So, I purchased my first RX-7 about a month ago and I recently tried changing the front pads and rotors on it. My overall goal is to return as much of this car to factory spec as I can within reason given parts availability. It is a 1985 GSL with rear discs and LSD. All the brakes are shot, so I wanted to start with the fronts and I ordered the "Front Brake Rotor Set - 1984-1985 Mazda RX7 GSL - Dynamic Friction Part Number: 8599-06346473" from Parts Geek as well as some pads and brake hardware.I removed, inspected, and repacked the bearings with fresh grease after removing the old rotors and was surprised to find that the outer wheel bearings, races, and caps currently on the car don't fit with the new rotors. So I busted out the micrometer and got to measuring (see pics below).

The old rotors have a diameter for the outer bearings measuring 40mm, whereas the new rotors measure 47mm. The outer bearings and races I have measure right around 40mm for their outside diameter, so there's no way they'll work with the new rotors. I also measured the bolt pattern on the new rotors which came to 4x110, so I know they aren't for a GSL-SE or any newer RX-7.

I don't know what to do next. I obviously need new outer bearings and races that FIT with the new rotors, but I have zero clue of how to ensure they'll fit the new rotors before they show up. I don't know if the rotors are the issue and I just need to get a different set OR if the previous owners put a weird size rotor and bearing on and I'm putting on the correct sized rotor again. Its also weird to me that ONLY the outer bearings don't fit. The inner bearings and races fit just fine. I'd rather not buy parts at random until I get a set that matches, so I'm looking to the community here to help.

In my confusion I did some googling and found a few promising sources:
- Essex Rotary has a Bearing Set SKU: ERS-FB-FWBS at the following link: https://essexrotarystore.com/product...or-rx-7-sa-fb/. That said, there are no pictures or measurements provided.
- Mazda sells 1391-33-075-MV Wheel Bearing at https://www.mazdapartsnow.com/genuin...tra2=&filter=(). That part is described as a "Taper Bearing Rx7; Outer Front". I think this is the most promising but it still doesn't contain any measurements to ensure it'll fit the new rotors.

Anyway, what do you all think? Are my new rotors the problem? Are the old bearings the problem? Am I the problem? Any help is appreciated!


side by side comparison

Dynamic Friction Rotor

Unknown Brand/Age rotor

 

I feel silly updating so soon after posting, but I found an answer to one of my questions...

I had asked earlier if I had the wrong sized rotor or bearing. I know now I have the wrong sized rotor. On RockAuto, "https://www.rockauto.com/en/catalog/mazda,1979,rx-7,1.1l+r2,1192227,brake+&+wheel+hub,wheel+bearing, 1672". The bearing is described as "Engineered and tested to OE specifications which guarantee precise fitments".

The item specs are as follows:
Bearing Shape Cylindrical
Inside Diameter 0.688in
Outside Diameter 1.570in
Type Taper Bearing
Width 0.420in
Width 0.575in

If you convert 1.570 inches to mm it comes out to 40mm, so I'm pretty sure my rotors are the issue...

 

The 1979 to 1983 are small bearing and the 1984 to 1985 are big bearing.

The outer bearings on the 1979-1983 is smaller (40mm) and the 1984-1985 is 47mm.

Looks like someone might have been sneaky and converted your car to small bearing or installed the wrong rotors somehow.

 

Thanks! I was just digging through RockAuto and found the differences between 79-83 and 84-85 right before you replied. Came to that same conclusion. Either way, thank you for confirming my suspicions.

 

For anyone running into the same issue as I have, if you're replacing front rotors, be sure the bearings you purchase or re-use match the Cup Outside Diameter of the rotor you are buying. RockAuto helps a ton because you can see all the measurement info in the item descriptions.

To correct my little issue, I'll be purchasing the following from RockAuto:
- BCA NBA32 Bearing & Race Set Front Inner; Taper Bearing Set
- BCA NB32204 Bearing & Race Set Front Outer; Taper Bearing Set

The Outer Set matches the 47mm Cup Outside Diameter of the rotor Dynamic Friction rotor previously mentioned in the original post and SHOULD fit just fine.

 

I'm now running into a different problem...

The bearings/races that I ordered all fit in the rotors perfectly. No issues there. HOWEVER, when I seat the rotor on the spindle and then try to tighten the nut to set pre-load, the rotor is really loose no matter how tight I go and I think I know why. From what I can tell after playing with it for the better part of two hours today, it looks like the inside diameter of outer bearing is contacting the spindle where it tapers larger and that is preventing the bearing from being fully seated in the race. The outer bearing is about 2-3mm from fully seating in the race which means the rotor can wobble quite a bit. I've triple checked that everything is pressed in fully and that the wheel seals are on correctly too. I'm lost as to why my shiny new parts don't fit, but I have a theory...

Since we established that the previous owners "converted" my car to smaller bearings, is it possible that the spindles are different too? Is there a slight difference in the taper and diameter of the spindles between model years such that my 47mm outer bearings just barely won't slide all the way in?

I was really excited to have this done today and ended up making no progress. I'm desperate for help, guys. If it isn't the spindles being different then don't understand what the issue is...