1994 Pontiac Firebird Drivetrain

  • 180,000 MILES
My car has newer model chrome wheels from another Firebird [ 2000 ] All wheels and lug nuts are the same however, my left rear wheel keeps breaking studs and lug nuts wont stay tight, These wheels have been on the car for over a year, this problem with just the left rear started two months ago, I feel no vibration and no noise, car drives great, I am stumped.
Do you
have the same problem?
Saturday, July 6th, 2013 AT 9:05 PM

1 Reply

The first rule to avoid damaged studs is to use a click-type torque wrench on the nuts. That is so important that most employers will fire a mechanic after the second failure to do so. All shops have wall charts that list every manufacturer's torque specs for lug nuts for all of their models. Those numbers are published in their service manuals too. If you don't know the value for your car, a typical value is 95 foot pounds for steel wheels and a little less, like 80 to 85 foot pounds for aluminum wheels. Correct and even torque prevents other problems too.

The next thing is to look at any lubricant you used on the threads. First of all, never ever use any type of anti-seize compound on the threads. That will get a professional fired on the spot. The nuts will definitely work loose with that stuff on them. Some people put axle grease or wheel bearing grease on the threads. That can be okay if it's a very light coating, but you must walk the nuts on by hand and not use air tools. With nuts that have a tapered or rounded contact surface, running the nuts on with air tools will cause the grease to bunch up in front of the nut and centrifugal force will spin it out onto that contact surface. The grease can be on the threads but the contact surface must be perfectly dry and it has to match perfectly to the wheel surface. That friction is what holds it from coming loose.

Anodized studs have a light yellow, light blue, or silver coating electroplated onto them. There must never be grease used on them. That will dissolve that coating which is a lubricant. Anodized studs are used mostly on import vehicles but they might show up on any car.

The center hole of the wheel must match the axle hub. That holds the wheel centered. If the two don't match the job falls on the lug nuts and they aren't strong enough for that. This becomes even more important with cast wheels that use long nuts that don't have a tapered contact patch. Most of those also use washers under the nuts.

Once a wheel has come loose it must be replaced. That contact area gets chewed up and the nuts will never stay tight. You can tighten the nuts but each time they'll work loose sooner next time. Once they're loose the wheel will slide up and down with each revolution. At first that just grinds away more of the contact area but the constant bending back and forth will work-harden the studs until they snap.

When you replace studs you have to be sure they get pulled all the way in before installing the wheel. Spacers, like a couple of thick washers, must be used that have large enough center holes to allow the base of the stud to pass through it freely. Use an old lug nut or a regular nut and wrench to draw each stud in all the way. Install the wheel, then use the torque wrench on the new nuts, then again after driving the car a few miles.

If the car has rear drum brakes look at the stud holes in the drum to be sure they're centered on the studs. If each hole has a raised spot on one side, the drum was installed not centered at one time and the base of the studs hit the sides of the holes. The wheel would never have been tight and it would have worked loose.
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Saturday, July 6th, 2013 AT 10:12 PM

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