[runn141]

were the 12 inch brake rotors on all gm fullsize cars have a different lug pattern than the 11 inch? and does anyone know if the 2 will interchange on the same spindle?

[runn141]

i also found a set of drop spindles for 92-96 caprice/impala. can anyone tell me what the difference is between them and 91 on back? the part# for the balljoints are the same.

[joe_padavano]

Originally Posted by runn141

were the 12 inch brake rotors on all gm fullsize cars have a different lug pattern than the 11 inch? and does anyone know if the 2 will interchange on the same spindle?

The 12" (actually 11.75") rotors use a 5 x 5" bolt circle. The 11" (actually 10.75") rotors use a 5 x 4.75" bolt circle. They can't be swapped on the knuckles since the caliper bracket is an integral part of the knuckle and must be further away from the rotor centerline on the larger rotor.

[curtis73]

As a general rule, 12 inch rotors are typically 5x5. The reason is, if a full size car was HD and got the 5x5, it also got the 12 inch rotors. The same exact rotor in 5x4.75 can be found on WS6 F-bodies. Its expensive, but its the same exact rotor just drilled differently. Most non-HD fullsize and all intermediate/ponys got the 11" and they all had the 5x4.75. The only exception was the WS6 which got the 12", so they just redrilled the big rotor for the F-body bolt pattern.

The difference in the spindles is similar, but I don't recall it being a specific year change. There is a 11/16" ball joint and a 5/8" ball joint. The larger was used on many of the HD cars including 9C1 cop cars. Again, the spindles are the same, its just that the tapered hole for the bottom ball joint was drilled larger for the larger stud. Many of us Impala SS guys felt gyped by getting the smaller ball joints, so we swap in the HD ball joint (direct fit) and drill the hole bigger with a tapered reamer... or get the other spindles.

I can't tell you with a whole lot of certainty about other differences, unless it was cast with a different steering stop, or made for different calipers, but I do know that my 1973 Impala Station wagon uses the exact same rotors, calipers, pads, and bearings/seals as my 96 Impala SS. Not much changed from 71 to 97. I would say its pretty safe to assume that they're all interchangeable, and any differences would be academic and easily solved with a drill press.

You can go even further back with BOP b-bodies. I've swapped things back and forth between my 66 Bonneville and my 96 Impala. It had drums in the front so the spindles were totally different, but the control arms are interchangeable.