1981 Mazda RX-7 Rear Axle

Merry Christmas!

Hope everyone is having a happy holiday.

Now for the rear axle. As mentioned previously, it is good to replace the differential and axle seals if you are restoring the car. The axles are held in by three bolts that hold a plate to the axle, and slide out easily once the bolts are removed. The seals are inside the axle and pop out with a flat head screw driver easily. The differential should be inspected for damage and wear. This is what your axle looks like disassembled and partially cleaned up. When taking the differential apart, remember how it goes together. The order of parts from inside out is as follows: Crush tube (which shouldn't be tampered with unless replacing the ring and pinion), Conical pinion bearing, differential seal, mounting plate, washer, lock bolt (which should be new as well - can get this from racing beat along with your differential seal)


Take everything out of the axle, clean up the rust, wipe it down and put some fresh paint on it. It is good to put a rust-proof primer on the metal, two coats of a base-coat primer, three to four coats of a base coat and two to three coats of the clear. If you are using an enamel, life is much easier. Here is a picture of the primer being put on.


When reassembling the axle, the bolts get tricky. To attach the differential back in place, clean up the edge of the axle and differential where the two mate to ensure proper contact. Re-tap the holes on the axle: the bolts are Grade 8.8 M8x1.25 and should have a length of 20mm to ensure proper attachment. Place black rubber RTV sealant as the directions on the product describe around the inner and outer diameter of the differential hole on the axle, and tighten down the bolts. Allow at least a day for the sealant to cure. Slide in the axles (after lubed up) and use the same bolts but with nuts as mentioned before to attach the seal plates on the ends. The support arm needs reattached as well, using the same bolt thread. For the drain plugs however, you need to use Brass Pipe Fittings (not flare fittings or black iron pipe fittings) with 1/2 thread. Two of these will fit in the drain and fill holes. Next fill this baby with oil, slosh it around, drain that oil and refill it. This ensures that all debris during assembly has been removed. The parts list for this portion requires the use of:

16 -M8x1.25x20mm Grade 8.8 bolts
16 -M8 locking washers
6 -M8 Grade 8.8 nuts
1 -Extra long (length unknown) Grade 8.8 M8x1.25 series bolt (this goes through the differential, if you have the original, save it for reference)
2 -Brass Fittings 1/2 end caps
1- 1/8 threaded nipple (works as a place for a vent tube to be reattached - place RTV on the last few threads and by hand thread it into the top hole where the drain plug was inserted)
1-Tube of RTV sealant

Having a nice, smoothly operating and shiny rear axle for your restomod project is always nice. I suggest using Royal Purple Gear Oil for these applications: the additives work better in high performance applications, whether it be off-roading in 100 degree heat or running your Cobra at 6,750 rpm for hours.