BC

On Which year? You can use GTS rotors on the big brake calipers if you wanted to. But people do the two piece 993TT rotors at 322mm in diameter.

Anybody else have aftermarket hats? I have two myself, and did this design to make more for my other car.

I'll try and get all the suspension stuff out and mock something up to see the spacing.

heinrich

Brendan that is the point. DR needs to chime in here BUT:

I read through the archives.
Till '86.5 you need pre-'81 spindles + adapters + 993tt rotors for both Big Reds and S4 calipers
After '86.5 you need only the GTS or 993 rotors and Big Red calipers.

BC

That is an extermely good question and bears investigation. Of course Devek is nowhere to be seen (and with my front Konis I sent them last April, who knows - are they out of business?), and even if Marc was here, he wouldn't give a straight answer.

On later cars, when you get the bigger brakes, you simply put them on the original late hubs. And then you have some choices for rotors. On early cars, you need an adaptor to put the bigger rotors on.

BC

That is all correct.

heinrich

And those rotors come with hats

BC

I haven't figured the different offset out yet, or why one would need it.

cobalt

OK back it up a few steps.

To begin with 6061 non heat treated is a dangerous proposition. You will need to use solution and artifical age treated billet to T6 condition for strength otherwise you may be inviting a serious law suit. There is no way I would trust non heat treated aluminum for this application and the tensile strength of T6 condition 6061 is very strong.

Second the GTS rotors are the same as the 94 3.6turbos (single turbo not TT) It is a single piece rotor cast hole vs a solid vented rotor used on the GTS. They are both 322 mm x 32 mm rotors. So are the 993TT rotors 322mm x 32 mm. The difference between the 94 turbo and 993TT are the 993TT rotors are 2 piece with steal hats bolted to the rotor vs 1 piece. The RS/RSR applications used the same rotor with aluminum hats and are expensive although they do save about 4 pounds per corner. The only other difference between the 94 turbo/GTS and 993TT rotor is the offset. If you are using GTS brakes you will need to use the GTS or 94 turbo rotors. Be sure they are 94 turbo and not 91-92 964 turbo rotors as these are different. If you use the 993TT rotors you will need to adjust the adapter for the big brakes to accomodate the different offset used on the 993TT rotor. Since you will be machining hats for these rotors you can use the stock big reds or big blacks and stock GTS/94 turbo offset with the 993TT disk.


I hope this clears things up.

BC

There seems to be alot of confusing here then. Dr sells the 993TT rotors, as H has stated and I see on thier site. These come stock, with the 1.5 inch or so hat that I can see. They do sell adaptors, but for the early cars to use The GTS sized brakes.

You are now saying that the offset IS different between what the GTS rotor/GTS Caliper would be on an S4+ hub and carrier, and what we would see with a GTS Caliper/993TT rotor on an S4+ hub and carrier?

This would seem in direct disagreement with what has been previously written here - in that the 993TT rotors (2 piece) can be used with the GTS sized brakes as is on a late car, and with the mounting brakets on an early car.

Can anyone else shed some more light on this?

heinrich

ACK ... DR ..... where are you?????????

cobalt

I may stand corrected concerning S4+ hub, however I was commenting on this comment.

What I was trying to point out was that the offset of the 94 turbo/GTS rotor is different than the 993TT. So you can't use either the GTS or 993 TT rotor. In your application the GTS rotor apparently will not work if you need the 1.5 inch offset the 94 turbo/GTS rotor has closer to a 2.5" offset (don't hold me to the exact dimension). In both cases they are the same sized disc with a different offset. The 993TT rotor will not work on the GTS or the 94 turbo.





Join Date: Dec 2001
Location: SoCal
Posts: 4,434

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heinrich

I have:
Big Red calipers ** with TwinTurbo/C4S (1995-98) rotors and hats for my S4

and


S4 calipers ** with twinTurbo/C4S (1995-98) rotors and hats for my '85 (plus adapters and 80 spindles).

Are we saying the S4 calipers will work, but the Big Reds won't?

cobalt

I do not know the differences in the spindles between the S4 and GTS offhand. If the offset required is 1.5"'s than the TT rotors should work with the big reds. If it is greater or similar to the GTS and 94 turbo than you will have problems. I am under the impression you need to purchase adapters to use the calipers. So long as your offsets match you should be OK.

heinrich

Thanks for your help Anthony

cobalt

So long as I helped.

BC

I'm more confused now then when I started.

The front Steering knuckle and actual hub are the same part numbers for 89+ and GTS. So there should be no offset difference THERE, with respect to how the rotor would NEED to sit on the hub and knuckle mounting points.