NA Front Hub/Bearing Replacement

By Jason Hupka - jason_hupka@yahoo.com

Description: The front hub/bearing assembly on an NA model Miata is a one-piece unit consisting of the hub/lugs with the bearings pre-installed and greased. The assembly is typically considered non-serviceable, and you replace the unit when the bearings fail.
Symptoms: In my case, my 1990 Miata developed a thunk-thunk-thunk type sound on the front right wheel while driving. It sounded very similar to driving over a concrete highway with the relief cuts in the road - just a repetitive thunking sound. The sound got louder when making left hand turns, and pretty much disappeared when making right hand turns. Based on forum searches, I determined it must be a failing bearing causing the issue. I had about 118,000 miles on the odometer when I did this service.
  • New Hub/Bearing Assembly - The Timken brand part I used was about $110 from AutoZone. Get two if you're doing both sides and shop around - different parts stores had wildly different prices.
  • New Hub Nut - About $5 from the dealer - Get two if you're doing both sides. I opted to reuse mine, but a new one is suggested since the nut is deformed with a punch into a keyway on the spindle. Repeated use of a used nut could over-fatigue the fastener.
  • Wheel Bearing Grease (for spindle)
  • High-Temp Grease (for brake parts)
  • Anti-Seize compound

** If you need new brake pads, now is a great time to do this service as well since you will have everything apart to do the brake work.

Note from Sean Johnson: I'd like to add the dust cap to the list of the parts needed for the change. It's a part that can be difficult to remove without warping it.
The caps aren't available at places like Autozone, Advance, or O'Reilly's, so it's better to have a spare than have to go looking on Sunday afternoon.

  • Car Jack/Lug Wrench and Jack Stands
  • 14mm Socket (for lower caliper bolt and caliper bracket bolts)
  • 17mm Socket (for upper caliper bolt)
  • Length of wire (for wiring the caliper out of the way)
  • Hammer (for knocking out hub nut cover and hitting the punch/chisel).
  • Slotted screw driver (for hub nut cover)
  • Punch/Chisel (for hub nut tab)
  • 29mm Socket (for hub nut)
  • Cheater-bar or pipe (to help remove highly-torqued hub nut)
  • Torque Wrench that can measure 120 ft-lbs to 150 ft-lbs
  • C-Clamp or Channel Pliers (something to use to compress the disc brake piston)

First, loosen the lug nuts of the front wheel while it is still on the ground so you don't have to fight the spinning wheel while it is jacked up. Next, jack up the side of the car you will be replacing the hub on. Even though you won't be under the vehicle, put the car on a jackstand for stability since you could be shaking the car a bit working with the tight bolts in later steps.
Remove the lug nuts and wheel, and then remove the upper and lower slider bolts for the caliper. The lower bolt is 14mm and the upper bolt is 17mm. The red arrows point to where the caliper bolts were (the caliper and caliper bolts have already been removed in this photo).
Using a piece of wire, hang the caliper out of the way with it - do not let the caliper hang by the brake line. The lower control arm makes a nice place to set the caliper, but chances are you'll knock it off, so make sure you wire it to the coil or other suspension component so no stress is placed on the brake hose.
Remove the spring clips that hold the pads away from the caliper, and remove the brake pads.
Remove the two bolts that hold the caliper bracket to the spindle assembly. Both of these are 14mm bolts, and the yellow arrows point to them. Once the caliper bracket is off, you will be able to remove the disc rotor (up until now it has been loosely attached to the hub assembly since the lug nuts hold it tight).
Next, use a slotted screwdriver and hammer to pry the cover that is over the hub nut. This can be in there tight, so it may take a bit of persuasion to get out.
Using a metal punch or chisel, knock out the indentation on the hub nut that is sticking into the spindle keyway.
Slip a pipe over the handle of your socket to get the leverage needed to easily remove the hub nut (or use some equivalent method). The hub nut needs a 29mm socket to remove it. I used a four-foot pipe and my five year old could have removed the nut with that much leverage.
Remove the old hub/bearing assembly from the spindle. Wipe off all old grease and any debris from the spindle, and apply some new bearing grease to its surface.
Here's a picture of the shiny new hub and bearing assembly.
Here is a picture of my old bearing (not the best focus). You can see the grease squeezed out from the bearing race. I'm not sure if this is normal, but to me that looks like one reason why it may have failed.
Place the new hub part onto the spindle, and screw down the new hub nut. Using a torque wrench, torque the hub nut at 125 ft-lbs to 150 ft-lbs. It is pretty important to get this nut torqued down - if it is too loose pre-mature bearing failure can occur. Plus, this nut is the main mechanism for holding the wheel on the car. Since I reused my hub nut, the part that was indented lined back up with the keyway on the spindle. For me, this was a crosscheck that I was doing things right.
Using your punch or chisel, place a dent in the hub nut rim so it protrudes into the spindle keyway. This will prevent the nut from loosening on the spindle. Also, replace the hub nut cover removed earlier
Reassembly is basically the reverse of what we've done so far. So, place the disc rotor back on the hub and bolt the caliper bracket back onto the suspension. The caliper bracket bolts are torqued at 36 ft-lbs to 51 ft-lbs. Grease the 'ears' on the brake pads with high-temperature grease meant for brake parts, and place those back in the guides in the caliper bracket. Also, don't forget to put the pad springs back on the pads to hold them away from the rotor.

** If you need new brake pads, now is a great time to do this service.
Next we'll have to put the caliper back over the pads. It is a bit easier if you compress the caliper piston. So first open the brake fluid reservoir under the hood...
...Now use some channel pliers or a c-clamp to push the piston back into its housing. Be careful not to damage the rubber seal around the piston. You can even use the specific piston-tool for this if you're feeling fancy. Once this is done, place the caliper over the pads, and put the cap back on the brake fluid reservoir under the hood - you want the fluid exposed to moisture in the air the lease amount of time possible.
Now clean off the caliper slider bolts of any old grease/debris and re-apply more high-temp brake grease. Tighten those bolts back into their respective slots. The caliper bolts are torqued at 58 ft-lbs to 65 ft-lbs.

Place the wheel back on the car and tighten the lug nuts in a cross pattern at 66 ft-lbs to 86 ft-lbs. Make sure to apply some anti-seize compound to the lug threads before putting the nuts on.

(Editor's note: Miata.net does not recommend use of anti-seize compound on wheel lugs.)

If you're doing both hubs, repeat this process for the other side.


Note from Mack Bailey:

I had just this year replaced my brake pads and I didn't want to go through all that again (with the springs, clips, bleeding brakes, etc.) for the hubs, as Jason instructed. I was able to just remove the two 14mm cap screws holding the calipers, remove the locking nut on the spindle, and pull the hub, rotor, and brake off as one. The hub then can be removed from the rotor (with rotor still "inside" caliper) and replaced. Care still needs to be taken not to put stress on the brake hose. I completed the job in less than 1 1/2 hours, not counting the trip to Sears to get a 29 mm socket for the locking spindle nut. The hardest part was getting the "dent" out of the locking spindle nut -- AND remembering that the hub goes back in with the lugs pointing OUT!

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15 August, 2010

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