warped rotors - diagnosing

Dial indicator.

|In article |, | snipped-for-privacy@vianet.on.ca (Cameron) wrote: | |> Hi |> |> I've got a 2000 windstar, 44,000km on it. When applying the brakes |> there is a pedal pulsation and a audible "dub dub dub" sound which |> slows as the van decelerates to a stop. Now a while ago I took the |> calipers off, check the pads, lubed the sliders etc and things looked |> good. I did notice a tiny bit of this same sound and slight pulsation |> but had put it down to the oil guy who rotated my tires and using an |> air gun to reinstall the tires. When I reinstalled the tires after the |> brake work and torqued them properly the sound seemed better. Now that |> I've got my snow tires on the sound/feel is more obvious. |> |> So, I'm wondering if the rotor is warped and how to diagnose this. I |> understand that if it is really warped it'll be quite noticable (rusty |> spots, obvious bend etc.) but if it is slightly warped will placing a |> straight edge on the rotor be able to tell the warping? |> |> What is the best method to do this? | |Dial indicator.

....mounted to a jackstand or even a magnetic base on the caliper mount. Check both sides. One side could be warped and the other straight, if it's a vented rotor. Rex in Fort Worth

It's warped and you've already diagnosed it. It is the only moving part in the brake system that rotates in relation to vehicle speed.

Get a set of four new rotors. If you don't go out of your way to get ripped off (like buying from a dealer), it shouldn't set you back more than $300.

My point was that it shouldn't come to more than $300 unless you go out of your way to get ripped off, like at a dealer.

rule of thumb: if you feel the shake in the steering wheel, it's the front rotors. if you feel it in your seat, its the rear rotors.

when you look at your rotors, see if there is one blue spot or rough spot, and that's a sure winner.

also, proper torquing with an impact wrench will NOT cause rotor warpage.

What if you don't feel it in the steering wheel or the seat back but instead you feel vibration in the brake pedal? How do tell if it's being induced from the front or rear?

I realize pulsation (runout) can be diagnosed with a dial indicator but what about vibration. It can come from hubs, wheels, calipers, rotors and from front or rear?

"MudPuppy1976

You're feeling the pads being jostled by the rotors.

I recomend replacing all four.

Maybe you should just have a mechanic repair your car.

I took a 98 LeSabre to CarX for brakes. There was nothing wrong with them, but with 95000 miles on the car, I just wanted them replaced. They put new pads on and said I needed rotors as they were warped and wouldn't be legal after cutting. Okay, I said, put the new rotors on. Everything was fine for about three days and then they started pulsating like crazy. I took it back, and they said "there must be a caliper sticking". They warranteed the rotors, put on another new set, and replaced the calipers. I paid for the calipers only this time. (Yes, I was stupid). After a week, the pulsating returned. I didn't dare touch the brake pedal at higher speeds, it was so bad. I decided to take it to Buick and tell them the history. They took the front wheels off and showed me where rust builds up on the hub, and if it is not cleaned up during a brake job, the results are exactly what I experienced. They cleaned them up, turned the rotors true again, and I never had any further trouble. The mechanic at Buick also told me that the quality of aftermarket rotors is much less than GM's. Since he didn't try to sell me new rotors, I guess I'd give him the benefit of the doubt on that.

So CarX bent over backwards to make me happy, and I don't hold any malice toward them. I learned, however, that maybe these days the dealer mechanics are a better way to go. Yes, I spend too much but I'm 51 years old and hassles are more of a pain in the ass now than they used to be.

Don't know if this'll help you or not, but hey it didn't cost you anything either.