964 Turbo Front rotors ignorance

[GAJ]

Can anyone tell me if the 964 turbo 3.3 91-92 and the turbo 3.6 93 front rotors are interchangeable? can I fit the newer rotors to my 1992 3.3? both are 322x32 in size but can't find any reference on the hat sizes.

Thanks for the help.

[911nut]

No they are not.
The '91-93 caliper and pad are somewhat smaller than the Turbo 3.6 set-up. All have the same size pistons but the 3.6 caliper and pad are 10 mm taller.
You can use the Turbo 3.6 rotor on the '91-93 but if you go to the 928 GTS caliper that got used on the 3.6 you'll have 10 mm of brake pad hanging off of the smaller rotor.

[GAJ]

Thank you!!! you save me! almost buy the wrong ones.

[TurboKraft]

Sorry, that's not completely correct.

The rotors are 100% interchangable. They have the same OD, thickness, and rotor hat offset. The only visual difference is the 3.6T rotors have a little more cooling fin in the middle, almost like a dividing fin in the same plane as the rotor surfaces.

You are correct about the pads, however. The C2T (S4) pad is the same length as the 3.6T/993T/GTS pads, only not as tall.

[911nut]

Originally Posted by TurboKraft

Sorry, that's not completely correct.

The rotors are 100% interchangable. They have the same OD, thickness, and rotor hat offset. The only visual difference is the 3.6T rotors have a little more cooling fin in the middle, almost like a dividing fin in the same plane as the rotor surfaces.

You are correct about the pads, however. The C2T (S4) pad is the same length as the 3.6T/993T/GTS pads, only not as tall.

I disagree.
You have to lay the rotors side by side to see the difference. The 3.6 rotor braking surface is 10 mm deeper, toward the hat section. Other than that, yes they are the same diameter, thickness and offset.
The quick way to identify the 3.3 vs the 3.6 rotor is the hole pattern on the brake surface; the 3.3 rotor has an alternating 4 hole, 3 hole pattern while the 3.6 rotor has an alternating 5 hole, 4 hole pattern.
The 3.6 rotor can be used with the 3.3 caliper and pad but if someone wants to convert to the 3.6 caliper and pads, the 10 mm of pad depth toward the hat section will hang off the braking surface of the rotor which defeats the purpose of the bigger caliper.
But don't take my word for it, ask Bill Verburg.

[911nut]

Bill talks a little about this here: http://forums.pelicanparts.com/porsche-964-993-technical-forum/370105-964rs-brakes.html

[TurboKraft]

Now I see what you're talking about: the height of the friction surface. Hadn't noticed that before, but yes, the friction surface of the 1994 3.6T rotor is taller than on the 1991-92 C2T rotor.



Hadn't noticed the different C/D pattern, either, but it makes sense that as the friction surface is taller another row of holes was added, too.

Good to know -- thanks!

So the C2T can use the 3.6T rotors, but not the other way around as the lower section of the 3.6 pad would hang off the friction surface.
(Not that a 3.6T owner would want to -- the C2T rotors are more expensive.)

[slyguy]

fivehole...

[GAJ]

wow!! the only sure thing about this car is that I will never stop learning about her! thanks to all for the help!