SharkSkin

Greg, it sounds like you're saying that there is no safe way to put S4 rotors on the early spindles(specifically on my '78)? Or that a spacer or 993TT rotor would be required? How much different would the offset have to be for it to clear properly? It seems that the part sold by 928 Specialists(& others) could be easily redesigned with a different offset:

GregBBRD

Yes, it is easy to fix. But why don't they know it hits and quit selling stuff that doesn't work to people that assume the stuff has been looked at and works.....that's my point. Why try to hurt people? Surely I'm not the only guy with eye ***** that can see the ball joint crashing into the rotor....surely they know this happens. Why keep selling crap.....is it really just all about profit?

greg brown

Vilhuer

Which rotor types are used with these adapters? 993 351 045 10/ 046 10 obviously but are those only ones?

Isn't usable brake rotor types determined by position of brake caliper anyway? As long as adapter stays in same position there will be problems. Unless rotors are thinner than what calipers are meant to be used with. When caliper is moved there is need to find different cheap rotors again.

Moving brakes towards outside obviously gets them closer to wheels. Maybe too close for some common wheel options? Which would require use of spacer. Another can of worms again.

SharkSkin

Looking at 928 Specialist's site, it seems that they are just selling the GTS conversion kits, with 2-piece rotors. Maybe they have determined that this is what works, though the big calipers are $$$.

Your post has me wondering now whether the S4 calipers that I've already purchased can be made to work safely on my '78. I've been waiting for my original rotors to wear to the point that they need replacement before converting, now I'm glad I've waited. IIRC the GTS rotors are a larger diameter and will not work with my S4 calipers.

Greg Gray, are the 993TT rotors the same diameter as GTS rotors, or same as S4 rotors? Do you know what the difference in offset is?

RDS928S

Greg/Dave,

The 928 Specialist brake kit for the pre 86.5 cars calls for:

-993 rotors (non TT type)
-early spindle swap
-caliper adapter brackets
-special caliper bolt kit
-GT.GTS.Big Red or S4 calipers.

This is what I just installed. I was told it is safe and hundreds of kits have been sold with no issues.

Thanks Rich

Glen McCartney

I upgraded about 1 1/2 years ago on my MY85. I bought the Big Red calipers and front rotors from a 993 racer. I used the 928Intl adapters which I think are the same as 928Spec adapters. I just went and measured the clearance between the end of the ball joint and the rotor. I have about .110" clearance and there are no marks indicating the rotor has hit the ball joints, and I have driven the car pretty hard, DE at Watkins Glen and bumpy roads of PA and NY.

Is the clearance less than .110" on other installations?

The rears are from an S-4, bolted on with a spacer for correct alignment with rotor and caliper.

The ball joints are stock for MY 85, spindles are from a MY81.

Fabio421

Why couldn't you machine off the minute amount of material needed to make this fit? You are already going from an aluminum ball joint to a steel ball joint right? If so, strength shouldn't be an issue, especially if we are only taling about .110 " . Hell, you could even doo it low tech with a grinder if you wanted.

JEC_31

So what this thread (and the 928 community, especially the 85-86.0 owners) needs is a definite answer to these questions:

A) is the 928 Spec kit (or building your own out of same components like Glen did) going to smack the rotors witht the balljoints, or is there enough clearance?

B) Is this a rotor-and-caliper-bracket placement problem or a spindle problem? In other words, changing which part is the cure?

Chuck Schreiber

I've had mine for 2 1/2 years. Just went to take a look and I can't see any damage to the inside of the front rotors. Anyone else?

SharkSkin

Chuck, which rotors/calipers/adapters do you have?

Garth S

Dave, The 993TT/C4S rotors are 322mm diameter all round, 32mm and 28mm thickness fr/rear respectively. The S4 rotors are 304mm IIRC, same as the standard 993. 993 offsets are different than S4 - suspect that is true for the GTS too, but do not know that as fact.

Greggles

When aligning the front end the lower balljoints are shifted. Does this factor into into the clearence?

Vilhuer

It shouldn't as all relevant parts stay in same position compared to each other.

Chuck Schreiber

Dave,

My whole setup came from Dave Roberts' kit. Adapters, rotors, I'm using S4 calipers.

RDS928S

Chuck,

are your rotors one piece or two piece units?.

Rich