After some reading I do not think the typical Mutang/Ranger rear axles are wide enough for the Eagle. Are they? Has anybody measured them? If they are not wide enough, the Exploder 8.8 might be your best Ford choice. The factory late '80s Cherokee Dana 44 is still the best choice I'm aware of as it is almost 100% direct bolt-in.
To measure the additional fuel cost of an 8.8 over a 7.5 would be splitting hairs. I doubt one could accurately measure the difference in anyway other then in a lab with a dyno. Fuel pumps are notoriously inaccurate to the point that the extra fuel to drive an 8.8 would not be measurable. The only way I can think of to get a rough idea in the typical garage would be to measure the force needed to rotate the axle with a beam torque wrench. Even then the measurement would be in lb/in, not lb/ft. Car Craft did an article sometime within the past two years where they measured the (drag) difference between a GM 12-bolt, D60, and the Ford 9 inch using this method. The point was to see how much hp it took to drive the various and most common axles used for high hp cars. The big difference was not the weight of the components so much as the difference in pinion angle in comparison to the ring grear. The 7.5 and 8.8 are close enough that if setup properly should be very close in terms of the power needed to drive them. I predict one would have to do a lot, a LOT of driving for a long, long time to realize any difference in fuel expense between the two axles all else being equal (ratio, driving habits, car, engine, load, etc...).
In terms of on or off road driving, if you are going to go through the expense and labor of swapping to a different rear axle the 8.8 is still the smart choice over the 7.5 IMO. The 8.8 has a lot of aftermarket support where the 7.5 does not. Gears, bearings, brakes, weld-on brackets, axles, etc...all readily available for low cost. Other then a free or near free axle from a neighbor, the junkyard is full of the 8.8 axle so finding one for cheap is easy enough. If you are fortunate enough to have a pull-a-part-type salvage yard near by a rear axle will be cheap. Find a 1995 through 2001 Ford Exploder. Lastly, the additional strength is not just a little, but a LOT. All things being equal (cost, labor/time to complete the swap, parts, etc...) getting the extra strength is just smart. Even if you don't intend to go off-roading in time you might go to a taller or wider tire, pull a trailer, or load up the car and go camping for a week. Might as well have the extra strength, no reason not to.
Matching the front axle gear ratio is key. You'll have to look around and see what options are available for your factory front axle. Highest I could find for the 8.8 is a 3.08 gear. If you can find a front axle out of a four cylinder Eagle you can change to a deeper gear and possible find one that will match up with an 8.8 offering. There are a lot of variations in the Eagle front axles/housings, so I'm not going to go into that here. It is documented here on the AMC Eagle Nest. Finding a tall gear for the 8.8 is difficult as the Exploder is heavy and needs a deeper gear. Add in the aftermarket is supporting drag racing and off-road applications and they make them deeper, not steeper. Finding a matching gear ratio between an Eagle front axle and an 8.8 might be the only sticking point.
Personally I'm looking for the 4 cylinder Eagle front axle housing and the late '80s Cherokee rear d44. If you take the time to research and settle on a set of matching front axle and 8.8 rear axle gear ratios, please post up your findings.
Topic: Rear axle swap (Read 8393 times)