The nice thing about legislation is that it leaves a record - usually a long one. With regard to crack/cocaine, there was a 100:1 sentencing disparity - 5 grams of crack => the same sentence as 500 grams of cocaine. The best place to look is the record itself.

Of course, the problem is that there's rarely only one motivation for something. Congress, when passing sentencing guidelines for crack versus cocaine, did not overtly mention race. They did mention it repeatedly when they came to seek repeal of the old guidelines.

Joe Biden, one of the drafters of the legislation, said:

In 1986, crack was the newest drug on the street, and Congress was told that this smokeable form of cocaine was instantly addictive and that its effect on a child if smoked during pregnancy was far worse than that of other drugs and that it would ravage our inner cities. I remember one headline that summed it up well, and it read "'New York City Being Swamped by 'crack'; Authorities Say They Are Almost Powerless to Halt Cocaine.'' And they called it "the summer of crack'' in that headline.

He then went on to explain how the foundational beliefs were mistaken. With regard to race, he said:

The past 21 years has also revealed that the dramatically harsher crack penalties have disproportionately impacted on inner-city communities, the African-African community: 82 percent of those convicted of crack offenses in 2006 were African-Americans.

So you can see his (post-hoc) position is that race was not a factor.

Likewise Jeff Sessions, a federal prosecutor at the time, testifying about repeal of the discrepancy:

Now, I do remember, just like you said, Mr. Chairman, I was a prosecutor in the mid-1980s. Crack started arising, and people predicted it would spread. And it shocked me how fast it spread to rural Alabama--not just an urban area like Mobile, where I was, but throughout the rural areas. [. . .] But I think we are at a point now where this 100-to-1 disparity that does fall heavier on the African-American community simply because that is where crack is most often used has got to be fixed. I want to join you in this, and let's do it this year. Let's get it done.

Likewise Russ Feingold:

The disparity in sentencing between crack and powder cocaine offenses is a serious blemish on our system of justice. Over the past 20 years, it has become clear that neither public health nor law enforcement considerations justify the disparity. To the contrary, its effects are pernicious. It diverts resources to low-level offenders and exacerbates overcrowding in Federal prisons, and it has a dramatically disproportionate effect on African-Americans, which undermines confidence in the Federal justice system in many communities.

Source: Senate subcommittee hearing, 12 Feb. 2008, available here

It is hardly surprising that with the benefit of hindsight, these people who were responsible for passing the law will disclaim race as a motivation while passing it but claim race as a factor for repealing it.

The US Sentencing Commission had this to say about the 1986 act:

Congress's conclusions about the dangerousness of crack cocaine relative to powder cocaine flowed from specific assumptions. First, crack cocaine was viewed as extraordinarily addictive. This addictive nature was stressed not only in comparison to powder cocaine (i.e., crack cocaine is "the more addictive . . . substance" 132 Cong. Rec. S8092 (June 6, 1986) (statement of Sen. D'Amato regarding S. 2580). See also 132 Cong. Rec. S14,293 (Sept. 30, 1986) (statement of Sen. Bumpers).) but also in absolute terms. Second, the correlation between crack cocaine use and the commission of other serious crimes was considered greater than that with other drugs. Floor statements focused on psychopharmacologically driven, economically compulsive, as well as systemic crime (although members did not typically use these terms). Third, the physiological effects of crack cocaine were considered especially perilous, leading to psychosis and death. 132 Cong. Rec. 26,447 (Sept. 26, 1986) (statement of Sen. Chiles). Fourth, members of Congress felt that young people were particularly prone to using crack cocaine. This was mentioned in debate as one of crack cocaine's most troubling features. Finally, there was a great concern that crack's "purity and potency," the cost per dose, the ease with which it is manufactured, transported, disposed of, and administered, were all leading to widespread use of crack.

Source

Any sort of effort to intuit the effect of race on passage of the laws would be based on foreknowledge - that Congress knew the disparate impact. If you read "gangs" or "inner cities" as "disproportionately african-american neighborhoods." At least from a legal perspective, disparate impact claims are almost ineffective as a tool to prove pernicious intent, and what the hearings show is that's what you have - disparate impact, not racially-charged intent. You could argue that Congress should have known the disparate impact and therefore racial animus was at least a secondary cause. And for that matter, taking over 20 years to repeal it is indicative that the problem was not on the front burner.