Hi,

I have a 94 Ranger Xlt, 3.0, 5spd with 160K miles on it.
I use it for daily commuting and average about 320 miles per wk.

I put new front rotors on it 2 yrs ago. About 9 wks ago, the rotors were turned and new pads installed. Recently I noticed a noise (low freq-growl) coming frome the front when I apply the brakes. I jacked up the front and tested by spinning both front wheels, they both have a spot where the wheel will stop. So it looks like the rotors are "out of true" again.

What would cause this to happen so soon?


Is this a common trait with this model/year?

Should I take it back to the shop that did the work and have them re-do the rotors again?

Thanks,

Chrisj

 

One theory is that maybe the calipers are sticking for some reason and hence not "squaring" properly with the rotors, causing residual friction and then warping of the rotors. If the shop that did the pads didn't clean and re-lube the caliper slide pins, then that might be something to look into. It might be worth bringing it back to the shop and asking for another turn of the rotors, if they can handle it.

 

Chris, Rockledge's suggestion is quite possible. If the piston is sticking or isn't "true" to the piston bore, it can wear the rotors unevenly. Also, if the caliper doesn't "float" correctly, it will bind on one surface of the rotor and warp the rotors. Too, the rubber brake hoses can weaken internally and get a flap of rubber that actually acts like a valve and it will let fluid past the flap of rubber but not let it flow back against the flap when the pressure is released. That will wear and warp the rotors very quickly.

Also, on the later model vehicles, irregardless of make or application, if you notice, brake rotors are usually thinner--and, thus, lighter, in an effort to save weight--than they used to be. One downside to this is the fact that if the rotors are hot from heavier than common brake usage and one drives through a standing puddle of water, the cooler water will warp the hot rotors in a heartbeat!!

Finally, did the shop pack and load the wheel bearings CORRECTLY? If they did not, the rotor and hub and wheel assembly will rotate with too much freeplay or yaw and will wear out of round very quickly. In the same line of thought, if the bearings are not packed well, they will loose their lubrication pretty quickly and will overheat and bind the rotor as it spins in the caliper. It will, of course, heat warp them; even so, you will usually feel and hear that condition long before it wipes out the rotors.

I hope this is helpful to you.

 

In addition to what Loan Ranger has pointed out, something else to keep in mind is to make sure to torque the lug nuts properly, using the star criss-cross pattern and tightening them to 100 lbs/ft or so.

And braking habits can also contribute to rotor warpage. When possible, try not to ride the brakes to a complete stop and then hold them there. This tends to trap heat while at the same time resulting in pressure being kept against the hot rotors in one spot. I try to remember to allow my brakes the ability to "breathe" a little by letting off them a few times, especially during a strong braking session such as when coming to a stoplight at the end of an expressway.

 

I hate to throw a monkey wrench in this discussion but your rotors do NOT "warp". I know there is going to be a bunch of people that just grumble, but it is 100% true.

While it is true that you have to "turn" or "cut" the surface of a rotor to true it up, it is not because of wear. The uneven surface is a result of pad deposits forming on the surface. Think of it like a clogged artery. Once a small blockage forms it will cause a greater blockage as the deposit grows. With new rotors and new pads there is a "bedding" that has to occur for the brakes to work properly. This involves a proceedure to laydown an even layer of pad material on the surface of the rotor. Every mfg has directions on how they recommend you do this. It ususally involves a series of 10 or so "slow downs" from 60 to 5-10 mph that increse intensity with each pass that will heat the rotor evenly and transfer the pad material. This proceedure is rarely followed and offen results in a shaking steering wheel, or vibration, when you brake. This seems to be a much bigger issue with FWD cars, but it does occur. The other problem is shops and mechanic who don't understand how friction braking works, just throw out "your rotors are warped" and everyone buys it. Unevenly heated rotors cause deposits to form, then if the deposit goes unchecked it grows. Pretty soon the heat/friction + pad material + iron rotor will cause it to change to Cementite. A very brittle iron compound, and a poor disapaiter of heat. This is a bad thing. What is worse is if you have Cementite deep enough into the rotor you may not be able to turn/cut it out.


This first link is a very detailed article, written by well known name in the racing world. The other links are just supporting info.

http://www.stoptech.com/whitepapers...rotors_myth.htm

http://www.baer.com/Support/TechTips.aspx?TechTipID=4
http://www.baer.com/Support/TechTips.aspx?TechTipID=5
http://www.stoptech.com/faq/data/faq25.htm
http://www.stoptech.com/faq/data/faq26.htm
http://www.hawkperformance.com/faq.cfm#Q3