Differential Axle Seal Replacement for 1999+ Miata

by Chris Eberle
West Point, NY

This differs from the procedure for the earlier Miata in that the entire axle must come out of the car to do this job. The axles don’t unbolt from a stub axle, the assembly is all one unit held together by the CV boots. Also, this procedure differs somewhat from the method in the factory shop manual. I discovered after an expensive mistake that you don’t have to separate the axle from the wheel hub.

Tools needed:

Parts needed:

Begin by jacking up the rear of the car and supporting it with jackstands. Remove the rear wheel. Unbolt the caliper and hang it from the upper A-arm so there isn’t any stress on the brake line. Remove the rotor. Remove the long bolt holding the hub assembly to the lower A-arm. Remove the axle from the differential. Most articles and the shop manual say to pry the axle out. I couldn’t do this because there just isn’t enough of a gap between the CV joint and the differential housing to get a prybar tip in. Plus, you risk damaging the soft aluminum on the housing. Instead, put the prybar tip against the CV joint and tap the free end with a hammer. The axle came out almost instantly this way and it’s a lot safer. Remove the bolt holding the hub to the upper A-arm. The axle and hub are now free of the car. Ease the axle the rest of the way out of the differential and set the whole mess on a clean tarp or cloth. Use a little gear oil to lube up the axle end and set it aside. Back on the differential: clean all the dirt and gear oil away with a rag. Take care that nothing gets in the differential. Pry out the old seal with a screwdriver. Be very careful not to scratch the seal bore. The seal is really in there so take your time. Once you have the old seal out, cut away all the soft parts so you can use it to install the new seal. Also, make sure you get the little round spring out. Sometimes, it stays behind in the differential. Clean the seal bore thoroughly with a rag. Lube up the new seal with lithium grease inside and out. To install it, press it in evenly with your fingers as far as you can. Keep it nice and straight. Then, using the old seal and a block of wood, tap the new seal all the way into the bore. The seal will go below the surface of the differential housing, that’s why you need the old seal. Make sure it’s completely seated and even when you’re done.

To reassemble: carefully guide the axle with the circlip gap up into the differential. Slide it in until resistance is felt. Have your helper push straight in on the hub to seat the axle in the differential. It will click into place. Make sure you can’t pull it back out easily. Reinstall the bolts holding the hub assembly to the A-arms. The upper bolt gets torqued to 40-56 lbs/ft. The lower bolt gets 47-54 lbs/ft. Make sure you reinstall the bolts in the same direction as they came out (nuts to the rear). It is best to torque these down with the wheels loaded if possible. Reinstall the rotor and caliper (37-50 lbs/ft). Bolt up the wheel and you’re done! You should check for leaks for the first few drives to be sure you seated the seal correctly. Also, check your differential fluid level before you clean up. Just pull the fill plug and squirt some fluid in there until it drips out, then you know it’s full.

A bit of advice for those who want or need to separate the axle and the hub: The shop manual says to reinstall the old axle nut flush with the axle tip and tap with a copper hammer to drive the axle out. I don’t know about you but I’ve never seen a copper hammer. I couldn’t find one in my area anyway. I don’t advise tapping on the axle with anything except maybe a hammer and a block of wood. I think the best way to do this job would be with a hub puller. The axle is an extremely tight a precise fit inside the hub. It doesn’t just slide in and out even with liberal amounts of grease. Hitting on the nut may damage the threads on the axle. I know because that’s what happened to me. I followed the directions and trashed the threads anyway. When I reinstalled the axle nut, I wasn’t able to get in on all the way. Unfortunately, I didn’t discover this until I had driven about 200 miles and the wheel bearing failed (the max play is .5mm, mine was about 5mm!) I bought a used axle and hub assembly (only $250 from Mazmart, lucky!). Even the new parts were hard to assemble. I had to use the axle nut to pull the axle into the hub until it was tight. The axle nut torque is 174-235 lbs/ft! You can only achieve this with the wheel on and the car on the ground. Just pop out the center cap to get a 32mm socket on the axle nut. Don’t forget to stake the nut when you’re done. It just takes a few taps with a hammer and punch to dimple the nut flange into the little notch on the axle. The manual says .5mm or more. Good luck! As usual, all caveats and disclaimers apply. If you aren’t confident doing this, take to the shop.

Back to the Garage

27 October, 2002