I'm sure this has been asked before but what is the best choice for replacement of the front and rear rotors on my track only 86 951? I use Pagid black pads.

 

I've had much better luck w/ rotors from the dealer than aftermarket Zimmermans. The Zimmermans heat-cracked to the edges while the rotors from the dealer never have.

These are all un-modified (i.e. no drilling or slotting) running PF90 or PF97 pads on stock TurboS.

 

Stock rotors might be the best bet. Drilled Zimmermans and cryo treated slotted rotors both cracked badly.

 

My zimmermans have 4 track days on them with PFC 97's and they look like they have small stress cracks already. Anybody else see this?

Thanks, Mike

 

Yeah, I had Zimmerman's that developed surface cracks real quick. Trouble is, I had just upgraded to S4 brakes on my 951, and attributed the cracks to the possibility that the stock rotor sizes were not up to the added heat.

So, based on this discussion
https://rennlist.com/forums/racing-and-drivers-education-forum/149483-cracking-rotors.html
I upgraded the rotors and tried to change my braking habits.

But I will wonder....
Let us know what you find.

 

Drilled Zimmermans failed with cracks within five track days on the fronts, and maybe seven days on the rears. This was on an 85 911 with stock brake setup.

Slotted rotors cracked to the edge, but not clear on the total service life because they were on the car when I got it at the start of the season. This was the 951 with stock [S] brake setup.

 

I think you will find some cracking on any rotor that you subject to a lot of heat.

I've found the OE rotors don't crack all the way to the edge even when they're getting thin (and I am hard on brakes).

The Zimmerman's I tried developed surface cracks to the edge within several track weekends, so I played it safe and scrapped them.

 

For comparison I have run drilled Zimmermans on my 944-spec car. stock brakes with a 2450 lbs car. I have run these same front rotors for 40+ races. Still look good. Some minor cracking just now starting.

I have gone through something like 4-5 sets of pads ranging from street pads to hawk blues over that time.

I have been very surprises they lasted this long. My guess is the light weight of the car plays a huge role in this.

 

Do most of you guys run plain (non-drilled/non-slotted) OEM rotors? What about cryo'd rotors like www.frozenrotors.com? Are these OEM or Zimmerman?

Max

 

my stock (non-drilled, non-slotted) front rotors were both cracked but not on the braking surface. They actually cracked on the hat (closer to the wheel), radially around the outside. Any idea what caused this?

I've since replaced all the rotors (most likely original too, 110k) with solid rotors and new pads and now have much pedal brake pedal feel, it's not like squeezing a rock anymore.

 

You tellin me that you got 110k miles out of a set of rotors?!? Who cares why they cracked!

 

Squeezing rock? Your calipers were probably struggling to reach the rotor surface. At 110K miles, they could [would?] have been way thinner than minimum spec.

 

pretty sure they were original, i had no receipts for new rotors and i had pretty much everything. they were definitely on the thin side.