[AROWHED]

Regulars here have likely seen the Plan B post about trying to find a floating disc brake rotor to fit the 65-66 drum hub and work with 67-70 factory disc brake parts. While I haven't entirely given up on that, I also have not yet come across what I'd call the ideal rotor to use, as many specific rotor dimensions must be met and all the hundreds I've checked so far seem to fall short in one dim or more.

But did come across an integral hub rotor that is particular to fullsize Pontiacs and other GMs for one year only: 1977. On Rockauto it is listed as Bendix # PRT1156, or Raybestos 5028R. It has all the correct dimensions to retrofit a 67-70 front disc setup onto the 65-66 drum spindles, even the same A2 and A6 wheel bearings. (But that also means it does NOT work as direct replacement rotor for 67-70 factory front disc, since they use different wheel bearing sizes.)

HOWEVER there is always a catch: The inner wheel bearing is recessed 3/8" of inch further into the rotor than what is needed to position it correctly on the B body drum spindle. This means a 3/8" thick spacer must be used between the inner bearing and the spindle, and therefore that spacer must act as the contact surface for the wheel seal as well.

To create a spacer, ordered a bronze sleeve bearing from Grainger, item# 49YU61:

https://www.grainger.com/product/BUN...searchBar=true

Its 1.250" inner diameter matches the spindle. It's 2.000" outer diameter matches the 1977 rotor wheel seal (Timken #8871). So it was just a matter of cutting a 3/8" thick piece off and with a lathe, true it up and add a recess bevel on the inner diameter to clear the radius on the spindle so the spacer sits flat against the wheel seal surface shoulder. Also polished the outer circumference smoother.

Photos show the required positions of the A2 and A6 bearings with the added bronze spacer on a 66 drum spindle, the 1977 rotor with its Timken 8871 seal riding on the spacer, and then all of it assembled: 66 spindle, 77 rotor and 69 Pontiac B body disc brake caliper bracket and D52 caliper. Caliper and brake pad positioning is perfect.

For what its worth: It crossed my mind that moving the inner wheel bearing 3/8" further out on the spindle is not ideal. The drum spindle is 1.250" thick at the inner bearing, while a 67-70 factory disc brake spindle is 1.377" (and uses A3 and A5 bearings). I cannot speculate that in doing so it may increase the chance of failure of anything. Like any modification beyond factory that is done to your car, you do so at your own risk.

[PONTIAC LARRY]

interesting, i was looking at 71+ 2WD C10 11" rotors (5x5) specs a while back comparing bearing type to the 70 Bonneville factory discs I put on our 66 Chief and during that I found the caliper interchange with 4WD 71+ K5 K10 application and the 69-70 single piston Pontiac B units
Looking at those bearing sets for 70 Bonne disc inner as A5 and outer as A2 (not A3) and the 71+ C10 is A5 inner but A3 outer and the 71+C10 rotor fits 71-76 B body Pontiac

[AROWHED]

Yeah the 71-76 guys still have a new rotor source, for now. 67-70 do not, as far as I'm aware.
I'm just trying to find a low buck approach to putting discs on 65-66 using factory parts and keeping the drum spindles in place. I am not familiar with 64 and older spindles...so don't know if it's possible this method can work for those years or not. Anybody know interchange on spindles for 1960-70?

[Scarebird]

Originally Posted by AROWHED

Anybody know interchange on spindles for 1960-70?

1959-64 deep offset upper boss, 7/16" lower holes

1965-66 shallow offset

1967-68 1/2" lower holes

1969-70 different offset, spacing and bearings

[Zooguy]

Very interesting and helpful