Former car capital of America (6)
I believe the answer is:
austin
This clue might be a double definition.
'former car' is the first definition.
'austin' can be an answer for 'car' (I have seen 'old car' mean 'austin' so perhaps 'car' could also mean 'austin'). I am not certain of the 'former' bit.
'capital of america' is the second definition.
'austin' can be an answer for 'capital' (state capital of Texas). I am not certain of the 'of america' bit.
Can you help me to learn more?
(Other definitions for austin that I've seen before include "Texan city" , "The capital of Texas (6)" , "State capital of Texas" , "Capital city of Texas" , "Engineer" .)