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Mopar Rear End Gear Set-Up Specifications

CHRYSLER

Axle type Pinion Bearing Preload New Inch # Pinion bearing preload used inch #

Ring Gear

back lash

Ring Gear

Bolts to case

Ft Lbs

Bearing side caps Ft Lbs
Chrysler 7.25 12-14 6-7 .006-.010 55 50
Chrysler 8" 12-15 6-8 .006-.010 55 60
Chrysler8.25 12-15 6-8 .006-.010 55 90
Chrysler 8.75 41 13-15 6-8 .006-.010 55 90
Chrysler 8.75 42 15-25 7-10 .006-.010 55 90
Chrysler 8.75 49 14-19 6-9 .006-.010 55 90
Chrysler 9.25 14-19 6-9 .006-.010 65 75
DANA 60, 61 and 70 17-30 8-10 .006-.010 100 80
 
 
REAR DIFFERENTIALS contributed by Sean Krasan, Austin, TX

Mopar has produced two types of rear axles in their history, Banjo and Carrier Tube.
Banjo axles have one-piece housing and a removable center section that contains the ring and pinion. This center section is bolted into the housing like a Ford 9" rear. This axle is the one and only 8 ¾ unit.
Carrier Tube axles have a center section which is an integral part of the unit with the axle tubes pressed or welded into it. Examples of this are the 7 ¼, 8 ¼, 9 ¼, 9 ¾ (Dana 60).

 


 
 

(Source: 1984 Direct Connection Chassis Book)

7 ¼
Junk…read no more. Introduced in 1960; it was a low performance axle for /6 and small V8 cars. Before you swap this unit out put some slicks on your car..rev up the engine good and launch real hard a few dozen times. Or street race your car for a night or two, or objective here is to blow it up.
The rear end will eventually go KABOOM. Lots of fun for all….bring a tow strap so you can get home. Casting numbers # 2070051, 3507881, 3723675
Info: 1 3/8" Pinion stem, 9 bolt cover, 55.6" width (flange to flange) / 53.2" housing flange to flange / 43.02" spring seat center to center.
SPECIAL NOTE: The 7 ¼ housing axle tubes are smaller in diameter than other units so the u-bolts and spring plates are useless if converting to a larger axle (i.e. 7 1/4 to 8 1/4, 8 3/4 or bigger).

8 ¼
Introduced in 1969. This rear end will be found in all Darts / Valients from 73 - 76 and also can be found in 340 Dusters and other A bodies. There is a sure -grip available beginning in 1973. This axle while not a real high performance piece is certainly good enough for a mild street car. So if you go for a disk brake swap and are pulling out those spindles etc. out of your 73-76 donor car just grab the rear and you will have a nice 4.5" wheel pattern all around and way better brakes to boot. Sure-grip units are commonly found in Diplomat cop cars throughout the 80's but that rear end is a bit harder to install than the 73 -76 due to the strange leaf spring mounting pads. These pads can be cut off the axle and replaced with more conventional ones if you wish. If your short on cash and you can't afford to get a 8 ¾ or find the time to locate the long 8 ¾ axles for re-splining the 8 1/4 is a real nice alternative for a while and CHEAP in the yards ($50.00 non sure-grip and $125.00 sure-grip here in Texas). You may never blow up the 8 1/4 with a mild small block street car.
Castings: 2852905, 3723598, 3723599
Info: 1 5/8 pinion, 57.6" wide, 10 bolt cover, 55.6" width (flange to flange) / 51.4 housing flange to flange / 43.02 spring seat center to center.

9 ¼
Introduced in 1973. It was designed to replace the expensive to produce 8 ¾ and by 1975 it replaced it totally for heavy-duty applications. Not offered in A - bodies.
Castings: 3507890, 3507891, 3723199
Info: 12-bolt cover.

9 ¾ AKA Dana 60
Introduced in 1966. This rear end was not offered in A body cars except for the Hemi. The early rear ends were 23 tooth "Power Lok" (1966 - 1969) differentials. In 1970 the 9 ¾ went to 35 tooth axle shafts and were called "Track Lok" differentials. These particular ones will interchange with 8 ¾ axles, bearings and seals.
Info: 10-bolt cover

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 center section "pig" swapping (run the economy gear "pig" during the week and swap in the big gear "pig" for drag racing racing), great strength. It looks like a Ford 9" with the pig being retained in the housing by a circle of nuts on studs in FRONT of the differential.

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 center to center

8 3/4 CENTER SECTIONS
The 8 ¾ came with several different center sections as listed below some are stronger than others:
657 1957 - 1964
741 1965 - 1974
742 1957 - 1968
489 1969 - 1974
****NOTE all center sections are interchangeable into any 8 ¾ housing. So if you have a weak 741 center 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 center section you can buy. Commonly found in V8 A bodies before 1973. (Rumor: 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 pig 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 favor 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.