Uber acknowledged Monday that it had modified some of its electric bikes recently after the company encountered a braking problem similar to the one that prompted rival Lyft to recall its own electric bikes in several cities over the weekend.

Uber, which operates a popular electric-bike-share service known as JUMP, said the brakes on its JUMP bikes were modified more than a year ago to smooth out the brake response and make the process more gradual. Lyft moved this weekend to recall its electric bikes after some riders reported that the front wheels could seize up, causing them to slip or fall.

Lyft said that up to 15 percent of its overall bike-share fleet would be recalled and that manual bikes would be used to fill out the fleets. Through its Motivate subsidiary, Lyft operates New York’s Citi Bike, Washington’s Capital Bikeshare and San Francisco’s Ford GoBike.

Uber and Lyft bikes both rely on a braking system from Japanese manufacturer Shimano. But spokesman for Shimano said Tuesday its braking system, the Shimano BR-C6000-F front brake, was not at fault, raising the question of whether the part itself was the problem or whether it was not deployed to manufacturer specification.

“Shimano provides specification requirements for bicycle manufacturers to refer to when designing bicycles,” the spokesman said. "When designed and assembled to these specifications the brakes perform to global standards. With regards to this specific case, based on the information we have, this is not a Shimano brake issue.”

Uber and Lyft are making forays into the bike and scooter markets as part of their long-term business strategies, as Lyft went public late last month and Uber is set to list its shares on the stock market in May. The companies are trying to diversify their mobility options beyond the traditional ride-hailing model.

An Uber spokesman said Monday that the company had modified bikes with the braking problem as it moves to introduce a new bike model across the country. While 100 percent of the San Francisco fleet consists of the new bikes, Uber said, JUMP operates in several other cities, such as Washington, New York and Austin, where it still uses the old model for at least some of its fleet.

Uber said it expects that 100 percent of the JUMP fleet will be upgraded to the new model in the coming months.

“Late last year we introduced an updated model bike with a new brake system,” Uber spokesman Matthew Wing said in a statement. “Our older bikes have Shimano brakes but with a hardware modification to improve braking."

Uber declined to say when it first learned of the issue, when the bikes were retrofitted or why it didn’t publicize the safety change earlier so that Lyft could have taken similar action.

Lyft said its decision came in response to incidents in which tapping the brakes led to stronger-than-anticipated force, causing falls.

“After a small number of reports and out of an abundance of caution, we are proactively pausing our electric bikes from service,” a Lyft spokeswoman said in a statement. “Safety always comes first.”

Users of the electric bikes had complained on social media of instances when the brakes seized up while in operation, leading to injuries and even some cases in which riders flipped over the bikes’ handlebars after sudden unexpected stops.