mesa87

I got a tip from a fellow driver while at Sebring. My front rotors are toast and he advised that he uses 928 GTS rotors for his big reds (fronts). After some searching I found that the 928S4 rotors are dimensionally the same but solid, not drilled nor slotted.

Anyone ever done this before? My guy also sends his rotors to a machine shop to have them slotted...seems like a good idea.

Seems like the rear rotors are a different story, can't seem to find solid ones that are OEM (not Zimmerman)

Any experience or opinions with this?

Per usual, thanks for the help!

Garth S

928 S4 fronts are 305x32mm vs. those of the GTS at 322x32mm .... which is also the TT/C4S dimension; however, the S4 mounting face to rotor centerline offset is +5mm greater than that of the 993 322mm rotor.

mesa87

Thanks Garth,

My car has the regular 993 brakes, do you know if the offsets for the S4 rotors will work? My friend did not mention havng any trouble with the offset for his Big Reds, but I'll ask to be sure.

Thanks,

FLA997

If they match up for the C2, this would be very nice for those that track their cars and are sick of cracking drilled rotors in short order. I'm sure someone knows the answer...

Garth S

With 'a grain of salt' qualifier , I do not think so. I do not have a std. 993 front for comparison, but do know that 928 S4 brake conversion kits for earlier 16v 928's use std. 993 front rotors .... presumably in that they have a different offset than the more readily available ( to a 928 owner) S4 rotors.

Perhaps PM Cobalt ( Anthony), for he has a treasure trove of caliper & rotor data.

mesa87

Garth, as a newbie and recent 993 owner I cannot in good faith make any absolute assesments on what will and will not work .

I know that I'm tired of cracking rotors (2 this season) and needed a better solution. For $100 a wack it seems like it's worth a shot, should it not work I'm no worse off than I was before and if it does work it may provide a simple solution to other drivers who experience the same problem.

I based my findinds on this link that was provided some time ago.

http://members.rennlist.com/1976c38/brakes.htm

Hope this helps...

ed devinney

I've got S4 brakes on my 951S and as Garth says the offset is different. Have the rotors off the 951 and my old 993 rotors in the barn, let me know what measurements you want.

Garth S

I understand the $problem$ As good as that reference is, I didn't see any rotor offset data. Where they refer to S4, I think it is pad type being indicated.
Front calipers are radial mount, so the offset required to center the rotor is pretty much a given ( rears, having axial mounts, can be moved inboard with spacers).
Anyway, it is all a bit academic until the measuring tape comes out I do have front S4 and C4S rotors here, so if I can help with any measures ... let me know.

Bill Verburg

The page referenced above is mine and no, there is no rotor o/s data there.

w/ stock uprights and hubs the 964 and 993 base rotors are not interchangeable, the 964 can use the 928S4 304x32 one piece rotor w/ a caliper adapter and 993 front calipers(993 fronts are essentially the same as 928S4 calipers when the bleeds and feeds are swapped). The caliper adapter takes care of any rotor o/s issues.

Never measured a 928GTS 322x32 one piece rotor.

If you want to check rotor o/s's measure from the back of the mounting face to the back friction face. A stock 993 rotor is ~66mm

mesa87

So, in short...the standard S4 rotors will not work with regular 993 calipers without modification? Sorry to beat a dead horse but I can still get the regular rotors (drilled) and spare myself the pain.

Thanks guys, I appreciate the help.

Garth S

... and it is 71mm by the same criteria on a S4 front .... same +5mm as measured from the 322mm 993 rotor noted in post #2: close, but no cigar

Bill Verburg

You could always use this rotor


and have a hat w/ the correct o/s made for you

a floating hat will reduce thermally induced stress cracking, upgrading to 993RS/tt spec also keeps temps down and thus longevity up

mesa87

Thanks guys for the valuable information...it was worth a shot!