(Adds background, Garrett Camp memo)
SAN FRANCISCO, Aug 10 (Reuters) - Ride services company Uber Technologies Inc's head of operations, Ryan Graves, a long-time ally of former chief executive Travis Kalanick, is stepping down from his full-time job at the company, according to a copy of a letter from Graves seen by Reuters.
Graves will continue to serve on Uber's board, it said.
The company is looking for a new chief executive after Kalanick was pressured to step down, following a series of business embarrassments for Uber.
There has been some speculation that Kalanick could return to the top job, but events this week cast doubt on that possibility.
Graves said that he preferred to make his own move before the new leader was chosen.
"It's really important to me that this transition doesn't take away from the importance of the onboarding process of our new CEO, whoever that might be," he wrote.
Earlier this week another longtime Kalanick ally, co-founder Garrett Camp, sent a memo to employees saying that "Travis is not returning as CEO," according to a copy obtained by tech website Recode.
Kalanick, Camp and Graves together hold a significant voting stake in Uber.
Kalanick's pugnacious style largely defined Uber's approach and helped it become a transportation colossus valued at $68 billion, the largest private firm backed by venture capitalists in the world.
But that brashness has also been blamed for a string of scandals this year, from the unearthing of a culture of sexism and bullying at Uber to a U.S. Department of Justice federal investigation and a high-stakes lawsuit filed by Alphabet Inc's autonomous car division, Waymo, that threatens Uber's self-driving car ambitions.
Graves was one of the first employees at Uber. His memo was reported earlier by CNBC. (Reporting by Peter Henderson in San Francisco, additional reporting by Laharee Chatterjee in Bangalore and Heather Somerville in Palo Alto; Editing by Phil Berlowitz)