by their drive pinion stem diameter. The 8-3/4" axle was the primary axle assembly used in most car lines through 1972.

8-3/4" Axle Center Section Types

The 8-3/4" axle was available in three basic types. The types are differentiated by the pinion stem diameter....1-3/8", 1-3/4", 1-7/8". The choice of axle pinion assembly was determined based on the application.

1-3/8" small stem pinion (741) Carrier casting numbers: 1820657 (1957-1964), 2070741 (1964-1972). These numbers are found on the left side of the carrier assembly.

This assembly was typically used in low weight/low horsepower (Small Block as an example) applications through low weight/medium horsepower and high weight / low horsepower applications. Pinion depth and bearing preload is set with shims. Differential bearing setting (i.e. backlash ) is set with threaded adjusters.

1-3/4" large stem pinion. (742) Carrier casting numbers: 1634985 (1957-1964), 2070742 (1961-1969). This assembly was replaced by a 1-7/8" pinion starting in the 1969 model year. 1970 Plymouth and Dodge b Bodies 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 (i.e. backlash ) is set with threaded adjusters.

1-7/8" tapered stem pinion. (489) Carrier casting numbers: 2881488, 2881489 (1969-1974).

This assembly was introduced in 1969 and gradually replace the 1-3/4" unit through 1970 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 through high weight/high horsepower applications. Pinion depth is set with shims, preload is set with a crush sleeve. Differential bearing setting (backlash) is set with threaded adjusters.

All 8-3/4" carrier assemblies can be identified externally by the casting numbers. Additionally, the 741 commonly has a large X cast on the left side, the 742 may have a large 2 cast on the left side, and the 489 has a large 9 cast on the left side. Through 1965, the factory ratio was stamped on the identification boss, followed by an S if

Sure Grip equipped. After 1965, a tag was affixed under one of the carrier mounting nuts to identify the ratio. If Sure Grip equipped, an additional Sure Grip lube tag was sometimes affixed; later years sometimes had the filler plug painted orange.

Gear ratios available on the 8-3/4" axle through the years include:

2.76, 2.93, 3.23, 3.31, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17, 5.57.

what are your plans hp wise with the truck?

Probably wouldn't hurt any of them and they ALL have a downside.

I would Keep It Simple Sam and search for a 742 (preferred) or 741 sure grip which would from the factory both have the highly desired clutch type sure grip in the ratio you desire for your app. if the pinion yoke does not match your driveshaft there is a combo ujoint to easily solve that minor dilemma. EDIT there is also a 6.20 742 gearset (I have one)

i believe there was a 5.12 and a 5.38 gearset as well. i have two 5.38 setups on the shelf at present.

I destroyed a 5.67 that was purchased from Petty many moons ago... Several years back (20?)I know a 5.57 could still be bought for a 742...

The 741 and 489 cases both use the smaller front pinion bearing, the 742 use a larger front pinion bearing and race and they are the ones I prefer to use on any Mopar that will be beat on heavily and drove aggressively

They all physically interchange but the yoke has three different u-joint profiles and the pre-'64 center thrust block might not work with '66 and later rear ends.

Blazin' Bob, I need to remind you that 741 production carried over into the '70s and they came with the cone type Suregrip.

I also need to remind you that it has been 40+ years since the last 8 3/4 rolled off the production line. In that time any differential may have been tinkered with. For a while it was easier to get an Auburn cone type than the Powr Lock. You never know until you open it up.

Also, you make it sound like every 741 or 742 rear had a Suregrip factory stock. I'm sure you know that this isn't true, far from it.

You are more likely to find a Suregrip under a pickup or station wagon that someone used for towing, and in the high performance cars.

To the OP: The rear end only has to stand what the tires can resist. 741s outnumber 742s and 489s by probably 5:1. I have used a 741 in my '64Dog D100 and have made several long pulls with 6000 lb of trailer behind me. I have had no problems except for seals getting old.

IMHO the best and smartest thing you could do is telephone DoctorDiff. If you buy a limited slip, get it from him as well.

R.

I ran a 741 case 3.91:1 in the 12-second charger for years till the limited-slip started making noise, so even the "weakest" 8-3/4 is still pretty good in my book. 742's seem to be harder to find. The 489 with a crush sleeve eliminator kit might be strongest?
There are two different U-Joint yoke sizes, but also two different pinion spline counts making 4 different possible yokes. I think the 10-spline large U-joint yokes are really expensive compared to the other three, but I haven't looked into it in years. I went with a Strange S60 with spool when the Limited slip started making bad noises.

I did not know that. I stand correct(ed)

Open rear end only, the 64 and older thrust block is 1.25", 65 and newer thrust block is 1.5" so they will not interchange.

JohnRR on here will recommend a cone type sure grip as being the best..

742 with 4.56 gears and a sure grip is what I run in my 91 half ton short bed dodge truck with a 300hp crate 360 magnum.
Haven't had any issues with it at all.

what I would do is find/buy a good 742 sure grip in the ratio you want & you're set. it would have the desired clutch type from the factory & highly likely that has not been swapped (if you see no springs in there you are golden). I highly prefer a ring gear felpro gasket as opposed to using RTV. some heavy parts house gear oil (I forget the weight) with a bottle of furd sure grip additive. set your axle end play to .010

Thanks for your replies, I finally found a 742 case sure 3:23 for the cuda.👍