Cowl shake while braking above ~45mph

Not sure if this is the right forum as we don't seem to have a general Troubleshooting or Brakes subforum, but here goes...

I noticed this for the first time today. I was driving on the freeway and when I applied the brakes the whole front of the car started to shake. Cowl shake. Steering wheel oscillating --- shaking back and forth at a high frequency. This happened under light braking or hard braking. As I exited the freeway on the off-ramp, the shake went away completely below 45mph. At city speeds, no matter how much brake pressure I use, there is no shake.

TL;DR --- Above about 45 to 50mph, any application of brakes will cause my steering wheel and the front-end of the car to shake.


So.

My best guess is that my rotors are ever so slightly warped. Anyone else? This might be a perfect excuse to upgrade to a BBK. Yes, I know it's more bling than anything but... Hehehe.

Does sound like a rotor issue.

I agreed it could be Rotors...however, when was the last time your brakes were serviced?....as sticky brake pad will cause brake vibrations too.

Bram

Are you on stock brakes?

What was the condition of the pads & rotors last time you took the wheels off?

Don't rule out your wheels. That was my issue... Hit any potholes lately?

I am still on stock calipers and rotors. I have not hit any potholes recently. I'm pretty certain sure my wheels are fine. The rotors, though, I am not too sure. I only recently bought my car (back in the summer) and haven't done anything to the brakes since beside checking pad wear (they have plenty of material left). I suppose I could swap in some new pads and check that way...

do some hard braking to warm things up.....google or search brake pad bedding in procedure and see if that helps or does nothing.

A warped rotor is super easy to check for with the use of a dial gauge. You can also jury rig a fixed probe next to the edge of the rotor and spin the rotor and watch the gap between the edge of the rotor and the probe - harder to get a good read on the problem than using a dial gauge. I have only had one incidence of a bent rotor (not the NSX) and you could definitely feel it through the brake pedal. As the rotor moved sideways it pushed back on the caliper. At lower speeds the caliper slides back and forth on the mount (floating caliper system) and you don't notice the pedal pulse. At higher speeds the pedal pulsing starts to become noticeable. If you don't feel any pedal pulse at highway speeds with hard application, it might not be a bent rotor. The dial gauge is the only sure indicator and its a relatively easy test to set up.

Perhaps look for rust spots on the surface of the rotor which can be caused by metallic pads if the vehicle is left parked for a period of time during high humidity conditions. The rust forms where the pads contact the disk surface and then the pads grab on the spot when the brake is applied. Normally wears off with some use. The other things to consider are bent tie rods or severe alignment problem.

Butters said:

I am still on stock calipers and rotors. I have not hit any potholes recently. I'm pretty certain sure my wheels are fine. The rotors, though, I am not too sure. I only recently bought my car (back in the summer) and haven't done anything to the brakes since beside checking pad wear (they have plenty of material left). I suppose I could swap in some new pads and check that way...

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Sounds like a cheap fix. New rotors and pads from sos. 1/2 a Saturday, beers, and smooth braking to follow.

Thanks for the all the advice, guys. The car had been sitting for about two and a half weeks in a garage that is secured but not shielded from the elements. Right after I started this thread I went and did some more driving around town and on the freeway and the issue seems to have gone away. Curious, but in the future should it show up again, I'll be sure to pay attention to applying the brakes and warming them up to see if the problem goes away. Either way, be it rotors or pads (as it likely would be), [MENTION=31260]Jinks[/MENTION], you're right ---- cheap and easy fix.

O'reily auto parts resurfaces rotors for very responsible. They even did my Stoptech slotted rotors, although the manager I think had to take that on because everyone else was saying no and he chimed in.

tire problem?

Hmm, sounds like a possible tire issue since the problem went away after driving for a while. Old tires that had been sitting for a while would develop flat spots where they'd been supporting the weight of the car.

I went through a similar issue. My rotors & pads were fine. Get your brakes checked, and don't just spend money on parts that may be fine.

Butters said:

Thanks for the all the advice, guys. The car had been sitting for about two and a half weeks in a garage that is secured but not shielded from the elements. Right after I started this thread I went and did some more driving around town and on the freeway and the issue seems to have gone away. Curious, but in the future should it show up again, I'll be sure to pay attention to applying the brakes and warming them up to see if the problem goes away. Either way, be it rotors or pads (as it likely would be), [MENTION=31260]Jinks[/MENTION], you're right ---- cheap and easy fix.

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