The Founders were classical liberals, not modern day American liberals. The United States of America and its Constitution were founded on classical liberal principles, not modern day ones. If you don't know the difference you won't ever see the truth of that.
There is no difference in principle between the two. Those conservatives who think there is are confusing ends and means. Liberalism is now and always has been about equality, about serving the interests of the many instead of the few, about protecting the liberty of ordinary people against oppression by the rich and powerful. "Classical" liberals as you call them often focused on the government as the main tool by which the rich and powerful oppressed ordinary people, hence your confusion.
Actually, liberals still oppose oppression by the government. But there is now a greater willingness to use government itself to restrain oppression by private power. And yet even back then, this was not unheard of among liberals; I refer you to Jefferson's letter to Madison while he was serving as ambassador to France, in which he spoke movingly of the great inequality of wealth he saw, and certain taxation and free-land measures that he thought might prevent its occurrence in the United States.
You sir are badly misinformed. No difference?
Classical liberals wanted and want a central government that secures our rights and then leaves us strictly alone to govern ourselves and live our lives as we choose individually and/or collectively.
Modern day liberals want a strong central government that defines and assigns our rights and that orders society and provides for it.
The difference is self governance (classical liberalism aka modern day American conservatism) versus being governed (old style conservatism aka modern day American liberalism.)
Classical liberals believe in the sanctity of property rights and the unalienable right of a person to pursue life, liberty, and happiness whatever that means to him or her short of violating the rights of somebody else.
Modern day liberals believe in the collective, that it is right and good for the government to take what the rich earn or possess and give it to those who have less.
Classical liberals understand how corrupting it is to those in government and to those who are the beneficiaries of government largesse when the government is allowed to dispense any form of charity.
Modern day liberals do not trust their fellow man to do the right thing in matters of charity and look to the government as Big Brother, Source of all Benevolence, Benefactor to all ion need, etc. etc. etc.'
Classical liberals understand and promote a free market as the best hope of all to rise above the circumstances they were born into and want regulation only as necessary to prevent people from violating the rights of others or preventing honest competition.
Modern day liberals look to the government as the agent to change the circumstances people are born into, who resent the self made rich, successful, and economically powerful, and in effect look to government to restrain some of the success and reward the less successful.
I could go on and on and on, but obviously any who would think there is no difference beween cllassical liberalism and modern day American liberalism are either hopelessly uneducated/misinformed and/or extremely naive and/or intentionally dishonest. Take your pick.