Slight pulsation from brakes at 70+ MPH (Replace rotors?)

Question

my pads have about 25% life left, I am going to replace them soon and Im wondering, should I replace my rotors as well?

Im feeling a very slight pulsation at 70+ MPH (when braking only). But braking at lower speeds or 30MPH or 50MPH the pulsation is non-existent.

The pads/rotors were budget house brand and the cheapest available products from NAPA auto-parts. If i were to upgrade to higher quality rotors would there be any real difference than me machining/shaving the rotors i have now? I believe the rotors to be in good condition and the slight pulsation I presume would disappear after a fine machining I'm just curious if upgrading to better rotors would give any real increase in braking.

Answer 1

One of the factors that influence the cost of replacement rotors is mass. Basically we are talking weight. Over the last couple of decades rotors have gotten cheaper and lighter. The rotor is lighter because it has less material. I buy the heaviest rotors I can get the specs on. This was actually part of a marketing campaign by NAPA several years ago. They had cutaway rotors on the counter to show how much thicker and heavier their rotor was. In my experience rotors of the 60's and 70's would last the life of the car as long as the pads didn't wear to the point of metal to metal contact. In many cases the same rotor was used in nine passenger wagons (impala wagon) that they used in compact cars (Novas). In most cases they were larger than they needed to be. They weighed a lot. They were made with some extra material. Granted cars were worn out at 120,000 miles but you could get at least one and sometimes two resurfacings out of a rotor. Any rotors I have had turned recently seem to warp before the pads are at 50%. Part of the reason is that pads are smaller and more aggressive so they generate more heat and wear the rotor surface. This heat is what causes the rotor to warp. The thinner the rotor, the easier they warp.

Answer 2

You really aren't going to "upgrade" to higher quality brake rotors, unless you spring for some carbon fiber ones, but those are pretty much for performance and race cars. For average every day use, you can buy the cheaper rotors and have no worries about them. They will last for as long as you need them.

As for your question, considering the cost of new rotors versus the price of getting rotors machined, it makes sense to buy the new rotors. In most cases, the new rotors will only cost you a few dollars more. It makes sense economically if you consider your time spent getting the old rotors to the a shop to get them turned, then waiting on the job to be done or expense of driving a car home, then having to come back and get them. By purchasing the new rotors, you do it all on your time. Many still choose to get the old ones resurfaced and this is not a bad option as long as the old rotors are thick enough to be within manufacturer specification. Along with what I said, though, I almost always replace the rotors at the same time as the pads to alleviate any bad situations which may arise and to save myself some time in the process.

If you do purchase new rotors, ensure you use some brake cleaner and clean off the surface areas of its protective coating. If you don't, your new brake pads will get gummed up with the stuff and not work very well.

Whether you purchase new or resurface your old rotors, ensure you bed the new brakes properly. This was covered extensively in covered by Centric Parts here.

Answer 3

The pulsating can be rotors or unbalanced wheel lug torque, among other things.

The various "grades" of rotors that NAPA, et al. sell are all going to be about the same. Same with the pads. Most of the "grading" is marketing gimmicks, although with pads there can be some pros/cons with each.

Anyway, if they are still within spec after machining the rotors are fine to use. Getting a new pair to use while machining the old ones at your leisure is not a bad idea, just be sure to coat the old ones with WD-40 or something before storing them (and clean it off before installing!).

Answer 4

does it feel like an abs pulsation?? but much more light? sometimes a bad wheel sensor can cause the abs to pulsate during braking. most likely it is a rotor that is slightly out of round that is much exagerated at high speeds. i would check all wheel sensor readings with a diagnostic tool if the rotors are not out of round and with in spec.

Answer 5

Try bedding the pads. Sometimes the pads need to transfer more material onto the rotor surface to get better adhesion. Find an empty road and get up to about 50-60, and then hit the brakes medium-hard without going into ABS (make sure it is pretty hard). Do not stop. Slow the car to about 20mph. Cruise and cool the brakes for about 2 minutes. Then repeat the process 2 more times. Then cool the brakes down for about 10 minutes. Then you are done. Then see if the problem is still there or not. If so, get some new pads and have the rotors checked for warping. I do not recommend ever upgrading rotors. I do recommend upgrading pads to performance street pads.