That makes sense. Another thing to check out.

 

No it's very irregular and will change with brake temperature. A warped disk will tend to be present at all times and just get worse with speed.

 

In your opinion would it be helpful to try bedding the pads again?

 

If its the caliper.....Cobalt has a set fully refurbished for sale.....

 

OK just thought I'd mention it as I know a few people had feared the worst only to find out that they had forgot to torque the nuts up after removing a wheel.

Out of interest, do you feel the vibration through the brake pedal at the same time as the steering wheel vibrates?

 

I only feel it in the wheel. Shakes at least an inch.

 

I would jack up the front and check the wheel bearings: grab the tire at 12&6 and wobble for play, you should have virtually none. If you do turn the tire to 3&9 ad do the same, having someone hold the steering wheel firmly. If you get a significant difference look to worn suspension parts. If all is well back to the brakes.

First check the runout of the disks, pull the pads, a dial guage against the surface is the right way but in a pinch setting a screwdriver against the disk on the caliper or an immovable base (jack stand bottle jack etc) rotate the disk and feel for a continuous rubbing. If you get variations most likely you will need a surfacing. Check the inner outer and middles of both sides.

If they aren't warped and lacking Kais set of aggressive pads to scrub the rotors the next thing to do is pull it apart and take the rotors to be surfaced...

Then careful follow the pad mfgr process for bedding to minimize the potential for it happening again.

 

yes 100%.

Given them death from high speed to medium speed without stopping and let them cool between almost stops. If that fails its something mechanical.

 

Had a similar issue. My calipers were toast. Hopefully your issue is far less expensive

 

Did you have them rebuilt? The kits are about $40 each, and it's 4 kits per caliper.

 

The 964 uses angular contact wheel bearings so does this test really apply?

 

Good source for a caliper rebuilt kit and maybe a diy link?

 

Haha i used it as an excuse to go big. Why repair when you can upgrade. Amirite?

 

Most do. All you're looking for is excessive play.

 

I had bad vibration from the front end which started in Spa with disc approaching 1000 miles old and pads the same. The vibration got worse the more laps I did (the hotter the brakes got). For road use the vibration was noticeable but not excessive.

Did another track day - same pattern as Spa, got worse the longer I used them.

Got the brake discs skimmed (on the car) and never a problem again.

Hope that helps a little with your diagnosis.