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 8 3/4 Rear End

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Evil_Fury
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PostSubject: 8 3/4 Rear End   Sat Nov 19, 2011 4:58 am

8 ¾
The only Banjo axle produced by Chrysler.
Introduced 1957…DOA by 1974
Last year in A bodies: 1972
Last year in E bodies: 1974

This is "the” axle to run on the street. A plethora of gear ratio's exist OEM and aftermarket (except for 741), easy centre section swapping (run the economy centre section during the week and swap in the big gear centre for drag racing), great strength. It looks like a Ford 9" with the centre section being retained in the housing by a circle of nuts on studs in FRONT of the differential.

YEARS

1957 - 1964
This 8 ¾ has its brakes attached to the axle shaft by a large nut. I don't know anything about them but to avoid them. Casting # 1820657

1965 - 1974
This 8 ¾ has flanged axle shafts as used on later A bodies.
A body Info: 55.6" width (flange to flange) / 51.4" housing flange to flange / 43.02" spring seat centre to centre

8 3/4 CENTRE SECTIONS
The 8 ¾ came with several different centre sections as listed below some are stronger than others:
657 1957 - 1964
741 1965 - 1974
742 1957 - 1968
489 1969 - 1974
****NOTE all centre sections are interchangeable into any 8 ¾ housing. So if you have a weak 741 centre section in your A body 8 ¾ you can swap it for a 742 or 489 with no problems.


8 3/4 CASTING NUMBERS
1820657 AKA "657"
The 657 is as equally weak as the 741 described below but nowhere near as common. It is a 1 3/8" pinion shaft unit like the 741 and was discontinued in 1964. This was the year when Chrysler dropped the tapered axle shafts that had the brake assembly attached to the axle with a keyway and large nut. If you see this rear end....RUN! However, the pumpkin can be swapped into a later housing or rear end.

2070741 AKA "741" :
The 741 is the weakest 8 ¾ centre section you can buy. Commonly found in V8 A bodies before 1973. (Rumour: It is the only available axle in 1972 Darts / Valients….matter of fact is where I got my rear end from and it had a 741 in it but I swapped it for a 489 for $20.00 more)
The 741, besides being the weakest of the 8 ¾, has a limited amount of OEM and aftermarket bearings, gears, and other parts available. This unit when found in an A body rear is usually loaded with highway gears (However, I found a sure-grip 3.91 741 centre section in a 1967 cuda 340 "S" 4 speed car) and will have to be replaced with a stronger unit if you want to race. Best advice…try to swap it for a 742 or 489 section before you take that A body rear from the yard. If that is not possible it makes a nice cruising / backup unit.
A lot of people on the web boards hack on the 741 that it is too weak but most agree that it is hard to break it in a mild street application. So if you have a nice strong small block street car you will be hard pressed to bust this pumpkin. Sure grips found in these rears can be swapped into other housings as long as you take the carrier bearing and races with you (as they are different). SG's themselves are all the same except for the clutch and cone type units.
Info: 1 3/8 Pinion

2070742 AKA "742":
A real good section with lots of bearing/gears/parts available. Biggest gear ratio available 5.57. It doesn't use a crush sleeve like the later 489 so a lot of racers prefer it. If you find one with an original sure grip it is almost 99% odds in favour it is a sweet clutch type. More on this later.
Info: 1 ¾ Pinion

2881489 AKA "489":
The strongest of the 8 ¾ units. As with the 742 there are tons of replacement parts available as well as gear ratios. Gear ratios available beyond 3.23 are: 3.55, 3.91, 4.10, 4.30, 4.57, 4.86, 5.13 and 5.38. Almost all original sure grips, except 1969, found in this housing are the non rebuildable and less desirable cone type. Also with suregrips there is a bit of noise on the net as which are better. The clutch type are rebuildable and the best for racing. The cone type are not rebuildable but are perfectly acceptable for a street car. They last at least 40 - 50K with means many years of abuse with a weekend driver. If you need a SG for a car, can't find a clutch type to rebuild, are not a racer go buy a new one for $300 - 350. I would not buy a used cone SG though.
Info: 1 7/8 Pinion

NOTE: All cases, pinions, bearings, gears are not interchangeable between the three units but the sure grip units themselves are. There are two types of sure grips:

Dana Power Lok, 1962 - 1969 which are rebuildable (clutch packs)
Borg-Warner Spin Resistant, Late 1969 - 1974 which are not rebuildable (cone type)

An easy ticket to a cheap sure grip is to find a clutch unit in an orphan 741 case and remove it with the bearings (pressed on) and races and swap it into your better carrier (742 or 489). Most people don't think they are swappable so whine to the seller that it is a 741 SG and negotiate hard. Once the unit is out remove the old 741 ring gear, install yours from your better pumpkin, install a new clutch pack (rebuildable remember? Most are worn out after 30 years. Clutch kits are available from Mopar or Mancini and others) and then swap the whole mess it into your 742 or 489 case. The ring gear bolts are left hand threaded so remember this and don't break any as you may need them. Also if you go this route double check the gear mesh pattern to make sure it is set up ok.


Sure grips can be found in performance cars, trucks, vans, etc. so you have to look for them. There are two types of suregrips, cone and clutch. The clutch type, Dana "Power - Lok" came in the earlier 657, 741 and 742 carriers from 62 - 69 and is rebuildable. The MP rebuild kit for this type of SG is PN# P4529484 and it consists of new clutch disks and plates.
The later cone type suregrip commonly found in 489 carriers was produced by Auburn Gear before Borg Warner bought them out. It is called the Borg Warner "Spin - Resistant". It has a bunch of springs you can see looking in from the side of it.

Well, I need to clarify something concerning cone type SG's and their lack of being able to be rebuilt. They can be and there was an article in High Performance MOPAR Magazine, May 1997, PGS 28-30 where they did it. They removed 0.080" off each cone in a lathe and installed a 727 high clutch piston return spring (one each) into the center of each of the four original springs. The article is fairly easy to follow with good pictures.

Interesting note in the 1998 MP catalogue they show a picture of an open differential and under it they call it a Sure-Grip. Big mistake there. The PN# P4876118 is their SG replacement (cone type) and it lists for $625.00, whew! You can purchase a new SG from Mancini Racing for about $350.00 and it is the same thing as Auburn makes them all. If you decide to go this route you will need to purchase new carrier bearings and set the rear end up again.


OPEN (NON - SUREGRIP) DIFFERENTIAL
(NOTHING INSIDE)
POOR QUALITY JPEG IMAGE OF A TYPICAL CONE TYPE DIFFERENTIAL
(NOTICE THE SPRINGS)
SURE GRIP (CLUTCH TYPE "POWER LOK") DIFFERENTIAL
(THIS IS THE ONE TO BUY!)
SAME DIFFERENTIAL TAKEN APART
HERE ARE SOME PICS OF A 489 3.55 SURE GRIP (POSI) DIFFERENTIAL.
AS YOU CAN SEE ON THE CASTING NUMBERS IT'S A 489.. LOOK AT THE END OF THE TOP SET OF NUMBERS..489.
HERE'S ARE SOME PICS OF A 742
AND A PIC OF A 741
As you can see there is a great deal of difference in the drums when you compare the 1958 8 3/4 to the 1970-74 E-Body 8 3/4. WOW!! (Plus you don't need a drum puller to get the drums off the E-body rear.

I'll get some pics comparing the complete rears soon. The awesome thing is that the E body rear will bolt right onto your 1957-58 Plymouth..

1958 Drums
1970-74 E-Body Drums
Here's some info I found that I thought would be worth sharing.
Every once in a while someone is asking what diff out of what car and how long...




Originally created by Chrysler in 1957, the 8 3/4-inch rear was used in many Chrysler cars and Dodge trucks through about 1974. These differentials have a removable carrier, which, like the Ford 9-incher, unbolts from the front. It's also called a "banjo-type" differential assembly, because that's basically what it looks like from the center housing out to either axle.


Ten bolts retain the carrier, and the pinion spline can be either 10-spline or 29-spline. Obviously, the ring gear is 8.75 inches in diameter. Identification of these rear ends is pretty straightforward. There are only six identifying part numbers relating to a true 8 3/4-inch rear. Some of these you will probably never see, because they have not been in any applications after 1964, but they do turn up occasionally. The casting numbers are stamped into the center housing, on the driver's side.

Casting numbers 2070742 (used from 1961-1969) and 1634985 (used from 1957-1964) identify the 1 3/4-inch-diameter 10-spline pinion shaft, and are commonly referred to as the "742" case.

Casting numbers 2070741 (1964-1972) and 1820657 (1957-1964) identify the smaller 1 3/8th-inch-diameter, 10-spline pinion shaft, and are often called the "741" case.

Casting numbers 2881488 and 2881489 were used from 1969 through 1974 and were the only cases used after 1973. This is the most sought-after 8 3/4-inch version, and is called the "489" case. The pinion shaft diameter on these rear ends was 1 7/8 inches, and these pinion shafts were either 10- or 29-spline.

The increase in diameter of the pinion shaft also relates to the rear-end assembly's strength. Normally, the 741 cases were used in A-body or lighter cars with smaller engines. The 742 cases were normally for mid-sized models or higher-horsepower engines. The later model 489 cases would be used in heavier cars or higher-performance engines.

Ring and pinion ratios are primarily identified by a tag on one of the carrier mounting nuts, and the ratio followed by an "S" would indicate the Chrysler "posi"-style Sure-Grip assembly.

There is, in most cases, another tag identifying the limited-slip additive and the proper type gear oil that needs to be used in this assembly. This tag would also be attached to one of the 10 carrier nuts. Many ratios were available as options from Chrysler, but the more popular passenger-car ratios were:

2.76 (47-17)
2.94 (47-16)
3.23 (42-13)
3.55 (39-11)

Truck ratios were available as tall as 5.57. One of the advantages of using the 8 3/4-incher is that there are no carrier breaks, so the ring and pinion you do find can be changed to any ratio between 2.76 and 5.57 without buying an additional carrier. Another advantage is the fact that the non-limited-slip rear assemblies can be modified to a Sure-Grip limited-slip differential just by exchanging the carriers. The only year the Sure-Grip wasn't offered in the 8 3/4-inch configuration was 1957. In the earlier applications, from 1958 to 1969, a Dana limited-slip unit called a Power-Lok was used. This assembly incorporated clutches to give the differential its locking capabilities. From 1969 to 1974, Chrysler vehicles used a spring-loaded cone assembly called a Borg-Warner Spin-Resistant assembly to provide the locking ability of the differential.

Finding one of these rear-end assemblies shouldn't be difficult. Things to look for when sourcing this unit are the casting number, ratio, whether it's already a Sure-Grip, and whether it was made before or after 1964. The pre-1964 axles were tapered and held the brake assemblies in place by the use of a key and locknut. Later applications used flanged axles, with the ability to make slight adjustments in width by use of an adjustable axle retainer used on the passenger-side axle. The later-model axles are also not tapered, so it's possible to have them cut and re-splined to fit narrower-width applications.

Here's a list of cars and trucks you can look at to find one of these differentials:

1964-1976 Dart, Demon, Scamp, Duster, Barracuda, Valiant
1957-1974 full-size Newport, New Yorker, Imperial, Polara, Monaco, Fury, and 880
1962-1974 Satellite, Coronet, Charger, R/T, GTX, Belvedere, Road Runner and Super Bee
1970-1974 'Cuda and Challenger
1958-1974 D100 and W100 pickups
1964-1970 A100 vans
1971-1974 B100 and 200 series vans

There were several different rear-end housing widths used on these models. All measurements are from brake drum to brake drum:

1966-1972 A-bodies - 57 1/8th inches
1962-1963 B-bodies - 58 1/2 inches
1964-1967 B-bodies - 59 1/2 inches
1970-1971 Imperial - 59 3/4 inches
1968-1970 B-bodies - 60 1/8 inches
1970-1974 E-bodies - 61 5/8 inches
1965-1969 C-bodies and 1965-1970 A100 vans 61 3/4 inches
1965-1966 Imperial - 62 inches
1967-1969 Imperial - 62 5/16 inches
1970-1971 C-bodies and 1971-1974 B-bodies - 63 inches
1965-1971 D100 pickups - 64 inches
1969 C-body wagons and 1971-1973 B-body wagons - 64 3/8 inches
1970-1973 C-bodies and 1972-1974 D100 pickups - 64 3/8 inches

Spring-perch measurements between the two leaf-spring mounting pads can range from 43 inches to 47 1/2 inches. This means that the leaf spring perches to mount this differential into your car may have to be moved in or out on the axle tubes with the help of a good machine shop or welder, for correct fitment to your project.

As we said earlier, these rears are easily adaptable to numerous other manufacturers, as well. They are very popular with street rod builders as an alternative to the Ford 9-inch or the GM 12-bolt rears, because they are so easily modified to suit your performance needs.

For muscle or street machines, for instance, the 1971-1974 B-body 63-inch axle will fit quite nicely under 1970 to 1979 Ford Torino, Ranchero and 1972-1979 full-size and intermediate Fords, in addition to the 1967 Fairlane, and even 1935-1936 Plymouths.

The A-body axle, at 57 1/8 inches, is similar in length to the 1957 to 1959 Fords, the 1964 1/2 to 1966 Mustangs and the 1968 to 1970 AMC AMX, Gremlin, Hornet and Javelin. Earlier applications could include 1928-1940 Fords.

The early B-body units, at 59 1/2 inches, will fit under 1937 and 1948 Mopars, and the 1971 to 1974 Javelins and Rebels, too. Early B-body units will also adapt to 1939-1948 Chevys and 1941-1948 Fords.

E-body differentials from 1970 through 1974, measuring 61 5/8 inches, can be used in 1957 to 1972 Ford pickups and 1960 to 1964 Ford full-size cars.

The 1965 to 1969 Imperial rears, at 62 inches wide, can be adapted to 1955 to 1959 Chevy pickups or 1954-1956 Ford pickups. They could also be considered for 1970 to 1981 F-bodies and 1968 to 1972 A-body GM models as well, being only 1/-inch narrower than the stock GM differentials.

Should you find a non-limited-slip rear end, or one with a smaller ratio than desired, numerous drivetrain specialty suppliers and ring-and-pinion shops can sell you replacement gears. Gear ratios available range from 2.76 to 5.57, depending on the case number and the aftermarket ring and pinion supplier you use. Yukon, Richmond Gear and West Coast Differential all offer different combinations. Posi kits and locker assemblies can also be purchased to upgrade to the Sure-Grip differential. Borg-Warner sold the production rights to their Spin-Resistant unit to Auburn Gear Company quite a few years ago.

Dana Power-Lok clutch assemblies are still available through Mopar Performance outlets, as well. Adapter u-joints are also available to convert your existing driveshaft to fit the yoke on the Mopar 8 3/4-inch rear. Additionally, aftermarket suppliers sell new spring perches if they're needed for those cases in which the leaf springs don't match up and the perches have to be relocated.

Checking into pricing with some of our sources, we find that they range from $1,750 for a complete new assembly, including brakes, to around $1,000 for a reconditioned unit. Used Sure-Grip units from a salvage yard will probably run you in the $375-$500 range, but most of the units not yet bought up are from trucks, and thus too wide for most passenger-car applications.

Some recent classified ads for 489 cases have asked as much as $400 for just the Sure-Grip dropout carrier. But equipped with some of the information we have given you in this article, you should be able to visit a swap meet or a Mopar-friendly salvage yard, with your tape measure and micrometer in hand, and find a unit that will work for your particular project for less than $600.

Keep in mind that all 8 3/4-inchers aren't Sure-Grips, but if you find one that matches in terms of spring perch location and/or wheel track width, it can be cheaper in both time and effort to buy that assembly and upgrade it than to search for a 489 case with 4.11 gears already installed for your '72 Challenger. Used non-Sure-Grip rears are abundant, and sell for as little as $100 to $200.
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PostSubject: Re: 8 3/4 Rear End   Sat Nov 19, 2011 10:41 am

You know Chuck this is great information, but they are saying the 741 is weak but that is not so. I used to make sure I had the 742 or the 489 housing, but in my ol RedSled plymouth the 741 is the only one I have ever run in it, nainly that is what I can get for my price and those things with the posi's are going for 4-5oo dollars now. If I ever need to I have a 742 housingto build, but as lond as the 741 works for me I will keep it in there.

I am running 500 plus HP with 391 gears, could go lower and get a better et , with a 3500 stall and launching a 4000 lb car, I have turned a 1.78 60 ft No Problems.

What I am trying to say in most cases of our members cars a 741 would be plentyh heavy enough. Smile

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