Rear Axle Swap

Rear Axle Conversion : Standard Rotation D44 to Standard Rotation Ford 9"

As I mentioned in the front axle swap story, I hadn't originally planned on changing my rear axle. I was quite happy with my swapped-in TJ D44. It was a combination of several factors that eventually convinced me that a 9" axle would be a good choice as a rear axle for my TJ.

Why not keep my rear D44?

Front Dana 30, rear Dana 44

The TJ D44 I swapped in to replace my stock TJ D35C is perfectly adequate for my TJ's needs. I don't plan on running larger than 36" tires, so strength wasn't really an issue (although some would argue that a Dana 44 can't handle this size of tire). The only problems I had with the rear axle were the flimsy factory axle brackets. Had I decided to stay with the D44, I would have chosen to eliminate the factory brackets and replace them with the much beefier Rubicon Express brackets. Speaking of which, the front axle swap introduced a few extra factors: the front axle came with 5 on 5.5" bolt pattern, which was more practical for me since most of the vehicles I 'wheel with also run that same size pattern (i.e. common spare tires). This meant I would have to change the rear D44 from its stock 5 on 4.5" bolt pattern. Unfortunately, the wheel flange isn't large enough to have the 5 on 5.5" pattern drilled into it, meaning I would have to buy custom axle shafts. In addition, I would have to have the front full-size axle shortened (likely only on the long passenger-side) to match the width of my D44. Not a huge expense, but less than desirable since I wouldn't be able to use stock axle shafts for the front axle. F-150 front D44 axle shafts are very abundant and cheap, so it would be ideal to have that supply available. I could assemble axle shafts from a combination of F-150 D44 short shafts and EB D44 long shafts, but that would siphon away from Chris Waterman's source of spare parts.

Why a Ford 9"?

Rear 9", with new RE brackets.

Well, let's address why not first. My only serious concern was the lower and longer differential "snout" of the 9" compared to the D44. This would result in a worse driveline angle in the back where most of the problems arise for lifted CJs, YJs and TJs. Chris Waterman had swapped in a 9" as his rear axle in his YJ but he also gained alot of rear driveshaft length by installing a short V8 motor. Still, Chris' project did mean that a 9" was a possibility. If push came to shove, I would still have the option of getting a Currie 9" high-pinion 3rd member, but that would be quite expensive and limit me to the ring and pinion size of a Ford 8.8".

So, why "yes?" Well, one big factor which made my decision easier was when Rob Bryce helped me find a Ford 9" with the strong housing (it tapers/flares out along the axle tubes more than normal) and it had 31-spline axle shafts. 9" axles commonly have 28-spline shafts, so while I have a smaller source of spares, I have significantly stronger axle shafts that everyone assures me I will be unable to break with my 6 cylinder engine.

As a bonus, the 9" was the same width as my front D44. It turned out that both axles came out of mid- to late-70s Ford F-150s, which also meant that the 9" was also set up with the 5 on 5.5" bolt pattern. The difference in width from the stock D44 was a mere 4" (65" vs 61" flange to flange). Jeep gets away with such a wide stock axle by having extremely heavy backspacing on their wheels. I decided to run full-size axles to save myself the expense of shortening both axles (which would also require custom axle shafts for the rear axle). Wider axles would also provide more side-hill stability. It remains yet to be seen if the wide-track/short wheelbase will make my vehicle more likely to spin out slippery roads. With neutral offset of my current wheels, my TJ, post axle swap, is now about 4" wider on each side.

Whether or not I chose the 9" or the D44, I had decided that I wanted disc brakes for the rear to replace the stock drum brakes. I'd suffered long enough with poor braking with my larger-than-stock tires, and this axle swap offered me the opportunity to acquire larger disc brakes for both the front and rear. This was the 'custom' portion of the rear axle project, since no full-size trucks have come with four wheel disc brakes. For the stock D44, I had been looking at discs from the Grand Cherokee (ZJ). For the 9", more options were open to me as quite a few cars run 9" axles, notably Lincolns and Grand Marquis.

In retrospect, by having been able to avoid the expense of custom axle shafts as well as having to shorten the housings, I'm fairly certain my choice of the 9" cost approximately the same were I to have chosen to keep the stock D44 rear axle.

Modifying the Axle Housing

As you would expect, it was much easier to modify the rear axle housing than the front. The photos' captions should explain the process quite clearly.

Axle Brackets

Setting rear axle pinion angle.	RE brackets modified for larger diameter 9" housing.	Brackets temporarily tacked into place.
Welding coil spring perches.	Coil spring perch welds.	Coil spring and spring retainer.
Welding lower control arm brackets.	Checking angle measurements.	Tacking upper control arm brackets in place.
Aligning upper control arm brackets.	Aligning upper control arm brackets.	Aligning upper control arm brackets.
Aligning upper control arm brackets.	Upper control arm bracket on center housing, spacer for other side.	Upper control arm bracket weld.
Torched mods to rear trackbar bracket.	Rear trackbar bracket ground to shape.	Trackbar bracket welds.
Upper control arm and trackbar bracket welds.

Shock Absorber Brackets

Axle test mounted to measure clearances/angles for shocks.	Shock brackets tacked in place.	Shock test fit in shock bracket.
Shock bracket welds.