OK, in the years '82-'87 when V-belts were in use, there seems to be 3 different bracket styles and 3 different sized pulleys. One bracket setup does not have the square hole used for belt tightening, it seems to be on the '82-'83 cars. The other two styles both have the square hole, but the brackets are shaped different. Both styles seem to be used in the same years. Does anyone know what determined which brackets were used on each car? Was it simply the factory they were built at?

I've had several '86 model year cars, and both bracket styles were common. BUT, there were also 3 different sized pulleys used this year. Why? They are easily identified just by looking at them. Also, some have the clutch wires plug in under the upper bracket, while others have the plug moved out past the bracket.

Is there rhyme or reason to any of it, or did GM just use whatever was laying around?

86-87 use a serpentine belt/V-belt setup. The serpentine belt drives the water pump and alternator, and separate V-belts drive the AC/power steering, and the smog pump. That could make up one of your variations.

That was in '85 too. I think the different style brackets may just indicate which factory the car was built at, because both were used in '86. I need to figure out which of my cars were built where.

I just don't understand the different pulley sizes though. Of all of the ones I have (even the compressors from parts cars that are labeled), I can't figure out what would determine pulley size. It's not a TPI/carb thing, and not even gear ratio. Two identical optioned cars can have two different pulley sizes.

And these are original compressors too, nothing had been swapped.

mid-'85 cars started to use the serpentine style belt for
the alt and W/P certain '82 early-85 high performance
engines(LU5/L69/LB9)also used deep groove pulleys on
the alternator and A/C compressors in order to reduce
the chance of the belt being thrown at high rpm

One of my compressors that has the large, deep groove pulley is from an '83 T/A. I do not remember if it was LU5 or L69 as I had both. My old '86 TPI Iroc also had the large, deep groove pulley... but my two current '86 TPI Irocs originally had the mid size pulley.

I do have two compressors from '86 LG4 cars that both have the smaller pulley.

I wonder if my old '86 was a fluke with a leftover compressor installed. I do remember that with the AC on and at idle in gear, there was a resonance inside the car. The others did not do that.