# Car Question **URL:** \ **Category:** Factual Questions\ **Created:** [September 19, 2005, 8:06am UTC](https://boards.straightdope.com/t/car-question/322339 "2005-09-19T08:06:10Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Btrenary](https://avatars.discourse-cdn.com/v4/letter/b/919ad9/32.png) [@Btrenary](https://boards.straightdope.com/u/Btrenary)\ **Post date:** [September 19, 2005, 8:06am UTC](https://boards.straightdope.com/t/car-question/322339/1 "2005-09-19T08:06:10Z")
I had my brakes serviced at a local AAA station. And by serviced I mean all rotors and pads were replaced. So here is my question. When I brake there is a definite pulsating grinding noise that is happening about 80 percent of the time. I just went for a test drive with a guy from AAA and he can’t figure it out. They assure me that my brakes are new. I called a local Ford dealership (I drive an explorer) and they said that one or more roters might be out of alignment. I don’t know who to believe. Has anyone heard of this problem? ---
**Author:** ![surlyprince](https://avatars.discourse-cdn.com/v4/letter/s/8baadc/32.png) [@surlyprince](https://boards.straightdope.com/u/surlyprince)\ **Post date:** [September 19, 2005, 9:10am UTC](https://boards.straightdope.com/t/car-question/322339/2 "2005-09-19T09:10:36Z")
The wheels are probably over (or unevenly) torqued. This will cause the rotors to warp. That or they never really replaced them. That’s all I can come up with at 2am. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [September 19, 2005, 11:48am UTC](https://boards.straightdope.com/t/car-question/322339/3 "2005-09-19T11:48:36Z")
It is possiable that a brake pad was put in backwards, so the pad is against the caliper and the back is what is against the rotor. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [September 19, 2005, 2:01pm UTC](https://boards.straightdope.com/t/car-question/322339/4 "2005-09-19T14:01:16Z")
When I first met Mrs Geek she would not let me work on her car (a Nissan Stanza, btw). Once she got the brakes changed at Sears and they did exactly what the OP described. There was a grinding noise and you could feel something wasn’t right in the pedal. She went round and round with Sears. They kept focusing on the rotors and would do everything but put new pads on it. Finally, I went down to the local auto parts store and got some new pads and the problem went away. I know someone else with a Nissan who had exactly the same problem. Apparently you can’t put the cheaper brake pads on Nissans. Might be something similar with your car too. I think they are all using semi-metallic brake pads these days. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 20, 2005, 3:33pm UTC](https://boards.straightdope.com/t/car-question/322339/5 "2005-09-20T15:33:31Z")
I think that **surleyprince** got it in one. Pulsations are caused by the brake rotor moving latterly against the brake pads, causing them to move in and out. This causes the brake pedal to pulsate. This can be caused by: [ul] [li]warped rotors[/li][li]rotors that were mounted incorrectly (rust on hubs)[/li][li]rotors that were mounted to warped hubs caused by overtorquing wheel lugs[/li][li]rotors that were overtorqued[/li][li]rotors that were turned, and the lathe was out of spec[/li][/ul] The rotors have to run true, lateral run out will cause problems. On the cars I teach on, acceptable run out is measured in thousands of a millimeter. Other cars are not that sensitive, but lateral run out is always a concern. As far as the noise, it could be cheap pads, it could be a lack of anti-squeal product on the back of the pads, or it could be an a symptom of the pulsation mentioned above. Without having the car on my rack, I cannot give you a definite diagnosis. But, bottom line, pulsations should not be present after a brake job. Brake jobs should cure pulsations, not cause them.