Rear Spotters Guide

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

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.

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 webboards 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. 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.


EASY…….If It doesn't have bolts in the rear of the axle but has nuts on a bunch of studs on the front you have an 8 ¾. However is it a 741 or better? There is no easy way to tell except to pick the car up or go under and look at the casting numbers. Sure grip/no sure -grip? Well just turn the axle shaft forward and look at the other side. If its turning the reverse way (backwards) its not a sure grip if it does turn the same direction it probably is one. There should also be ratio and sure-grip (if equipped) tags on the center section studs but they can break off. In addition there is usually a sure-grip "use sure-grip lube" tag on one of the axle wheel stud (if equipped). If the car has a worn out sure grip it may not check out like one so you still may want to open it for inspection. Also racers install spools and weld spider gears in open style rears so if that rear end seems like it is a SG open it up to make sure. BUYER BEWARE!

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 catalog 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.








All photos courtesy of Brianwo (except for the lousy cone SG JPEG) who hangs out on Toms' Moparts web board. He is one of the more knowledgeable people I have come across. Thank You Brian!

4.5" AXLE SHAFT 8 ¾
All 8 ¾ axle shaft A body rears are the arguably totally useless 4" x 5 pattern. To run a more modern and common wheel bolt pattern (4.5") you will need to do 3 different things:

1) Drill out the 8 ¾ axle shafts to the larger size. This can be done except the diameter of the locating "ring" on the axle is smaller than on the 4.5" rim pattern. If the wheel mounting holes in the rim elongate and then the wheel will not be centered on the axle causing all sorts of problems.
2) Cut Moser a check for $295.00 for a pair of their 4.5" A body axles.
3) Find an 8 ¾ B or C body station wagon (and others) 4.5" axles and have them shorten/resplined by Moser for $85.00.

I would like to refer to MODCUDAS site for axle donor data as they got it from a Mopar Action magazine article with a few of my thoughts thrown in. Axle length stated by them is at least 28" from spline taper to the bearings. I called Moser and after a little discussion it seems that Modcuda is right however what we are looking for is an axle that is a total length of 35+ inches (outside flange to the very end of the axle shaft).
I acquired my axles from a 1973 Fury III police cruiser. The "72 or 73 or any B or C body wagon" listed in Modcudas site is confusing. The C body Fury's had either the 9 ¼ or 9 ¾ in them while the smaller (?) Fury III had an 8 ¾. After looking around the yard I can understand the axle sizes. It seems that Chrysler was phasing out their 8 ¾ in 72 - 74 so they dumped them in them in slightly lighter duty WIDE WIDTH vehicles such as station wagons and vans so they needed longer axles. The heavier duty 9 ¼ , 9 ¾ are in the big boat Fury's and Newport's along with other vehicles. The Fury III donor car had a 400 engine in it.
Since the Fury III was a police cruiser it had the fat 11" drums with the widest 2.5" brake shoes (some are 2" wide) offered on a C body. This is a bit overkill for an A body and the additional mass will slow down you racers out there. If you plan to run such big drums you will need a proportioning valve to lessen the effect of them or you may get killed when you rear end locks up and comes around on you during a rain storm. Also going to a 4.5" axle bolt pattern will not allow you to use the 4" drums off the donor A body if you wanted them as they will no longer fit. You must take the larger drums/backing plates/etc. from your 4.5" donor car instead. I also grabbed the emergency brake cables but I didn't need them in the end as my original 7 ¼'s fit perfectly.
On Moparts discussion board, somebody was rebuilding an 8¾ axle and needed bearings and seals. Instead of paying the $90 bucks or so Mopar wants for each axle set he got them at Autozone for $16.99 (P.N. "Set 7" Timken match) each and the outer seals for $4.39 (P.N. 8704S) each. I cannot validate this but I thought it was interesting. Most bearings I have bought at Autozone were the "Timken" brand so check it out and be careful. Other Mopar part numbers you may need when you're rebuilding your 8 ¾ rear are the following:
Vent Tube P.N.# 4032798
Backing plate foam end seal gasket P.N.# 2070933
Steel backing plate shims P.N.# 2881314
Brake hose: P.N.# 3880999 ($$$$ Factory Rip off, buy aftermarket, i.e. Raybestos for half price).

I keep hearing that B body 8 ¾ rear ends fit into A bodies except that they are a little wider. I have never seen this swap but I wanted to provide the B Body 8 ¾ dimensions verses the stock A body 8 ¾ setup. The first measurement is the center to center spring pad width of the housing, the second is the total axle width flange to flange.

67 - 72 A body 43.02" 55.60"
62 - 70 B body 44.00" 59.20"
71 - 74 B body 47.30" 62.00"
71 - 74 B body Station Wagen 47.3" 63.4"