930 Rear rotor fitment on SC

NoEardGoat · 04-24-2012, 07:00 PM

I am installing a set of 993 front and 965 rear calipers on my 1981 SC. When I removed the rear rotor it was a tight fit between the hub and the rotor ID. It takes some effort and jiggling to get it loose. This is typical of many of the brake rotors I have worked on before.

The 930 rear rotor has a much larger ID than where it fits on the SC's hub. It slides right over, but additionally it doesn't fit real tight on the wheel studs. The only force holding them on the hub will the tiny tapered flat head screws and what ever "pinch" force is created when installing the wheel. Is it OK to run like this???

I read about people just bolting them onto an SC. The SC and 930 show different part #'s for the rear hub. Can anyone confirm a larger ID on the 930 hub where the rotor sits vs the SC?

Steve@Rennsport · 04-25-2012, 12:21 AM

You have the right side rotor installed on the left hub; I'd sure recommend swapping those side-to-side for proper cooling.

Those fit 911 hubs without problems (provided that the dust shield mounting bosses are removed) and you can simply use the same screws to secure the rotors onto the hubs.

Bill Verburg · Bill Verburg's Garage

As Steve says, you might want to paint the hub unless you the rotors you have are zinc coated

NoEardGoat · 04-25-2012, 10:17 AM

Quote:

Originally Posted by Steve@Rennsport

You have the right side rotor installed on the left hub; I'd sure recommend swapping those side-to-side for proper cooling.

Those fit 911 hubs without problems (provided that the dust shield mounting bosses are removed) and you can simply use the same screws to secure the rotors onto the hubs.

Thanks for the keen eye! For test fitting I just grabbed one without paying attention.

Which e brake pads should I use with the 930 rotor, SC or 930?

I removed the SC dust shield as it obviously didnt' fit the larger 930 rotor, but left the plate (mounting boss) it mounts to installed. Does this need to be removed as well?
Do I need to acquire the 930 dust shield parts or just run it without the dust shield?

Thanks for the paint tip, I will probably have it pc'd black with the front hats and some other parts.

Bill Verburg · Bill Verburg's Garage

Quote:

Originally Posted by NoEardGoat

....
Which e brake pads should I use with the 930 rotor, SC or 930?

I removed the SC dust shield as it obviously didnt' fit the larger 930 rotor, but left the plate (mounting boss) it mounts to installed. Does this need to be removed as well?
Do I need to acquire the 930 dust shield parts or just run it without the dust shield?

....

SC & 930 parking brake shoes are the same, use you stock ones.

the boss depends on where the caliper sits, if you haven't had to remove it yet you won't(assuming that the caliper is bolted in place and not just resting there)

KTL · 04-25-2012, 12:24 PM

The hub diameter of the SC and 930 rotor are the same, as are the inside diameters of the rotor hats (not the center bore diameter, but the diameter inside the hat itself)

Keep in mind that rust/corrosion build-up inside the rotor hat affects how tight it fits onto the wheel hub where the hub and rotor come in contact with each other at the OD of the hub and the ID of the rotor hat. This is a precise fit and its what makes the rotor hub-centric.

Also the adjustment of your parking brake shoes affects how the rotor comes off. If the shoes have worn down the parking brake "drum" brake contact area on the rotor hat, a ridge can form at the outer edge of the drum. That ridge makes it difficult to remove the rotor because that ridge can't get past the brake shoes. When that happens, you have to retract the shoes by adjusting the star wheel adjuster to get the rotor off.

You don't need to remove the SC dust shield mounting plate. The 930 rotor will clear it. It's actually part of the parking brake mounting assembly. So you're better off leaving it alone.

NoEardGoat · 04-25-2012, 05:44 PM

Quote:

Originally Posted by KTL

The hub diameter of the SC and 930 rotor are the same, as are the inside diameters of the rotor hats (not the center bore diameter, but the diameter inside the hat itself)

Keep in mind that rust/corrosion build-up inside the rotor hat affects how tight it fits onto the wheel hub where the hub and rotor come in contact with each other at the OD of the hub and the ID of the rotor hat. This is a precise fit and its what makes the rotor hub-centric.

Also the adjustment of your parking brake shoes affects how the rotor comes off. If the shoes have worn down the parking brake "drum" brake contact area on the rotor hat, a ridge can form at the outer edge of the drum. That ridge makes it difficult to remove the rotor because that ridge can't get past the brake shoes. When that happens, you have to retract the shoes by adjusting the star wheel adjuster to get the rotor off.

You don't need to remove the SC dust shield mounting plate. The 930 rotor will clear it. It's actually part of the parking brake mounting assembly. So you're better off leaving it alone.

Thanks for the explanation I understand the fitment much better now.

Should I bother with getting 930 dust shields or just run the rotors without?

Bill Verburg · Bill Verburg's Garage

Quote:

Originally Posted by NoEardGoat

Thanks for the explanation I understand the fitment much better now.

Should I bother with getting 930 dust shields or just run the rotors without?

w/o

KTL · 04-26-2012, 06:39 AM

Bill's picture tells the fitment story perfectly. See how the inner shield fits very closely within the parking brake drum? That's because the drum/hat dimensions are the same for the SC, Carrera, 930 rear rotors.

You actually cannot install the splash shields for the 930 rears. The 930 rear caliper is mounted in a different location on the 930-specific trailing arm. So the shaping of the 930 shield is not correct for mounting it on a non-930/SC rear trailing arm.