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A-body 8¾ Inch Axles

by engineer CudaPete

The 8¾ or 8.75-inch axle was found in the A-bodies from 1968 to 1972. A similar model was available in the earlier A bodies, but it was a different axle, with tapered shafts that changed in 1966. It really became more common in 1968, so we’ll talk about that one.

8.75-inch Mopar axles for A-bodies (Dart, Duster, etc)

The A body was a Dodge Dart, Demon, and Swinger, Plymouth Valiant or Duster, and first-generation Plymouth Barracuda. The axle could be found other other cars and even trucks and vans, as it was used for heavy duty service; and it was paired with the 318, 340, 383, and 440. These would all be with the A-727 automatic or a manual transmission. Starting in 1970 it was only the 318 and the 340, and again it was with the 727 or manual—you could also find this as part of the towing package with the Slant 6 up front or for a heavy duty application. The 8¾ was never found before the 904—well, probably not. Things did happen.

Here’s the video.

This is called the Hotchkiss or banjo design, because the center section is removable with these bolts; you can take the whole center section out with the bolts, very similar to the Ford 9 inch. This is also known as the banjo type because some people think it looks like a banjo when this is removed.

Now, where do we get 8¾ or 8.75? That’s the diameter of the ring gear. This was in service up until in A bodies up until 1972; they are different from the ones in B bodies. From end to end, flange to flange, this is 52 5/8 inches wide and then spring perch to center is 43 inches. In the case of the B body, this is going to be wider by around a half inch on either side, because it’s a bigger car. There are some subset differences between the two, too. This particular housing is a 1970 to 72 variant—the vent for the axle tube is located on the driver’s side. Shorter, maybe 1/4 of the way down the axle, if this was 1968 or 69, the vent tube would be located more towards the center section, so it's a little different when you're looking at these designs.

The center section is the same regardless of the car body. There are three different variations of the center section. The first one is the 741; the numbers are cast into the side, and the 741 is the small type. It has a one and 3/8 inch stem pinion pinion here. The next one up would be the 742 case with a little bigger stem pinion, one and three quarter inches. Then the biggest one, the 489, has a one and seven eighth inch tapered stem pinion. These are cylindrical stem pinions whereas the 489 is a tapered design. The 741 is fine for most street applications. The 489 is considered the most robust, so it’s needed in truly high-force applications.

Many gear ratios were available since this could be found in trailer towing packages, trucks, vans, cars. They've got 2.76, 2.93, 3.23, 3.73, 3.90, and 4.10:1.

These are also available with the SureGrip, which is Chrysler's word for Posi-Traction. There were two types of SureGrips. The earlier version is the clutch type, the later one is the cone type. One way you can tell whether an axle has SureGrip is by turning the axle; if both sides go in the same direction, it’s a SureGrip. If they go in opposite directions, it’s an open rear rim. So this one is a 3:23 with a cone type SureGrip.

There are two types of U joints. There's the small one, the 7260, and the large one, 7290.

The driveshaft is also unique for these axles, because a lot of cars came with the 7¼ axle, whose housing is 2¼ inches shorter than the 8¾. That means the drive shaft has to be two and a quarter inches shorter in the big axle. You should still measure it, but you’ll have to shorten the driveshaft by two and a quarter inches if you move to the bigger axle. They're the same length on both sides and all A body eight and three quarter inch rear ends are small bolt pattern, meaning 5 on 4 lug nut configuration with right hand threads on the passenger side or right side. They have left-handed lug nuts threads on the drive’r side or left side of the car.

These never did come from the factory with the big wheel bolt pattern, and they never did come with the right-handed lug nuts on the driver side, so they're all small wheel bolt pattern and they are all configured right hand thread/left hand thread. You can use stock bearings which are a tapered roller bearing; but you can put in a sealed bearing, most commonly known as the green bearing. The big benefit with that is there’s no end play adjustment as with the tapered bearings. You have to have an end play adjustment on one side, not a big deal to do, but with the sealed bearings you just put them in. Tighten it down and you’re good to go.

There are some differences on these cars depending on years, like I was saying. If you're going to do that conversion for the seven and a quarter, these have 3 inch axle tubes, a small wheel bolt pattern seven and a quarter has 2 1/2 inch.

A lot of specialized parts on this rear axle are unique to A-bodies. That transfers down to the brakes. There are three sets of lines available and three different tee because of the different applications. The 1968-69 brake tee looks the same from the top, but is rounded off on bottom to match the profile of the housing in its original location. In 1970 they moved it to avoid rounding the bottom and in 1972 it has a completely diffrent block seat and brake lines. You have to be careful with that.

There’s also a different brake hose for the connection to the to the main brake line where the 1968-69 is approximately 1 inch longer than the 1970 or 71, so you have to make sure that you get the right correct rubber brake hose to connect the system up.

This was just a general overview of what is involved with these axles for the A bodies from 1968 to 1972. There's a lot of questions out there about what parts fit which years, what interchanges, what doesn't interchange. A lot of people try to modify bigger housings from the B body or C body to make them nowhere to fit within the A body confines, but if you can find one of these, it’s usually best if you can get what's correct for the car.

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