NBC Bay Area’s Investigative Unit has learned that Muni maintenance crews have been stripping parts out of brand new $3 million train cars for several months and using those parts to keep other trains in the new fleet running.

Two cars stored at a Muni yard in San Francisco have had their wheel trucks removed, rendering them inoperative. One of them, No. 2033, has many other key parts removed, including stairs, instrument panels and other computer equipment. The parts are shifted to other trains in Mun’s 68-car LRV-4 fleet. Currently, about 40 train cars are running and under warranty from train maker Siemens in Sacramento.

Muni officials said they were aware of a video obtained by NBC Area’s Investigative Unit showing car No. 2033. But they said a second idled car, No. 2012, was sideline because it had flat wheels.

“It is not at all like 2033,” said spokeswoman Erica Kato.

Muni workers say two other cars, Nos. 2001 and 2003, were sent back to Siemens facility in Sacramento, where they too are being used for parts. Kato did not respond to questions about those cars.

But, she said, crews “swap out parts all the time’’ on the new trains, as a matter of convenience. It allows them to quickly obtain parts without the delay and cost of getting them shipped from overseas.

The head of Siemens’ U.S. rolling stock division could not be reached for comment.

The head of Muni operators’ union, Roger Marenco, says the fact that new trains are already being raided for replacement parts makes it clear to him Muni’s new fleet is not holding up well.

“I’m not entirely sure what the point is of building a $3 million train, just to be picked on for parts to be scavenged on like a pick-and-pull junkyard,” he said. “It just doesn’t make sense.’’

“This equipment is brand new, they shouldn’t be going through spare parts that fast,” added Dennis Lytton, a transportation expert who has previously advised public transit agencies across the country on safety.

“It makes things progressively less safe to have to do that all the time,” Lytton said in an interview after reviewing the video. “So it makes you wonder, you know, if the vehicle Siemens has built is, you know, rugged enough to take this kind of operating environment.”

On Wednesday, Muni was forced to cut back to running mostly single car trains after a pin in one of the coupler systems broke.

Two days earlier, Siemens informed Muni that the coupler pins it has been sending Muni -- to replace problem pins identified in the spring -- are themselves defective and cannot be expected to last longer than three to four months without breaking.

San Francisco Supervisor Aaron Peskin, when asked whether Muni should be using parts from idled trains, responded flatly: “Not if they’re brand new.”

Peskin expressed skepticism about approving hundreds of millions of dollars more on 150 of the same problem cars.

“We’re going to get to the bottom of this -- and if it turns out their product is unfixable we’re not going to procure more of them, it’s just that simple.”