What should the brakes feel like?
Discussion
Got the 964's brakes pretty much completely replaced last November - new front disks, pads, caliper strip and clean - by local Leeds specialist. Prior to the swap I had noticed a fairly pronounced judder under moderate braking so I was not surprised when the mechanics told me I needed them doing.
However, five months and a few spirited drives later, I notice that the judder is still there (also, they now squeal like a 1970's Routemaster, but that's another story). Given the 911's peculiar layout and lack of weight over the front wheels, should I expect a bit of a tremor through the wheels under hard braking? Or, should they be rock solid (esp having been replaced)?
However, five months and a few spirited drives later, I notice that the judder is still there (also, they now squeal like a 1970's Routemaster, but that's another story). Given the 911's peculiar layout and lack of weight over the front wheels, should I expect a bit of a tremor through the wheels under hard braking? Or, should they be rock solid (esp having been replaced)?
Should be solid, mine are.
I would guess you may have some pad residue if they judder....take it for a blast, and then apply the brakes heavily several times to remove any pad build up, or use some sand paper/wet&dry to remove any from the disks..
There was a thread around here recently that explained one way of bedding new pads and disks in, it looked pretty effective to me.
Kevin.
I would guess you may have some pad residue if they judder....take it for a blast, and then apply the brakes heavily several times to remove any pad build up, or use some sand paper/wet&dry to remove any from the disks..
There was a thread around here recently that explained one way of bedding new pads and disks in, it looked pretty effective to me.
Kevin.
From here www.stoptech.com/ under "Tecnical Information FAQ"
What do you mean by "uneven pad deposition?"
Virtually all modern brake pads are what are referred to as an Adherent type of pad. The pad is designed to transfer a layer of pad material onto the rotor. When a sufficient and EVEN layer of pad material is adhered to the rotor face, the pad material on the rotor, interacting with the similar material on the pad, creates the most efficient friction mechanism. These like materials, breaking against each other on a molecular level are what really stops the car well. To emphasize, there is supposed to be a layer of material pad material on the rotor. The problems occur if the pads are not properly bedded-in (an even layer of pad material on the rotor) and run aggressively, OR if the pads are overheated (street pads on the track like we tell 37 people a week NOT to do). The pad transfer occurs most efficiently at the pads optimal operating temperature. That means a higher temperature pad needs to be hotter to properly transfer material. If you have a high performance pad and never run it hot enough to get a proper layer of material onto the rotor, it will never be properly bedded-in. Thus, even after 1000 miles of "normal" street driving, when you blast your favorite canyon and heat the brakes, you can get uneven deposits on the rotor causing a vibration. The other common scenario is over-heating the pads even if they are properly bedded-in. In this case, the pad material starts to break down and smear onto the rotor face, again causing the UN-EVEN deposits. The other problem that occurs is if the system is really hot and you come to a complete stop and leave your foot on the brake pedal. In this instance, we get what is called "pad imprinting" where a small layer of material breaks off the surface of the pad and literally can be seen as an imprint of the pad on the rotor face. This can occur no matter the state of bed-in. All these scenarios leave very small, uneven layers (we call it TV, Thickness Variation) of material on the rotor. We're talking a few 10/1000's of an inch, like a TV of 0.0003". It starts out almost imperceptibly, but as the pads start to skip over the high spots, more material is deposited on those areas, ever increasing the vibration until it becomes quite noticeable, even days after the event that started it occurred. The best way to avoid these problems is proper bed-in of the system initially, and using the proper pads for your exact driving conditions. If you are planning on swapping pads for a track day, you need to re-bed the system before the event (or dedicate the first track session to bed-in). Remember, you have that layer of street pad material adhered to the rotor face, and if you don't remove and replace it with the track pad material, it is going to degrade from the heat and... yep, cause uneven pad deposits. Same goes when you put the street pads back in, you need to re-bed them for optimal street performance. The article on the Technical page titled "The Warped Brake Disc and Other Myths of the Braking System" is an excellent source of information:
www.stoptech.com/tech_info/wp_warped_brakedisk.shtml
My car judders when I apply the brakes, what can I do to fix it?
In order to understand the likely cause of the judder, please see the FAQ relating to un-even pad deposition. OK, now that you hopefully better understand why the steering wheel is shaking out of your hand, what can be done to cure it? Turning the rotors will take care of it, but you will be shortening the life of the rotor and decreasing its ability to absorb and control heat, as there will be less mass in the rotor after turning. Also, turning a 2-piece rotor that uses floating attachment hardware between the rotor and hat can be tricky. We have had very good success running an aggressive track pad at lower temperatures on the street in order to scrub off the rotor surface. We have found the Hawk Blue 9012 race pad to be very effective. At lower temperatures it is very ABRASIVE, not becoming ADHERENT until it reaches it's optimal operating temperature. If it is used with a few firm stops at a time, not getting too hot (we want to remove material, not transfer more), it will often remove the source of vibration. A WARNING: Do not leave an abrasive pad in the caliper longer than necessary to solve the problem. We have had rotors destroyed in under a week by leaving the abrasive track pads in on the street.
What do you mean by "uneven pad deposition?"
Virtually all modern brake pads are what are referred to as an Adherent type of pad. The pad is designed to transfer a layer of pad material onto the rotor. When a sufficient and EVEN layer of pad material is adhered to the rotor face, the pad material on the rotor, interacting with the similar material on the pad, creates the most efficient friction mechanism. These like materials, breaking against each other on a molecular level are what really stops the car well. To emphasize, there is supposed to be a layer of material pad material on the rotor. The problems occur if the pads are not properly bedded-in (an even layer of pad material on the rotor) and run aggressively, OR if the pads are overheated (street pads on the track like we tell 37 people a week NOT to do). The pad transfer occurs most efficiently at the pads optimal operating temperature. That means a higher temperature pad needs to be hotter to properly transfer material. If you have a high performance pad and never run it hot enough to get a proper layer of material onto the rotor, it will never be properly bedded-in. Thus, even after 1000 miles of "normal" street driving, when you blast your favorite canyon and heat the brakes, you can get uneven deposits on the rotor causing a vibration. The other common scenario is over-heating the pads even if they are properly bedded-in. In this case, the pad material starts to break down and smear onto the rotor face, again causing the UN-EVEN deposits. The other problem that occurs is if the system is really hot and you come to a complete stop and leave your foot on the brake pedal. In this instance, we get what is called "pad imprinting" where a small layer of material breaks off the surface of the pad and literally can be seen as an imprint of the pad on the rotor face. This can occur no matter the state of bed-in. All these scenarios leave very small, uneven layers (we call it TV, Thickness Variation) of material on the rotor. We're talking a few 10/1000's of an inch, like a TV of 0.0003". It starts out almost imperceptibly, but as the pads start to skip over the high spots, more material is deposited on those areas, ever increasing the vibration until it becomes quite noticeable, even days after the event that started it occurred. The best way to avoid these problems is proper bed-in of the system initially, and using the proper pads for your exact driving conditions. If you are planning on swapping pads for a track day, you need to re-bed the system before the event (or dedicate the first track session to bed-in). Remember, you have that layer of street pad material adhered to the rotor face, and if you don't remove and replace it with the track pad material, it is going to degrade from the heat and... yep, cause uneven pad deposits. Same goes when you put the street pads back in, you need to re-bed them for optimal street performance. The article on the Technical page titled "The Warped Brake Disc and Other Myths of the Braking System" is an excellent source of information:
www.stoptech.com/tech_info/wp_warped_brakedisk.shtml
My car judders when I apply the brakes, what can I do to fix it?
In order to understand the likely cause of the judder, please see the FAQ relating to un-even pad deposition. OK, now that you hopefully better understand why the steering wheel is shaking out of your hand, what can be done to cure it? Turning the rotors will take care of it, but you will be shortening the life of the rotor and decreasing its ability to absorb and control heat, as there will be less mass in the rotor after turning. Also, turning a 2-piece rotor that uses floating attachment hardware between the rotor and hat can be tricky. We have had very good success running an aggressive track pad at lower temperatures on the street in order to scrub off the rotor surface. We have found the Hawk Blue 9012 race pad to be very effective. At lower temperatures it is very ABRASIVE, not becoming ADHERENT until it reaches it's optimal operating temperature. If it is used with a few firm stops at a time, not getting too hot (we want to remove material, not transfer more), it will often remove the source of vibration. A WARNING: Do not leave an abrasive pad in the caliper longer than necessary to solve the problem. We have had rotors destroyed in under a week by leaving the abrasive track pads in on the street.
Only one thing to add to slippy's comprehensive post. If they are genuine porsche discs and pads then you should not have a problem. Except we used to champher the leading edge of the pad to stop the pads squealing. My 965 3.6 used to warp the front discs which transpired to be a caliper problem. New front calipers fitted, problem solved.
bumcrack said:
If it's the "local Leeds specialist" that starts with a S, I'm not surprised. There trick is to say you need new disks, even when you've just had you car inspectied by JCT in Leeds and it's been given a clean bill of health alround.
In my case it was completely the other way around.
JCT told me I need to replace them and Strasse advised this was not necessary and just stripped them down and cleaned them up.
Gassing Station | Porsche General | Top of Page | What's New | My Stuff