In the previous Failure Points segment, I discussed a recent front wheel bearing failure on the Super Touring 6 Miata. This failure was abrupt, and there was no indication of issues before the session. And as promised, here are the steps to replace the front wheel bearings on the Miata. A surprisingly simple process.
Choosing a Replacement
Front wheel bearings are a known failure point for Miata’s, particularly on racecars. Replacements come in two forms. First, the front bearing can be purchased separately and pressed into the old hub. Or buy a new hub assembly with the new bearing already in place. It is far easier to replace the entire hub.
Front wheel hub assemblies come in two variations, factory replacements and aftermarket. As this was my first failure, I opted for the factory replacement from the auto parts store. I was limited on time to make the event at Nashville Superspeedway, so I had to drive a distance to an AutoZone that had 2 hub assemblies in stock. Cost was around $91 each. However, if you have more time, they can be purchased online for almost half that amount.
The aftermarket hubs are quite a bit pricier and are marketed as the ‘last front hubs you will ever need!’ At $629 per side, they better be. However, they do seem to live up to that statement and you can read more about them at Good-Win-Racing.
Removing the Old Hub
Replacing the front wheel bearing/hub is a straight remove/replace operation. To remove the old hub, you must first remove the wheel, the caliper and bracket, and the brake rotor. The wheel lugs are 4 x 17mm and the caliper bracket is held on by 2 x 14mm bolts.
Now the hub is exposed and as you can see from the video, mine was shot.
Using a flat-head screwdriver, pry the silver cap off of the spindle to expose the spindle nut. The spindle nut secures the hub and bearing to the spindle. I had to tap the screwdriver into the edges to work the cap off.
The spindle has a slight indentation, and the spindle nut should have a slight deformation into the indentation. This prevents the nut from backing out over time. Using a pick or screwdriver, pry the indentation back up and use a 29mm socket to remove the spindle nut.
I used an impact gun for this part, but a breaker bar will work as well.
(Fun fact: the spindle nut on my car was only hand-tight and led to premature wear. One of the myriads of reasons I no longer let allegedly ‘reputable’ shops touch my equipment anymore.)
Issues with Removal
My wheel bearing ate itself and as a result, some ball bearings where split and deformed and I believe that caused additional damage to the inner bearing race. The inner race was stuck to the spindle, and I used an air hammer to knock it off.
Installing the New Hub
After removing the entire old hub assembly and stuck bearing race, clean the old grease off of the spindle with a rag and apply new wheel bearing grease. Then slide the new hub on and reinstall the spindle nut. Use a socket wrench to tighten the spindle by hand. This process will snug the rear of the hub to the knuckle stop, securely setting the bearing on the spindle. Use a torque wrench to tighten the nut to 120 – 130 ft-lbs. Finally, notch the outer ring of the spindle nut into the indentation of the spindle. A flat head screwdriver and mallet work well here.
(Note: Not pictured but worth noting, I used the air hammer to knock the abs ring off of the base of the new wheel hubs. My car doesn’t have abs and the ring removes easily.)
Once the new hub is installed and tightened, ensure it spins freely and with little resistance. Then replace the cap over the spindle nut. Finally, reinstall the brake rotor and caliper.
Swapping the Wheel Studs
This part is optional, but on the racecar, it is a must. Effectively, the wheel hub and bearing are swapped, and you are free to install the wheel and go about your day. But as you can see in the picture below, the lug nut engagement is less than ideal due to the shorter wheel studs on the replacement hubs. Compounded by the aftermarket wheels.
In my case, I swapped the wheel studs from the old hub over to the new. To do this, use a small mallet and tap the studs out of the old hub. Then, one at a time tap the shorter studs out of the new hub. When one was removed, I would slide the longer stud in its place. A stack of washers is then placed over the stud. The lug nut along with an impact gun are then used to snug the stud in place. It’s a quick and easy process and by doing the removal/replacement one at a time on the new hub, I was able to leave the rotor in place during the changeover.
Conclusion
There you have it. How to replace the front wheel studs on a Mazda Miata. With a few practical solutions thrown in for my case. This one was so easy I performed the work with the car on the trailer in about 15 minutes. And it ran perfect the next weekend at Nashville Superspeedway.
