Farley`s Dodge Diplomat Forum

Forum Index => The Library => Topic started by: Reggie on January 02, 2008, 16:38:43

Title: Rear Axles: Chrysler 8 3/4" Rear Axle & Swap Information
Post by: Reggie on January 02, 2008, 16:38:43
Chrysler 8 3/4" Rear Axle & Swap Information

Chrysler Corporation's 8.75" rear axle assembly first appeared in 1957.  The measurement refers to the 8-3/4" diameter ring gear. This gear, which is turned by the pinion gear, changes the direction of the power being transmitted to it. The pinion gear is turned by the driveshaft. It is a banjo-type (Hotchkiss) axle.  The term "banjo" means that the differential is contained in a removable carrier (or center section) assembly. When the carrier is removed, the empty housing resembles a banjo. The carrier is removed from the front of the housing, and is retained by 10 nuts on studs in the housing.  The rear of the housing is smooth with a non-removable rear cover that is welded onto the main housing. The housing and axle tubes are made from stamped and welded steel.

The 8-3/4" axle was the primary axle assembly used in most non-compact car lines through 1972.  It was also used in some high performance compact cars.  Of the many axle types that Chrysler used since 1960, it was also the only axle assembly developed by Chrysler. It was phased out because it was more expensive to manufacture than using the outsourced Spicer 7.25", 8.25" and 9.25" units.

There are three basic types of 8.75" carriers available, which are distinguished by their drive pinion stem diameter. The choice of axle pinion assembly was determined based on a combination of vehicle horsepower and weight. Below are the 8.75" axle carrier types.

8.75" Axle Carrier Types and Years of Production

Carrier Identification:
All 8-3/4" carrier assemblies can be identified externally by the casting numbers.  The casting numbers are cast onto an ID pad on the driver's side of the carrier just behind the 'snout' of the case where the yoke attaches to the pinion. In addition to the casting numbers:

Gear Ratio and Sure-Grip Identification:
Through 1965, the factory ratio was stamped on the identification boss, followed by an 'S' if it had a Sure Grip.  After 1965, a tag was affixed under one of the carrier mounting nuts to identify the ratio.  If it had a Sure Grip, an additional Sure Grip lube tag was sometimes added.  Later year versions sometimes had the filler plug painted orange.

Gear Selection:
Because of its popularity, a wide range of gear selections is available for the 8.75" unit.  Gear ratios available on the 8-3/4" axle through the years include, but are not limited to: 2.76, 2.93, 3.23, 3.31, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17 and 5.57. 

Interchange Notes:
Any complete 8.75" carrier will interchange with another 8.75" carrier in any 8.75" housing. The Sure-Grip assemblies also interchange.  However, none of the other separate parts such as cases, pinions and bearings will interchange.

Swapping an 8.75" Unit Into an M-body

There Are Three Ways To Do The Swap:

Best 8.75" Donors:

The 1965 to 1970 B-body 8 3/4" rear axle is the closest fit to the F/J/M platform because the spring perch centers are 44" compared to F/J/M bodies 44.46".  Although 1962-1964 units will also fit, they should be avoided because the brake drums are pressed on, requiring a hub-puller to remove them. 

B-Body models to look for are:
For swap reference:

Procedure with stock Iso-Clamps - Courtesy of Mark Mullins

The B-body rear has much smaller locator holes in the spring perches than the iso-clamp setup, so Mark and his dad used a hole saw to enlarge the holes to fit the M-body springs. He used the extra two holes in each B-body perch to temporarily bolt steel plates to them, so he could properly locate the pilot holes for the hole saw. The perches still rested entirely on the springs, since the springs were 2 1/2" wide, and the difference between perch centers for the two housings was less than 1/4" on each side.

Mark is running a 4.10 geared, Sure-Grip 8.75" rear in his 360 equipped 1987 Fifth Avenue. Other goodies are Eddie heads, 9.5:1 forged Speedpro pistons, a Comp Cams XE 274 cam, Hooker headers, exhaust cutouts, an Edelbrock RPM Performer intake, a 670 CFM Holley Street Avenger carburetor, and an A500 4-speed automatic transmission with a 2500 stall converter, deep pan and a TFOD shift kit.  Can you say "nasty"?


Links to 8.75" swap information on other F/J/M sites:

Title: Rear Axles: Chrysler 8 3/4" Rear Axle & Swap Information - Page 2
Post by: Reggie on January 24, 2009, 20:20:16
Chrysler 8 3/4" Rear Axle & Swap Information

Below are photos originally posted by Farley's member S-Type (https://www.dippy.org/forum2/index.php?action=pm;sa=send;u=10) showing how he reduced the rear spring offset by modifying the rear spring hangers.  The reduced rear spring offset relocated the axle locating pin centers to match up to B-body dimensions of 44" rather than the factory 44.46". 

Photos courtesy of S-Type (https://www.dippy.org/forum2/index.php?action=pm;sa=send;u=10)