mkozink

Good news- they fit! There has been so much speculation about this retrofit that I hope this helps close the information gap.

Everything went together nicely; the back fit perfectly and the front only needed some minor spacing to compensate for the difference in pad position on the rotor (between 2-3mm).

Front 997.2 GT3/RS 380mm steel rotor test fit on 997.1 GT3RS PCCB calipers with 18" CCW C10 wheels and Toyo R888 tires



Rear 997.2 GT3/RS 350mm steel rotor test fit as above



Tech forgot to weigh before install. I am picking the car up Wednesday evening/Thursday morning so I hope to post part numbers, etc, at that time.

I am participating in the Northern Ohio Region BMW CCA Memorial Day HPDE at Mid Ohio, May 28-30, so I should have some reasonable on track experience to report.

sws1

What was involved in adjusting the spacing?

P.J.S.

how much do they cost?

Carrera GT

I don't see the point in going to the factory drilled rotors -- they holes make them crack and groove. Why not go with a slotted rotor?

mikymu

Thanks for the post and glad to see they fit!

What kind of spacer did your tech use? They forgot to weight the rotors!? Get you money back lol

Carrera GT

The "spacers" are a bit of a worry unless done properly. Even a 2mm shim warrants a 5mm longer caliper bolt or a stud insert. Hopefully the absent minded tech that ignores the work order (assuming "weigh rotors" was on the work order) also used new bolts and cleaned the threads in the calipers.

Larry Cable

cheaper/availability I think...

Larry Cable

not sure if the spacer is on the caliper or on the pad itself ...

cfjan

I'm guessing the spacer has to be on the rotor.. because the calipers are mounted radially.. it can only move out to accommodate larger diameter rotor, but not side to side..

TRAKCAR

So does that mean that the rear steel rotors are interchangable between rear steel MKI and MKII?

Larry Cable

PCCB yes, not sure about rears, but as I recall I think the rear caliper mountings are "identical"...

Carrera GT

This excerpt from the original post, "difference in pad position on the rotor" suggests to me pad location, not rotor alignment in the caliper between the pads. And again, if you put a 3mm spacer behind the rotor -- between the rotor and the face of the axle flange -- you'd still need the rotor centered between the sides of the caliper, so that's a compensate for the rotor hat, not the pads.

For what it's worth, a radial caliper mount is a different concept, but I know what you mean: the caliper is axial. I think the rotor hat is larger, making it necessary to move the caliper away from the center axle line so the pads clear the hat and sit in the intended swept area of the rotor, so the installer put some sort of machined shim spacer between the caliper and the wheel carrier. This is not something I'd expect a dealer to do unless they had factory parts and an approved fitment service bulletin. It seems to me we can conclude that there is some minor difference between the 2010 steel GT3 and ceramic brakes. Since they use the same pad part number, there's still a mystery. maybe the caliper is different (just machined with a different offset) or the wheel carrier is different (which would seem like a bad product decision, but you never know.)

Perhaps someone can just put a steel rotor on a table next to a ceramic rotor, lay a straight edge across the hats and across the rotors -- anything offset or thickness differences will be apparent. Then lay the rotors fact to face and any diameter differences will be equally apparent.

cfjan

I guess only OP can comment then.. I was thinking that it should NOT need any shim on the caliper bolt to move it out to clear the hat, as both rotors are of the same size.. if you have to move the caliper out, that would mean some part of the pads are not being used on the outer edge.. (or in the original configuration that the pads are not touching the outer most portion of the rotor, which I don't think would be the case).

Would be interesting to hear, though.. !

mkozink

Thanks for everyone's interest in this retrofit.

As both cfjan and Carrera GT deduced from my original post the rotor fits over the hub just fine. No issues with spacing or offset. The 997.2 GT3/RS steel front rotors are dimensionally identical to the 997.1 PCCB rotors in how they fit over the hub and align laterally (using the plane of the axle as the z axis) in the caliper.

The difference is the alignment in the horizontal, front to rear, or x axis of the caliper brake pad surface. The PCCB rotor is a true 2 piece design (consumable CC friction ring mounted to a reusable aluminum hat) while the 997.2 GT3/RS steel rotor is a one piece construction (steel friction ring wedded to an aluminum non reusable hat- see below).



The alignment issue is a result of the void between the hat and the friction ring in the 997.2 GT3/RS steel rotor. With out shimming the caliper ~2.5mm away from this void the anterior (inner) brake pad surface would impinge in this area (apparently there is a Porsche service bulletin about this) while the posterior (outer) brake pad surface would be too far from the outside edge of the friction ring. Shimming out the caliper properly aligns the brake pad surface and friction ring for optimal performance.

I am not certain why the void between the friction ring and hat section exists. If I guessed it would be a function of weight savings and cooling efficiency. What ever the reason for the void it makes the alignment of the brake pad and friction ring more critical for the 997.2 GT3/RS steel rotor than for the 997.1 GT3/RS PCCB rotor (PCCB rotor has more friction ring surface area than the 997.2 GT3/RS steel rotor due mainly to this void). When I have a chance I will measure the 997.1 PCCB take off rotors and compare to 997.2 steel.

BTW- some people have requested part numbers for the 997.2 GT3/RS steel rotors. They are listed below;

P997-351-409-91 (left front)
P997-351-410-91 (right front)
P997-352-405-92 (rear; not certain if left or right)
P997-352-406-92 (rear; not certain if left or right)

My cost was $504.90 each for the fronts and $489.16 per rear (total $1988.12).

cfjan

Thanks for the info! In this case, I wonder why wouldn't the factory move out the caliper 2.5mm (like what you did) on the PCCB rotor, since it would seem to be more ideal (grabbing the outer friction surface, effectively equivalent of 5mm larger disc). Hmm...