mark kibort

that is not a centering diameter of 85mm, as nothing touches or is near this opening. its just a window for the bearing cap.

the ID is porsche, because the roots of this rotor are porsche. 157.1mm the S4 and I believe the earlier cars use this centering diameter on the ID.

the setscrew is not a big deal, unless you want to carve one out on the 928 hub face. better to just drill a hole in the rotor that matchs the stock 928 set screw and use it. its not needed other than for convienience.

mk

xschop

Until I get a later 928 hub in hand and a true tech drawing of the early & later 928 rotors, I am a little suspect. The tech drawings for the early and late 944 rotors have a 155mm hub interface. Centering such a large 330mm rotor would be critical for high speed balance.

mark kibort

the good news is that the 330mm rotors have the same ID spec. Im not sure about the 79 and 84 cars, but that should be easy to check. if its only the alignment, just drilling a simple hole in the rotor hat that matches the hub set screw is an EASY fix or assurance of good balance of the rotor when spinning.

might have a sample of the adaper plate this weekend or early next week. then, a test with the actual '82 car set up and see how much caliper griding we will need to do. I suspect that will be the easy part.

mk

xschop

When I get a later 928 hub in hand I will report that info in my billet hub thread. I'm glad you guys can get some bigger/better brakes on the Early cars inexpensively.

mark kibort

Here is the part i plan to use (test), made of wood. maybe if it proves itself, it will turn into 6061 like Pinocchio

edited. Part was wrong . cut out area was on the thin side, should have been on the thick side.

brianrheffron

Mark, to get your adapter plates spot on you could try this.
Make up two pieces in steel, one that bolts to the upright
and one that bolts to the brake calliper.
Bolt the adapter pieces to upright and to calliper then
move calliper into desired position on disc.
Get assistant to put brakes on then tack weld the pieces together.
You now have a "buck" with the bolt holes in the ideal relevant positions.
Use the dimensions of this buck to machine the actual adapter from steel.
Done this in the past and it works very well. It allows you to get the
pads/ calliper right on the edge of the disc maximising the swept area.

76FJ55

With manual machining capabilities like this who needs a CNC?

Actually woods great. Eeasy to manipulate, to find the ideal position, and then use as a template to make a functioning part.

I'm excited to see a larger rotor all mocked up to verify proof of concept.

pcar928fan

Can't wait to see this all finished up for my EURO85 car! Then I will want Dwayne to do a full write upon it with pics of course!

mark kibort

what material should I use for the finished product? steel, alloy? let me kwow, or what I should NOT use too.

The bolt centers are 24mm apart, and the holes themselves are 12mm diameter, so that only leaves a half an inch of thickness between them. something to be concerned about?

Mk

xschop

I've built many different brackets with 1/2" and less between bolt walls using 6061. The only unknown from the drawing/mock-up I have is the arch, but it goes thru the thickest part and the rest is plenty beefy. I designed an arched set of adapters for the RX7 brakes on the rears of these cars and it is mega strong thru the arch area. It wouldn't be a concern here either. I usually start with lexan or delrin for mock-ups, whatever is lying around....

IcemanG17

The good news is whatever part you need Sean can make real easy..... I would imagine if you got it scanned into the CAD program that he uses you could even email it to him!!!!

xschop

1" x 2.5" 6061-T6 is common stock and not that expensive. I would CNC the arc in the brackets to get maximun strength. Don't forget that the bracket/mounting holes are subjected to axial forces and not being pulled radially (outwards).... This diagram keeps 1/2" billet around the mounting holes at all points at 1/2" thick too....

xschop

If you need to you can clearance the spindle ears at the bracket edge with a 1" end mill just in that area.
Also as a side note, I would put my money on 1/2" billet over the 7.25mm of cast iron 928 spindle ear in a stress test.

mark kibort

I got to scots house and started to play around with the rotors and wood mock up of the adapter. I cut out the wrong side (should have been the thick side) but then that was fine as i was trying to find out what the clearance issues were going to be.

looks like a pretty straight forward fit.

Notice the clearance to the lower ball joint. sure looks like there is room for S4 rotors,but looks can be decieving.

Looks like its a breeze to file down the edges of the caliper. it will be only a couple of mm's or so and the piece of that bridge is solid cast iron.

pcar928fan

Can't wait to see this happen!