Ford 8.8 Axle Swap
After much research and debate I've decided I'm going to give my Dart a new rear axle, but due to the increasing scarcity of proper, vintage A-body MOPAR 8-1/4 and 8-3/4 axles I'm going to use a much more common and readily available Ford 8.8 axle from a Ford Explorer.
So why the Ford 8.8? There are many good reasons for this axle choice but one right off the top is that these axles are very, very common in junkyards right now (2018).
Why the Explorer as the donor vehicle? There are 4 reasons:
1 - You get a choice of drum or disc brakes depending on the year of the donor vehicle. Pre-95 Explorers have 10" (10x2.5) drum brakes, and 95 and newer vehicles have disc brakes.
2 - The Explorer axle is the stronger version with 31-spline axle shafts. Earlier versions and versions used in applications like some mustangs and rangers used weaker 28-spline axle shafts (though likely still adequate for a slant 6). The 31-spline shafts are larger in diameter and the axle tubes are larger in diameter.
3 - The axle is not symmetric/equal length, the driver's side axle tube is longer than the passenger side by 2-7/8 inches. If you cut the driver's side axle tube down by 2-7/8 inches, you can use two passenger side axle shafts and you have an equal length axle. Relocate some spring perches and it will mount into the '64 Dart on the stock 2-1/2in wide leaf springs.
4 - You can get limited slip diffs. It is very common to find Explorers with limited slip differentials. Look for a door tag axle code starting with a D (like D1, D2, D3, D4) or look for an 'L' on the metal axle tag (should be held on by one of the diff cover bolts). If the tag states # L ## (example 3 L 73) then the axle has a limited slip. My example axle would have a 3.73 gear ratio and a limited slip.
The axle I pulled came from a 1994 Explorer so it had the 10in drum brakes. For my Dart with a Slant 6, these will be plenty adequate. I also got very lucky and found a donor with a 3.27 gear ratio open differential (door code 41). The 3.27 ratio is not common on the Explorer (more common on Mustangs), the 3.73 seems to be the most common ratio. Of the five 1992-1994 Explorers I looked at in the Pick-n-Pull yard four of them had D4 axle codes (3.73 limited slip axles). I don't really need a limited slip, but a D1 axle code or 3 L 27 metal tag code would have worked for me as well. I wanted a 3.27 axle because my stock MOPAR 7-1/4 has 3.23 gears. By selecting a 3.27 axle it's close enough to my 3.23 gears that I don't need to worry about my speedometer gear.
I don't know if decoding the VIN will tell you what the factory axle ratio would be but the VIN of my donor vehicle was 1FMDU34X6RUC09341.
So why the Ford 8.8? There are many good reasons for this axle choice but one right off the top is that these axles are very, very common in junkyards right now (2018).
Why the Explorer as the donor vehicle? There are 4 reasons:
1 - You get a choice of drum or disc brakes depending on the year of the donor vehicle. Pre-95 Explorers have 10" (10x2.5) drum brakes, and 95 and newer vehicles have disc brakes.
2 - The Explorer axle is the stronger version with 31-spline axle shafts. Earlier versions and versions used in applications like some mustangs and rangers used weaker 28-spline axle shafts (though likely still adequate for a slant 6). The 31-spline shafts are larger in diameter and the axle tubes are larger in diameter.
3 - The axle is not symmetric/equal length, the driver's side axle tube is longer than the passenger side by 2-7/8 inches. If you cut the driver's side axle tube down by 2-7/8 inches, you can use two passenger side axle shafts and you have an equal length axle. Relocate some spring perches and it will mount into the '64 Dart on the stock 2-1/2in wide leaf springs.
4 - You can get limited slip diffs. It is very common to find Explorers with limited slip differentials. Look for a door tag axle code starting with a D (like D1, D2, D3, D4) or look for an 'L' on the metal axle tag (should be held on by one of the diff cover bolts). If the tag states # L ## (example 3 L 73) then the axle has a limited slip. My example axle would have a 3.73 gear ratio and a limited slip.
The axle I pulled came from a 1994 Explorer so it had the 10in drum brakes. For my Dart with a Slant 6, these will be plenty adequate. I also got very lucky and found a donor with a 3.27 gear ratio open differential (door code 41). The 3.27 ratio is not common on the Explorer (more common on Mustangs), the 3.73 seems to be the most common ratio. Of the five 1992-1994 Explorers I looked at in the Pick-n-Pull yard four of them had D4 axle codes (3.73 limited slip axles). I don't really need a limited slip, but a D1 axle code or 3 L 27 metal tag code would have worked for me as well. I wanted a 3.27 axle because my stock MOPAR 7-1/4 has 3.23 gears. By selecting a 3.27 axle it's close enough to my 3.23 gears that I don't need to worry about my speedometer gear.
I don't know if decoding the VIN will tell you what the factory axle ratio would be but the VIN of my donor vehicle was 1FMDU34X6RUC09341.
