My ‘65 Impala (283/4spd) has only one rear “upper control arm” If that’s what it’s called. There is one on the pass side but not the drivers side. The brackets are there. Could that be correct/appropriate? Does not seem to effect driving.🤔
Only cars that had a factory installed engine that was rated above 300 horsepower received the second control arm. They also got a 3/8th inch instead of a 5/16th inch fuel line, a thicker radiator and a stronger rear end as well.
What Big Dave says is true with the exception of the cars that were ordered with F40 HD suspension. I have a 66 that was a 283/3 on the tree originally. It's a Canadian car that was ordered with F40. The factory diff in it is a 3.07 ratio 12 bolt with 2 upper control arms.
F40 was an option in the RPO book that could be added to any car or truck. You got not only the missing upper control arm but stiffer springs and HD shocks, front and rear sway bar, with a larger than stock front sway bar, and heavy duty brake shoes from the factory. Posi was not part of the F70 option (that required a G70 RPO code to be added) but the two where often ordered together.
F-40 was referred to as the Heavy Duty suspension option. It included a 15/16" front sway bar, heavy duty shocks and upgraded springs. No rear sway bar and nothing different as far as brake shoes go. Metallic brakes were a separate option that could be ordered independently.
F-41 was referred to as the Sport Suspension option. That included the 15/16" front sway bar and a rear sway bar along with special shocks & springs. Ordering F-41 was the only way a car would be factory equipped with a rear sway bar.
In Canada at least, F40 didn't get you the 15/16" front bar. It only got you shocks, springs and that extra upper arm. My 66 was a 41,000 mile original car when I got it and it had the small bar. (a problem I corrected!)