Project FD RX7 Restomod: Part 15 – Building the Ford 8.8 Differential with a Detroit Truetrac LSD and WPC

Ford Explorer Diff Housing RepairWe took our diff to Mario at TSR Fabrication, and he welded up the crack and machined down the inner surface to make it round again.

Ford Explorer rear cover modification for Ronin FD RX7 SwapWhile at TSR, we started to follow the directions from the Ronin Speedworks Explorer 8.8” swap kit, by cutting off the ears of the differential rear cover.

Cutting ears off Ford Explorer 8.8 rear cover for Ronin RX-7 swapAfter cutting off the ears, we had to cut the reinforcement ribs down at an angle for more clearance.

Mounting ears cut off Ford Explorer 8.8 rear cover for Ronin RX-7 swapOnce the reinforcement ribs were cut down, we cleaned them up a bit

2010 Ford Explorer 8.8 rear diff cover modified for Ronin FD RX-7 swapWe took a grinding wheel to finish the ribs with a bit of a CNC machined texture and look to it.

20 comments

  1. Looks like a win-win upgrade (adding a clutch-type LSD, reducing the assembly’s weight, and improving durability). Really enjoying this project – thanks for sharing all the progress!

  2. It’s always great to hear Mario’s named mentioned from TSR. He’s an artist with a welder. I love all the work he has done for the Datsun community.

  3. Awesome to see the attention to detail on the ring and pinion gears! All that work will increase the fatigue life by magnitudes.

  4. Love it. I’m still waiting to see a brake rotor WPC treated to see how much longer the brake distances would be.

  5. Whats the difference in length, axle centre to driveshaft flange between the two diffs? Currently have an aftermarket clutch type diff in the OEM housing that I don’t really trust behind a T56 Magnum. It’d be a shame to bin/remake the carbon driveshaft shaft…….they look pretty close!

    1. The Ford Explorer 8.8″ diff flange (using the Ronin mount) is 0.425″ rearward/closer to the axle centerline than stock. It sounds like your best bet is to get a 0.425″ spacer to adapt your driveshaft to the Ford 8.8 diff flange.

  6. Perfect – thanks Billy. That’s better than trying to go the other way! Looking forward to your next instalment.

  7. While the out side of the assembly might be larger, it’s no guarantee of greater strength. A measurement of the gears and the bearings would be needed to make that claim. The fact the Ford unit is lighter is also a factor. Also the original mounting with the PPF is quite strong, as the lever arm of the PPF is much longer than the bushings located right at the companion flange.

    1. Size does not determine strength, but the 8.8″ Ford gear and aluminum diff housing are known quantities to handle over 1,000hp. The FD’s PPF and cast iron diff housing are also known quantities and known to be weak and unreliable in the 400-450whp range.

  8. Hi there can sombody tell me which model Eaton Detroit Truetrac LSD was used please?
    Eaton Part number please?
    Many thanks

  9. What brand and weight gear oil is recommended for the Ford 8.8 differential? This would be for FD RX-7 Drift Car, thanks!

    1. It depends on what limited slip differential you are using. For the Eaton/Detroit TrueTrac, it is crucial to use a conventional, NON-synthetic gear oil with NO friction modifiers. Lucas Heavy Duty High Performance 80W-90 Gear Oil, and Torco RGO Racing Gear Oil 80W-90 are good options that fit these requirements.

    1. Motive Gear F888430 Ring & Pinion Set, Ford 8.8″ Standard, 4.30 Ratio, 30-Spline, 10-Bolt, 8620 Steel, Compatible with F-150, Mustang, Explorer, Crown Victoria, Ranger, Lincoln, Mercury (1980-2020)

      Then once the CD009 transmission was chosen, it was changed to:
      Ford Racing M420988355 8.8″ 3.55 Ring and Pinion

      1. We appreciate the build details, and for the reply. Starting to gather parts for our own build, thanks to you all.

  10. Did you stick with stock Ford Explorer front mount bushings? They seem to hold up fine since install?

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