Talk > Automotive Social > 1992 Nissan 300ZX brake rotor reccomendation and advice.

1992 Nissan 300ZX brake rotor reccomendation and advice.

So, he blew out performance cross-drilled slotted rotors at 40K miles, and wants cheaper ones.

I'd recommend a change in driving habits of he can't afford rotors that will take his driving style.

She probably did not do anything seriously wrong in terms of driving habits. I suspect part of the reason the rotors on her car are warped is that she drives in a lot in the north Georgia and Tennessee mountain areas added to the brutal stop and go traffic in the metropolitan areas. She also takes lots of trips usually with one of her friends and they take as much stuff as they can with them, so the car gets driven at maximum gross vehicle weight a lot. I had told her previously to put on a set of Toyo Versado tires and the mileage to the wear bars was about what I and others have experienced with those tires. So I do not think she is an really abusive driver. I suspect that the original problem with rotors on her car is similar to the rotor problem Nissan's Infiniti division had with the Q45 when it first came out. It was an amazingly wonderful automobile, but was too heavy for the original designed rotors, and Infiniti got a lot of warped rotor warranty claims. It was never clear if the manufacturing process for the rotors was to blame or that the rotors design was too weak for the Q45.

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Incorrect fitting can distort (warp) discs; the disc's retaining bolts (or the wheel/lug nuts, if the disc is simply sandwiched in place by the wheel, as on many cars) must be tightened progressively and evenly. The use of air tools to fasten lug nuts is extremely bad practice, unless a torque tube is also used. The vehicle manual will indicate the proper pattern for tightening as well as a torque rating for the bolts. Lug nuts should never be tightened in a circle. Some vehicles are sensitive to the force the bolts apply and tightening should be done with a torque wrench.

Often uneven pad transfer is confused for disc warping.[citation needed] In reality, the majority of brake discs which are diagnosed as "warped" are actually simply the product of uneven transfer of pad material. Uneven pad transfer will often lead to a thickness variation of the disc. When the thicker section of the disc passes between the pads, the pads will move apart and the brake pedal will raise slightly; this is pedal pulsation. The thickness variation can be felt by the driver when it is approximately 0.17 mm or greater (on automobile discs).

This type of thickness variation has many causes, but there are three primary mechanisms which contribute the most to the propagation of disc thickness variations connected to uneven pad transfer. The first is improper selection of brake pads for a given application. Pads which are effective at low temperatures, such as when braking for the first time in cold weather, often are made of materials which decompose unevenly at higher temperatures. This uneven decomposition results in uneven deposition of material onto the brake disc. Another cause of uneven material transfer is improper break in of a pad/disc combination. For proper break in, the disc surface should be refreshed (either by machining the contact surface or by replacing the disc as a whole) every time the pads are changed on a vehicle. Once this is done, the brakes are heavily applied multiple times in succession. This creates a smooth, even interface between the pad and the disc. When this is not done properly the brake pads will see an uneven distribution of stress and heat, resulting in an uneven, seemingly random, deposition of pad material. The third primary mechanism of uneven pad material transfer is known as "pad imprinting." This occurs when the brake pads are heated to the point that the material begins to break-down and transfer to the disc. In a properly broken in brake system (with properly selected pads), this transfer is natural and actually is a major contributor to the braking force generated by the brake pads. However, if the vehicle comes to a stop and the driver continues to apply the brakes, the pads will deposit a layer of material in the shape of the brake pad. This small thickness variation can begin the cycle of uneven pad transfer.

Once the disc has some level of variation in thickness, uneven pad deposition can accelerate, sometimes resulting in changes to the crystal structure of the metal that composes the disc in extreme situations. As the brakes are applied, the pads slide over the varying disc surface. As the pads pass by the thicker section of the disc, they are forced outwards. The foot of the driver applied to the brake pedal naturally resists this change, and thus more force is applied to the pads. The result is that the thicker sections see higher levels of stress. This causes an uneven heating of the surface of the disc, which causes two major issues. As the brake disc heats unevenly it also expands unevenly. The thicker sections of the disc expand more than the thinner sections due to seeing more heat, and thus the difference in thickness is magnified. Also, the uneven distribution of heat results in further uneven transfer of pad material. The result is that the thicker-hotter sections receive even more pad material than the thinner-cooler sections, contributing to a further increase in the variation in the disc's thickness. In extreme situations, this uneven heating can actually cause the crystal structure of the disc material to change. When the hotter sections of the discs reach extremely high temperatures(1200–1300 degrees Fahrenheit), the carbon within the cast iron of the disc will react with the iron molecules to form a carbide known as cementite. This iron carbide is very different from the cast iron the rest of the disc is composed of. It is extremely hard, very brittle, and does not absorb heat well. After cementite is formed, the integrity of the disc is compromised. Even if the disc surface is machined, the cementite within the disc will not wear or absorb heat at the same rate as the cast iron surrounding it, causing the uneven thickness and uneven heating characteristics of the disc to return.

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Thanks. That information is new to me, but I was able to understand it. The improper tightening of the lug nuts is a strong possibility as she just recently had new Yokohama tires installed and she says the problem got worse after the new tires went on. Why do car owners have beg shops to use properly calibrated torque wrenches and lug nut tightening processes? It is like me having to remind them to properly refill the coolant system after they change the hoses. Yes, I had one of my cars returned to me as coolant system fixed from the dealer's service department with way too little coolant in it. Maybe the manufacturers need to make optically clear coolant tank windows part of the opaque coolant tanks they already use. Thanks again. I will have her go to a decent automobile service shop and have the wheels taken off. I will specify that they should carefully inspect the rotors, lug bolts and lug nuts, taking into account the information given and then reattach the wheels properly. Then road test. Now I have to find a decent automobile service shop in the middle of Georgia. That will be an interesting search.