Help needed to identify brakes on racecar

[Cory M]

One for the Porsche brake experts (KTL? Bill V? )

These brakes are adapted to a 914 GT racecar. I haven't taken any measurements yet but they fit under 16" wheels. Previous owner referred to them as "big reds", but they are different than the 993 Turbo/RS brakes that are typically called big reds. They aren't 930 brakes either. Are they 944 Turbo brakes? 964? I need to replace the front rotors now and eventually pads. First 2 pictures are front, last one is rear.

Can anyone identify them? Or tell me what I need to check to verify?

Thanks!

[Bill Verburg]

Originally Posted by Cory M

One for the Porsche brake experts (KTL? Bill V? )

These brakes are adapted to a 914 GT racecar. I haven't taken any measurements yet but they fit under 16" wheels. Previous owner referred to them as "big reds", but they are different than the 993 Turbo/RS brakes that are typically called big reds. They aren't 930 brakes either. Are they 944 Turbo brakes? 964? I need to replace the front rotors now and eventually pads. First 2 pictures are front, last one is rear.

Can anyone identify them? Or tell me what I need to check to verify?

Thanks!

The fronts appear to be 993 or 928S4 painted red, Is that a 32x304mm rotor?
the rears are indeterminate, obviously a small 2 piece Brembo, but there were several versions that varies by piston size and throat width for 24mm or 28mm rotors. It looks to be on a 3.2 Carrera 24mm rear rotor

[Dan J]

I think you'll find that those are 86 944 turbo frt rotors. I think Bill is right about the rears

[group911@aol.co]

Front rotors appear to be turbo as they are using late 930 hubs. Are the front calipers radially mounted?
Rear rotors look like maybe a 964 front??? as the don't have the holes that you would screw to the hubs. I also can't see a hub flange coming through on them.
Notice on both ends how little of the surface area is actually getting used?

[Cory M]

Thanks for the info.

I didn't get a great measurement on the diameter but it appears to be 304mm for both front and rear ( could be slightly less or more, just eyeballing it with a tape measure). Front rotors are 32mm and the rears are 28mm. On the front the offset from the hub mounting face to the face of the disk is about 26mm, on the rear it's about 55mm. Both the front and rear calipers are mount radially and are using adapters. The bolt spacing is 130mm for both.

Could be 944 turbo calipers on 930 rotors...

[Bill Verburg]

This rotor is almost certainly an '81 up 930 front


Here is an unmounted one 32x304 note the unusual hole pattern


The only 28mm rears were
930 @309x28
965 @299x28
993RS/tt @322x32

the 28mm fronts were
964 @ 298x28
944t, 944S2,968, 968CS @299x28 these are 17mm from the rotor face to the mounting face for <'86 and 46mm >'86

[Bill Verburg]

The 930 rear is 55mm from the rotor face to the mounting face and is 28x309

[Cory M]

Great. Thanks for the specs. I'll get some front rotors ordered. I think the rear rotor is most likely a 930 too. The wear pattern leaves about 5mm of the edge untouched and with most of these rear calipers designed for a 299mm rotor it makes sense that you'd have 5mm unused on the radius of a 309mm rotor. The rears are in good shape so no need to replace them yet.

[KTL]

This front caliper tends to create a lot of uncertainty. It originated on the 928 S4 (and the 959) and then appeared on the 944 Turbo with the optional M030 setup, which eventually became standard on the 944 Turbo S. They use the 304mm rotor. The early S4 calipers have 42/26 pistons and then eventually they all were made 44/36.

Along comes the 964 Turbo & 928 GTS and the confusion really begins when the slightly larger "big red" calipers appear, which were also black, and used a larger 322mm diameter rotor. The 993 comes along and uses the smaller S4 caliper with the 304mm rotor and the 993 twin turbo uses the larger big red with the 322mm rotor for more confusion. I'm sure there's some other Porsche model nuances i'm missing......

The S4 size front calipers can definitely fit under 16 inch wheels. I had those S4 front calipers fit nicely under both the BBS RS 3-piece street wheels, as well as under the more vanilla BBS one piece wheels. The only 16 inch Fuchs i've seen them fit under is either with spacers or the three Fuchs wheels that have deep hubs for brake clearance- 944T 16x7, 944T 16x8, 930 16x9

That rust line on the rear rotor OD is odd because it's hard for me to think that the top of the pad is below the OD of the rotor. In that case the rotor OD usually wants to hit the "roof" of the caliper. Often we see the reverse situation where the caliper isn't sitting down far enough on a smaller diameter rotor and that puts the top of the brake pad above the rotor OD, leaving you with a sliver of untouched brake pad around the top.

On the typical 911 pre-964 aluminum trailing arms we're familiar with, I have found an unlikely rotor that can be used in lieu of the 930 rotor is the 299x28mm 964 FRONT rotor. The hat ID is a perfect fit to the older 911 axle hub OD and therefore registers perfectly. The hat offset is very close to that of the 930 rear rotor. 930 rear is 80mm from top of hat to far side of rotor face and the 964 front rotor is 83mm hat to far face Only caveat is that you have to ditch the entire parking brake assembly and lop off a piece of the trailing arm that serves the parking brake cable route.

So my point is that if the 930 rear rotor is what's currently on there, you may want to test fit a 964 front to see what that does for you. That is, assuming you don't have any issues with parking brake back there since it's a racecar? The 964 front is not as elegant as the 930 that has directional cooling and drilled/cast holes. But it's a beefy SOB and can certainly handle the abuse of racing. One could argue it's a bit more durable than the 930 since it doesn't have the holes in it which tend to promote cracking? 930 rotor is a great rotor nonetheless. We've used them for years with no problems.