Swap a Ford 9" axle in to your YJ
Swap a Ford 9" axle in to your YJ Short Cuts

By: Greg Colburn-03/2003

The weak 35c will be coming out soon enough, making way for the much stronger 9" unit.
It is hard to believe that this will be a functioning unit when we are done.
The third member housing and gears are in terrible shape and will have to be replaced.
This shows the cleaning and replacement that will be needed to make this a functioning unit.
Here is the housing, all cleaned up with all of the mounts removed. A heavy handed approach with the wire wheel was needed.
After the axle was cut down to size, it was necessary to weld on new Moser end caps.
The new Moser 31-spline axles have arrived. These are a heat treated alloy, handling 7,000 ft. lbs of torque per axle.

Wanting to switch the Jeep to 37" tires, I started to take a look at what upgrades will be needed to run that tire size with out instant breakage to the weak Dana 35C and Dana 30. After researching every option available for axles, I decided on swapping in a Ford 9" axle in the rear and a Dana 44 for the front, this article will cover the rear portion of the swap. There are several options available when going with this configuration. First you can go completely turn-key, and buy a unit from any of the available manufacturers that will ship to your door a complete unit with brakes, lockers and everything else you would need. The second option is to buy a used unit that has already been built privately and pick it up usually at a reduced cost from new. The third, and the one that I chose to go with, is to start from the bottom up. This maybe the longer road, but you will have the confidence that the axle you put under your vehicle will be the way YOU want and not the way someone else felt it should be.

I chose the Ford 9" for a few reasons: The 9" features larger non c-clip axles, much larger brakes (2.5"x11"), numerous locker options and a wide range of gear ratios to choose from. In addition to these features, the Ford 9" also has a removable third member which allows easy gear set-up and the option to swap in different third members if needed. The 9" also is stronger than a Dana 44 and gives you more ground clearance than the Dana 60. The Ford 9" however does have a lower pinion that will create a steeper drive shaft angle.

The first step is to locate an axle. After two months of endless nationwide searches through junk yards, bulletin boards and parts dealers an axle was finally located. The donor axle was found in a dumpster 5 miles from my house where my brother is employed. It was not the prettiest thing I have ever seen but it was free, and that was a great start

The axle was placed on jack stands where the taking apart process could begin. I started with the brake drums which needed to be sledge hammered off in pieces, and the axle-retaining bolts that needed a lot of elbow grease to be set free. Once the axles were removed, I removed the third member and brake lines, inspecting everything as it was removed. The real luck came when after everything was apart and inspected, I noticed that not only did I have the big brake/big bearing unit, it was also a 31 spline axle which we will come back to later. Now that you are only left with the housing it's time to start cleaning. Solvents and pressure washing is needed to clean the axle tubes and housing. Many people will sand blast the housing, leaving debris in the axle tubes that must be cleaned before installing new parts. Now that the housing is apart and somewhat clean, it was time to send it to Randy's Off-Road in Marysville, WA to begin the work

First on the list was to grind off all of the shock mounts and spring perches. Next, the housing was wire wheeled to removed scale and stubborn rust. Since I was not interested in installing a full width axle, it was time to measure for the housing surgery. The axle was cut down to the stock 60" WMS dimension and new Moser end caps were welded on to the tubes. Just when things were going smooth, the axle that came out of the unit was double tapered and unable to be machined down to fit the new housing length. To rectify the situation, a call was placed to Moser and two new 31-spline axles were ordered to fit and arrived within a couple of days. In addition to the new axles, new bearing cups, backing plate pins, Moser axle seals and bearings were installed.

On to the third member: The third member was in bad shape, so everything was replaced including the housing. Randy had a spare nodular housing lying around his shop so it was quickly commandeered to house the new 4.88 gear set. I plan on driving the Jeep to most of the trail runs and events and since it will see pavement, I opted to go with the ARB air locker that will allow me to engage it with a switch on the dash while not having to experience any of the on-road characteristics of non-selectable lockers. I called ARB in Seattle, and thanks to Visa my new locker and compressor arrived within a couple of days. Concurrently with the gear work, the new shock mounts and spring perches were tack-welded in place awaiting final placement and weld. After the gears were set up, and the ARB was installed it was placed back in to the housing.

Almost everything was replaced on the axle due to its dilapidated condition. After salvaging the numbers from the previous brake drums, new shoes, drums, cylinders, self-adjusters and hardware was ordered to fit the housing. Once the brakes were installed, it was time to place the housing under the Jeep and align all of the mounts and perches.

Set up on the axle was straight forward due to the fact that I was staying spring under in the rear for now. The new axle was placed underneath the Jeep and the bolt-in process began. Welding on new perches allowed the elimination of the degree shims, while setting the correct drive shaft angle. Once the shock mounts and perches were welded fully in to place, the new u-bolts were tightened, the drive shaft was connected and the brake lines were installed. There was some discussion if the stock emergency brake set-up would work with the 9", but it in-fact connected right on without any issues.

One thing you must keep in mind when performing this swap, new wheels will be needed because of the larger 5 on 5.5" bolt pattern versus the stock YJ 5 on 4.5", and if you are not modifying the front in any way it may be tricky to carry 2 spare tires to fit the different lug patterns.

With the wheels bolted on, and everything tight it was time for the test drive and ramp to make sure everything was working properly and there were no rubbing or clearance issues when articulating the suspension. Once on the ramp, it was discovered that the shocks were to short on the collapsed dimension, and new Skyjacker Nitro shocks were installed. The test drive was very un-eventful; this is not something that will add horsepower, or any noticeable difference to the on-road performance to the vehicle especially with the ARB differential. The real test will be on the trail when you are able to shift in to 4WD and not wonder if this is the time when the weak Dana 35C decides to implode.

arb2.jpg third.jpg testfit.jpg installed.jpg
The new ARB will be installed in the third member providing solid traction at the flick of a switch. The old housing was replaced with this stronger nodular housing with pinion support. It has been stuffed with 4.88 gears and an ARB Here is the axle under the Jeep for the test fitting. The new axle under the Jeep and ready for the trail.

  • Randy's OffRoad
    Dept. ORN
    14702 Smokey Point Blvd
    Marysville, WA 98271 USA
    Phone: (360) 659-5259
    Dept. ORN
    20 Spokane St.
    Seattle, WA 98206 USA
    Phone: (206) 264-1669

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