Tech Article: Vented-rotor Conversion
by Stephen Moffett
1977 280Z, original strut assemblies w/ KYB struts (new), completely rebuilt front-end, 15x7 Fast Wheels w/ 225-50-15 Falken tires (my rims have 3.75" backspacing), 1988 Toyota 4x4 (4-Runner) brake calipers, 1984 Nissan 300zx rotors, steel braided brake lines
This is the car that I did the conversion on, it works and I've been driving around like this for approx. 5 months w/ no problems. Everything that I write was measured according to my car. Things could differ for yours.
YOU MUST DO THIS FIRST (if you haven't already). Go out and get front brake calipers for an 1988 Toyota 4-Runner.
Go through the process of fitting these onto your car FIRST. They will fit on without any modifications (except cutting the heat shield, and actually you might as well take this heat/dust shield OFF, because you probably won't be able to use it with these rotors!)
AFTER you have gotten these calipers to fit, that is - they clear EVERYTHING (i.e. struts, wheels, tires...etc.) Now you can go buy your nice new '84 Nissan 300zx front rotors.
These rotors look just like the Z's except that the "hat" section where the hub bolts to, is shorter, therefore you will need a spacer to go in between the hub and the rotor.
The hub I used was the original one on my 1977 280z.
The way that I measured to see what size spacer I needed was to just measure the difference between the "hats" of the two rotors (1977 compared to the 1984). This difference when I measured it was .5 of an inch. This lead me to believe that this was an exact difference (I mean that Nissan made these exactly .5" different). It may for some strange reason be different on your car (as far as position relative to the caliper mounting bolts or something) - take measurements and find out exactly what size spacer you need.
You can make this spacer however you want to and out of whatever material you want. I chose to design the spacer on Auto CAD, just a 2-D drawing that I made into a .dxf file-type so that it could be cut using a CNC water-jet router.
I had a friend cut this for me out of .5" mild steel (I don't have any money, so you can certainly make this out of whatever material you think will withstand the shock, heat, etc.). This mild steel is a little heavy for me, but it was more than strong enough for the application).
***I still have the Auto CAD file of the spacer (like I said it's not that big of a deal), but anyway, if anyone wants the file I will send it to them. Or if anyone wants me to make the spacer for them I will do this.
After you have obtained this spacer you are practically done!! :) Just reassemble putting the spacer in between the rotor and the hub.
OH YEAH, I ALMOST FORGOT!! You will need to buy new bolts to secure the rotor-spacer-hub assembly together. You can take the original bolts to the store and just get the next size LONGER. I couldn't find the size of the bolt that I used (I had it written down) I believe they were 40mm long, they fit perfectly, they use all the threads in the hub and don't stick out at all. These were obtained at Pep Boys, they are a metric grade 10.9. Get some new lock washers too.
Completely assemble the rotor-spacer-hub assembly back on the car (like I said earlier I couldn't keep the hear/dust shield on...you may find differently).
Now try to install the calipers without the pads.......anything....any sparks....did the car thank you?...mine didn't either.
You may find that you need to shim the calipers a bit. By this I mean that the rotor needs to fit right in the middle of the groove/track of the calipers (i.e. if the pads were installed the rotor needs to fit right between them). For some reason it may not fit perfectly. If you need to shim, just get very thin washers (good strong ones though) and put them between the caliper and the caliper mounting piece that is welded to the strut assembly. Make sure to put the same amount of shim at both of the caliper bolts so that the calipers stay straight.
Reconnect everything else, bleed brakes, and you're off.
I hope everyone is satisfied with the results, I have been.
Stephen Moffettis a Mechanical Engineering student at the University of Texas. He has a 1977 280z (turbo) intercooled with programmable EFI.