Bought a used 2000 Miata that has started making an oscillating moaning sound in the driver side front at speeds over 40 miles an hour. Took off the wheel to discover the dust cap is missing from the hub nut. No history of maintainenece for the problem. The staked lock washer looks new. If the hub nut was not torqued to 167-215Nm for factory spec. pre-load, would this moaning sound be a tip off? I have yet to test the wheel bearing lash/freeplay with a dial gauge. Does anyone have experience with this troubleshooting sound effect? Thanks in adavance for any enlightenment.

 

i've not had this prob in the past. IMHO it seems that dust and dirt would be able to get in the wheel bearing (not to mention grease getting out) with out the dust cap installed. i'd replace the bearing assy and install a new dust cap as the old one prob got messed up when removed (why it's not installed). if money is tight pull the assy off and check the spindle to look for the bearing race spinning around the sipndel (it will look like someone took a file to it), it should not.

if the nut was too loose it could make noise and jack up the race. if it's too tight, the bearing will not have enough room to expand and will fail REAL fast. either way sounds like you might need a new bearing.
before you do anything with the bearing, pull off the wheel and make SURE the dust shield is not rubbing against the brake rotor, i've seen it before, just bend back. good luck.

 

Thanks for your reply and wisdom. I had a chance to sneak the car into a service bay during the holiday and give it a complete inspection. Indeed the front left wheel bearing was bad on the outside bearing. Replaced it with no problems. I found a leaky clutch slave cylinder that is next on the list. I could not get any parts over the weekend for that problem so the luxury of a lift will be sorely missed for this next repair.