Turbo Rotors

[Turbo]

I am replacing my rotors and I wanted to see what others were using and what they thought about their performance. The rotors on the car (89 930) are cross drilled. They performed well. The pedal has a nice linear progression to lock up. All four wheels lock at once resulting in a smooth slide (sometimes I do this for fun ). I was planning on replacing with OEM rotors untill 930fan suggested slotted rotors. My goal is good performance (mostly street but will DE a few times this year) and a reduction in brake dust (I am tired of cleaning the rims every 2 days). Thanks in advance.

Jeff
89 930

[Early_S_Man]

Jeff,

Although there seems to be a great deal of sentiment against the cross-drilled rotors, I have done several sets myself (at home on a drill press at 75 rpm) and never had any cracking problems. The primary incentive for their initial development was to eliminate the wedge-shaped wear pattern of pads that meant more frequent pad changes at Le Mans for 917s. My own car had those wedge-shaped wear patterns on the OEM pads, and cross-drilling DID solve that problem, as well as improving initial wet weather stopping characteristics for the first two seconds after brakes are applied!

Based on my own experiences on three different cars, I suggest replacing your rotors with OEM cross-drilled rotors! I have serious doubts that many of the naysayers have used [what they recommend] since 1984 without having any negative results! I drilled them, and drove the cars ... with no reservations or safety concerns! The factory engineers knew what they were doing when the perforated rotors were fitted to Turbos in production!

[Bill Verburg]

Jeff, your original 930 rotors are 1 piece ventilated and have cast in holes. They were oemd from Brembo, and specificly engineered to have the holes in them. They are the best rotors available in that size for that application.

The concern is when the tiny SC/Carrera rotors are taken to a machine shop where holes are then poked in castings never intended for them, this has been then source of 99% of the cracked rotor stories and accompaning warnings.

[Targa Dude]

Hello Jeff,
I recently installed a set of Brembo cross drilled rotors on my 911S
and I found them to be very responsive, with nice stopping power. I dont race my car anymore so I could not tell you how well they work under race conditions. as for the break dust and cleaning my rims I decided to run PBR Brake pads and I'm very happy with them. no more cleaning every 2 days. now I simply dust them with a clean cotton cloth every week and they look great.

Jorge (Targa Dude)

[pbs911]

I have had the same experiences as Warren and Jorge. No tracking yet, so I can't tell on those grounds. I use Ferrado pads and there is very little brake dust with very good stopping power. I am using the OEM Zimmerman cross-drilled rotors. My rotors are the SC type and much thiner than the 930. I would bet you would have no problems with the 930 cast rotors with holes.

[autobonrun]

Once when I stopped by a Ferrari dealership, I asked a mechanic why some of their brand new high performance cars did not have drilled rotors. He said that the benefit of removing gases was offset by the fact that it's more difficult to get the rotors up to temperature during street driving where the cars spent most of their time. Do you agree that if a car is driven mostly on the street, cross drilled rotors could hurt performance?

[ChrisBennet]

Originally posted by Bill Verburg
Jeff, your original 930 rotors are 1 piece ventilated and have cast in holes. They were oemd from Brembo, and specificly engineered to have the holes in them. They are the best rotors available in that size for that application.

The concern is when the tiny SC/Carrera rotors are taken to a machine shop where holes are then poked in castings never intended for them, this has been then source of 99% of the cracked rotor stories and accompaning warnings.

The last 930 rotors I bought were from Zimmerman but I agree with Bill on the drilling SC/Carrera rotors.
-Chris

[Bill Verburg]

Chris, early 930 rotors were Zimmereman, by the end of production they had switched to Brembos. Both are still available.

[930fan]

This is a tricky subject since many people swear one is better than the other so I guess I can only give my 2 cents worth.

My experience with OE cross drilled rotors is that they crack around the holes. Why this happens I don't know. I've only tracked the car a few times and I do a fair amount of high speed stops on the road but I cannot imagine that I am any harder on the brakes than some other track regulars like Bill Verburg and Jack Olsen that don't have this problem but the fact is that I do have cracks on my rotors. Visit any Porsche repair shop and you will also see that this problem is by no means uncommon among 930s, C2 turbos and 993s.

I also know that I did not notice any difference in braking performance (response, fade, noise) in switching to slotted rotors. The slotted ones are lighter though with their aluminium hats and are cheaper to replace since the hats can be reused. The biggest plus for me is that they can't crack around the holes because they have none! I was mighty pissed off when I had minor cracks develop after a few thousand miles on my OE rotors.

Race cars use both types (see Trans-Am, Speedvision GT, ALMS, FIA GT) so again, there is no clear data on which is preferable. Even the respected brake manufacturers (Brembo, AP, Alcon) offer both types on their top kits.

YMMV.

[Turbo]

Thank you all for the input. I was unaware that the factory rotors were cast with holes. I assumed they were either cross drilled or aftermarket rotors. I am still interested in the slotted rotors though. Does anyone else use them? I am also interested in a couple of points that were made in old rotor threads. One is about freezing the rotors for added life and the other is a post that says it is important to cure the rotors with old pads to remove oil and steel stress. Does anyone here actually run frozen rotors? How much does it extend rotor life? Does it change the feel of the brakes? Is it really necessary to cure the rotors to get maximum life out of them?

Jeff
89 930

[Bill Verburg]

My rotors freeze all winter. Never noticed any extra special qualities in them. VCI recommends and sells slotted rotors for your application.

Rotors do need to be clean and grease free, normal cleaning solvents are adequate for the job.

New pads do need to be bedded in and heat cycled, here is Brembos recommendations in this regard;

Any time different friction materials or discs are introduced, a bedding procedure should be carried out.

• While the vehicle is stationary, pump brakes to ensure a firm pedal.
• Drive the vehicle cautiously to test fit and function.
• The brakes should be smooth, with no vibrations, judder, etc.
• Drive the vehicle to a remote area and perform at least 30 brake applications of 3-second duration. Use light/medium deceleration with varying starting speeds. Leave at least ½ mile between each brake application.
• The purpose of this procedure is to gradually increase the temperature in the components without inducing thermal shock, and to mate the brake pad and disc friction surfaces.
• After the repeated stops, drive the vehicle for several miles with little or no braking in order to adequately cool the components.
• After the above process is completed, the system is ready for normal use.
• When the system achieves elevated brake temperatures for the first time, a slight increase in pedal travel and pedal effort may occur. After this first "fade" and proper cooling, the system will maintain its optimum performance at all temperatures.