JakeMate

Got zero responses on the 996 board for this question....so I figured you guys may be able to help.....

Brakes are working great below approximately 90mph. Above 90, when applied, I'm getting a vibration and a bit of a grinding feel.

Using stock pads currently. They look like they have a fair amount of material left. They have about 8,000 miles on them. They have two track events and a half dozen aggresive driving days. The rest of the mileage is normal driving.

Checked the rotor thickness recently. They were right in the middle; between new and minimum thickness. Pretty sure they are original rotors (I'm second owner). The vent holes have a bunch of crap in them. I've never cleaned them out. I have about 24,000 miles on the clock.

Recently changed brake fluid to ATE super blue. (Better pedal feel after that.) Haven't gotten the brakes hot enough to verify my fading problem is gone that I experienced at the last track event, but I'm pretty sure it was the fluid.

Time for new pads maybe?
Turn the rotors if I can maintain above minimum thickness?
How are Pagid Orange pads?

There is some visible pad deposition on the front rotors. This is from washing the car and letting it sit without driving it for a few days. I leave the parking brake off but the pads still slightly touch the rotors and leave a bit of deposition in the shape of the pad. In the future, I'll take the car for a spin after a wash. I cannot feel this deposition though. Could this be the culprit?

Thanks guys.

AW

"The vent holes have a bunch of crap in them. I've never cleaned them out. "

This may explain the situation. Brake friction creates some gas. Without the rotor holes, excessive gas probably pushes back on your pad until enough pressure has escaped, creating the vibration you describe.

Pagid orange pads are OK and noisy when cold, fantastic when hot. The only issue is that are very hard on your rotors.

AW

macfly

Last year I did a lot of development work with StopTech on a big brake kit for the Z8. They are a great company and you can share in their knowledge of braking on their website, www.stoptech.com look in FAQ and technical sections.

I had something a little like this at one point, and they put on a very abrasive pad set for a couple of laps to 'smooth' out any uneven deposits. You could try this if you have access to a good brake shop. It worked for me in that instance.

I know it is very important to keep the vent and holes clear for even cooling, after every set of laps you should blast them out with compressed air, but I am not sure this would cause your vibration.

The ATE Blue and Motul 6000 are both great and eliminating fluid boil.

I tried Pagid Orange, they are a slightly 'high maintenance' pad, they require re-bedding in before every track event, or every few hundred miles if they are just getting normal road use. They are designed to work at the higher temperatures generated at the track, the trade off is they aren't so good at lower temps. For mostly road driving the Pagid Blues are easier to live with, and quieter, but if you do long track sessions on a brake intensive track they will exceed their design max after 10 laps or so.

Having been thru this at great length last year I have learnt that there is no perfect pad, the braking equivalent of a 0-55W oil just doesn't exist. You have to pick your pads by the operating temperature range you want them to work at. Remember each time you swap your pads you'll need to re-bed in the new set on your rotors.

As to skimming the disc, it may help clean the surface, and is a good idea, but also check all the suspension bushings and bearings, as this kind of high speed vibration may be nothing to do with your brakes at all, but merely showing up by the pressures exerted by them at those speeds.

JakeMate

Thanks for the advice guys.

Very good info at the Stoptech site. Everyone should read the section about pad material deposition on the rotors and how to avoid it.

Larry Herman

You probably have uneven material transfer (like the article says). One trick that I would do on my Carrera was to warm up the rotors (a few gentle stops) and then completely wet them down and let the car sit overnight. The rotors will develop surface rust. Then take the car out a do a few firm, but not crazy, stops to clean them off. This has always worked for me and I DE'd & Club Raced that car for years on the same rotors.

enthusiast

Good advice here. When I have build up on my brake disks I feel it at all speeds, so as someone else stated you may have a suspension issue not a brake issue.



It may be hard to get the brake disks machined correctly and for what they cost I wouldn't do it. Just buy new ones if the disks really are your problem. My brake disks always crack out from hole to hole way before they become too thin. You really have to keep those holes cleared, they have a purpose.

Steve in FL

You really don't want to use the standard brake machining process on Porsche rotors. The process I've heard recommended is "Blanchard grinding" (sp?) but as 993_996_enthusiast comments I'd usually just buy new rotors. Although the reported $700+ price per rotor for the iron GT3 front rotors would make me want to find an aftermarket source real fast.

Bob Rouleau

One more vote for clean out the vent holes. I would also replace the pads. If the vent holes are plugged, you have probably also overheated the pads. When the pads exceed their temperature limits all sorts of weird things happen. If you remove them you will probably see large craks and an uneven surface. It isn't hard to look - pluuing the pads is 5 minutes per wheel. My suggestion, clean out the vent holes, you may have to use a drill bit to do this. It is a tedious job. If you are lucky, compressed iar blasts may work. While you have the wheel off, pull the pads and examine them. I bet you find that they are in poor shape. Replace pads, bed carefully and you should be just fine.

I'm with macfly on the Pagid blue - a nie all round pad. The Pagid Orange are too cold blooded for the street and very noisy when cold.

When you wash you car, always drive it and heat up the brakes to avoid rust. This applies to PCCB as well to my personal big surprise! There has to be some metal in that composite or, its iron (carbon) from the pads themselves but I rusted my pads solid.

Karl S

I'd also suggest that you avoid blowing out the holes with compressed air unless you are wearing proper eye and nose protection. I did this once at the track and it resulted in my tear ducts getting plugged. That resulted in large bumps on my eyelids and under the eyes, which took many weeks to go away. That flying brake dust can do nasty things to you. It's much safer to use a drill bit or screw driver to clean out the holes.

Karl

JakeMate

More great advice from everyone. Thanks.

I will definitely clean out the vent holes first. I might then try some garnet paper as Stoptech suggests. Pretty inexpensive things to try, so it's probably worth it. Blanchard grinding would be next if that doesn't work. Would rather not pay for new rotors yet if there is a cheaper and effective solution.

Does anyone know where to get garnet paper?

Also, who will blanchard grind rotors? Turning is pretty common but I don't think blanchard grinding is. I wonder of you need any special fixturing. My buddy has a machine shop and might have a blanchard grinder. Maybe I'll ask him.

JakeMate

Update:

I found some garnet paper (as Stoptech suggests) at Ace Hardware.

I took the front rotors off tonight and tried the sand paper. It barely touched it. It looks like that pad deposition is in there pretty good. I mic'd the rotors recently and they're right in the middle of the range.

I think I'll take the rotors over to my mechanic tomorrow and have him look at them. I really don't see a problem with machining the rotors as long as they're above the minimum thickness specification. Why would Porsche use the verbage 'machined' and specify the numbers below if it weren't OK to turn them?

New 28
Minimum Machined 26.6
Minimum 26

enthusiast

The problem with machining them is getting the brake disk mounted correctly so that it is 'true' with respect to lateral run out.

JakeMate

I guess that's a problem with any rotor. The setup looks like it would keep the machined surface parallel with the rotor mounting surface very accurately. I didn't really see a problem with it.

Anyways, I had them turned today. They're still a fair amount above the minimum machined thickness. My mechanic only needed to take about .004" per side to remove the brake pad deposition. I just finished mounting them up and I took it for a spin. It felt good so far, but I really need to bed them in and test at high speed to see if the problem has gone away.