Assets for the nation's 5,893 credit unions grew 7.3% to $1.4 trillion in July from year earlier. Along with loan growth, savings grew 7.4% to $1.2 trillion and capital grew 6% to $146.8 billion.

Credit union loan growth was boosted by a nearly 15% increase in vehicle loans, which continued to outperform the market, and account for a larger share of credit unions' overall loan portfolio. New car loans grew 17.3% to $129.5 billion, while used car loans grew 13.3% to $201.3 billion.

U.S. unit sales of cars and trucks rose to a seasonally adjusted rate of 16.8 million per year in July. It was up from 16.7 million in June but 5.6% below the 17.8 million sales pace set in July 2016.

July's sales numbers were above the 16.5 million rate considered by economists to be the inherent demand for the U.S. auto sector.

"Auto sales will remain above this level for the next two years as Americans make up for the lack of purchases during the 2008-2012 time period, and consumers replace vehicles damaged during the recent hurricanes," CUNA Mutual Group economist Steven Rick said.

Credit unions' real estate portfolio grew at a more modest 8.7% over the 12 months. First-lien mortgages grew 9.3% to $375.5 billion in July, while second-lien mortgages grew 6.1% to $83 billion.

Rick noted that first-lien real estate originations in the first half of 2017 were 6.6% higher than in 2016's first half and home equity originations grew 26%. Credit unions held $458.5 billion of total real estate loans in June, accounting for 4.6% of the entire mortgage market, up from 4.4% a year earlier.

"The stage is set for another strong year of credit union first mortgage growth as rising purchase activity offsets slower refinance business," he said. "We expect the Federal Reserve to raise short-term interest rates in December 2017, which will lift the 30-year mortgage interest rate to the 4.25% to 4.5% range by the first half of 2018 and reduce the refinance business at financial institutions."

In other areas, credit cards grew 7% to $54.1 billion, and member business loans grew 10.5% to $73.7 billion.

Credit unions have added 2.9 million members in the past year, including 454,000 members in July. Rick expects credit union memberships to grow 4.0% in 2017 and 3.5% in 2018.