Mechanics

WHY IS THIS HAPPENING?

2001 Nissan Maxima • 920,000 miles

My car has a extremely annoying issue. When ever I turn the wheel to the right when moving thier is a high pitch scweell and it is annoying as shit. I belive it is the dirt cover for the back of the roater but is there something im missing? Also if its the dirt cover rubing against the rotor is it ok just to wedge a screw driver in there and bend it back? Thanks
Jeremy
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Jermx101
March 16, 2012.



It is very common for splash shields to bend and rub. They're just sheet metal, (except on Fords; they use plastic). You can usually bend them back by hand. 1/4" clearance is typical.


Caradiodoc
Mar 16, 2012.
Sweet um I dont have a torque wrench is it still fine to just tighten the nuts on the wheel with a regular wrench and if so how much do I tighten them?


Tiny
Jermx101
Mar 16, 2012.
You don't have to remove the wheel to bend the splash shield. Just reach underneath and tug on it.

As for lug nuts, the use of a torque wrench is very important, especially on front-wheel-drive cars. Without one, you have to rely on common sense. There are four reasons for setting the proper torque. 1) The nuts won't work loose while driving. 2) A 90 pound weakling will be able to get them loose to replace a flat tire. 3) The threads will not be peeled off or stripped. 4) Uneven clamping forces will promote warping brake rotors from the repeated heating and cooling cycles.

Over-tightening the lug nuts will damage the threads, but you won't know about that until the next guy comes along to rotate tires or replace them. Then he is the guy who unfairly gets the blame for the damage.

Another do-it-yourselfer problem is caused by using grease on the studs. It's acceptable to use a very light "taste" of axle grease on the threads of regular studs, but most import cars have studs with an anodized coating. That is an electroplating that makes them look light blue, light yellow, or silver. That coating is a lubricant already, and no grease must be added. Grease will dissolve that coating.

When you do use grease on the threads, it must be very little and you must run the nuts all the way on by hand, (no air-powered impacts), then torque them to specs. When do-it-yourselfers put a big wad of grease on there, then run the nuts down with an impact, the centrifugal force will spin the bunched-up grease onto the tapered friction surface where the nut contacts the wheel. That contact surface is what keeps the nut from working loose as you drive, and you don't want any grease in there helping it to come loose.

Every manufacturer has published torque specs for their lug nuts. All tire and alignment shops have wall charts with those numbers for reference, and they will gladly tell you your numbers over the phone. I was always happy to find that information because it showed the owner was doing a conscientious job and they were aware of the importance of doing it right. If you can't find the information anywhere else, use 80 foot-pounds as a starting point. The torque is calculated from the diameter of the studs, and is adjusted down for anodized studs and for cast wheels. All 9 of my Chrysler products call for 95 foot-pounds but they all have steel wheels and standard studs. 80 foot-pounds is common with cast wheels.


Caradiodoc
Mar 16, 2012.
Thank you Very Much 1 more question. The brakes on the front of the car are screwed up. When you break it feels like the calaber is only catching the rotor at one point which causes the car to shake back and forth. It is ablolutley horrible when your on the freeway because it is very hard to keep control. What is this and is it something that is important to get fixed or can we live without fixing it. Also if you know does this cause additional damage?


Tiny
Jermx101
Mar 16, 2012.
That is due to a warped brake rotor and is very common on any car. (Reread number 4 in my previous reply). The fix is to have it machined which is also a normal part of any regular brake service.

I made some sad drawings to show the two kinds of warpage. In the left drawing, the mounting surface, (blue arrow), and the two sides of the friction surface, (green and red arrows), are all perfectly parallel. That's necessary for smooth braking.

In the middle drawing, the friction surfaces are still parallel but they are not parallel to the mounting surface. This is what happens from uneven heating and cooling, especially splashing cold water up onto the rotor when it is hot, and that will be greatly aggravated by uneven lug nut tightness. The brake caliper will slide sideways back and forth for every wheel revolution and will tug on the steering linkages. You'll feel that vibration in the steering wheel and seat but not in the brake pedal unless the warpage is severe.

In the right drawing the two plates, or sides of the friction surface are not parallel to each other. As the rotor goes around, the brake pads have to move in and out to maintain contact. When the thicker area comes around, it pushes the brake pad and piston back into the caliper which pushes brake fluid back up to the master cylinder where it pushes the brake pedal back toward you. You'll feel that as the brake pedal rising and falling with each tire revolution. It will often be felt in the steering wheel too but the brake pedal gets all your attention. These drawings show everything greatly exaggerated. It only takes a few thousandths of an inch thickness variation to be felt. That's less than the thickness or two sheets of paper.

There is a legal minimum thickness a brake rotor can be machined to, and every manufacturer publishes those numbers. It can be allowed to wear to a certain thickness, but the "machine to" specification is usually.030" thicker. That means a rotor can be thick enough to legally remain on the car but not thick enough to legally machine it to remove the warpage. In that case they must be replaced. Fortunately new rotors usually aren't very expensive.

There are a few tricks professionals do when installing new rotors to reduce the chance for noises and vibrations but often new rotors will still warp in a few months and have to be machined. This is more common with the less expensive Chinese rotors. There's nothing wrong with the part itself but when we make parts here out of cast iron, we let them "age" for about 90 days, then perform the final machining. Chinese parts are cast, machined, packaged, and shipped right away, then they age on your car and often warp. One machining is all that's needed, then they typically don't cause a problem after that as long as you wait long enough for all the warping to occur before having them machined.


Caradiodoc
Mar 16, 2012.