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The latest problem on the new Orange Line cars? A thin piece of synthetic material about a foot long

In March, a new Orange Line train derailed just outside the MBTA’s Wellington Station. Though T officials at first pointed to track work, they now cite flaws in the train itself.
In March, a new Orange Line train derailed just outside the MBTA’s Wellington Station. Though T officials at first pointed to track work, they now cite flaws in the train itself.Matthew J Lee/Globe staff

When one of the few new trains to have graced the Orange Line derailed in March and disrupted subway service for weeks, transit officials at first suggested it was unlikely the problem was caused by the vehicles themselves.

And since the derailment occurred along a section of track that was undergoing repairs, it seemed likely at the time that the culprit would be aging rails or a faulty switch, not brand-new train cars. Still, as a precaution, the Massachusetts Bay Transportation Authority pulled all the new subway cars from service — four trainsets from the Orange Line and one from the Red Line — while investigating.

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The caution, it turned out, was warranted. Following a series of tests, the MBTA last week revealed that the undersides of the new trains are not turning properly as they accumulate more miles — an effect that officials now say played a key role in the March 16 derailment.

“When we first pulled these cars from service after this derailment, we were not expecting, really, to find what we found,” deputy general manager Jeff Gonneville said. “I’m glad that we did, and I’m glad we’re finding this now, and I’m glad we’re addressing this issue so these cars will be able to operate reliably in the future.”

The episode marks the latest setback in the troubled rollout of the new trains. The MBTA has a nearly $1 billion contract with a Chinese rail manufacturer to build 404 cars to replace the entire fleet of aging Red and Orange line trains. But repeated delays, including stoppages during the early days of the pandemic, have put the project well behind schedule. Only a few trains have so far carried passengers, and briefly at that, as technical problems have forced them out of service — sometimes for weeks on end.

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The latest issue centers on a part that few riders will ever see, called a side bearer pad. It’s a thin strip of synthetic, resin-like material, about a foot long and five inches wide, wedged between the heavy machinery of the vehicles’ trucks, which carry the wheels, and the bolsters, which connect the trucks to the cars’ bodies. Each train consists of six railcars, and each car has four of these pads.

They are designed to create a certain degree of friction — not so much that the truck struggles to move, but enough to create some resistance and prevent fast-moving cars from losing control.

The pads, however, appear to be wearing far faster than expected, creating more resistance to turning than they should. The friction is roughly double compared to when the cars were first introduced, making it more difficult to navigate track, Gonneville said.

“There’s a fine balance between what is an acceptable level of resistance to moving,” he said. “There’s a certain amount of force or energy . . . to put on the truck frame and the wheels, to have those wheels turn. If the resistance to that is higher than it should be, then you will climb up over the rails, which is what we had here.”

However, the manufacturer, CRRC, appears not to fully agree with the MBTA’s analysis.

Lydia Rivera, a spokeswoman for CRRC’s Massachusetts subsidiary, at first said the company “did not find any car-related factors that caused the derailment.” She later clarified that “we anticipate several contributing factors will be identified. If the bolster pad is identified [as] a factor it will be minimal.”

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But the MBTA has described the pad malfunction as a “key contributing factor.”

It may turn out there were multiple aggravating factors, said Piers Connor, a UK rail consultant. The friction caused by the prematurely wearing pads could combine with aging track and an especially tight curve to result in an incident as troubling as a derailment, Connor said.

“The tighter the curve radius, the more ‘twist’ applied to the pads . . . and the more resistance to the turning motion,” Connor said. While Connor stressed that he has no specific knowledge of the MBTA’s circumstances, he added: “Bad track doesn’t help.”

The bearer pads are standard on railcars, and built into every MBTA train in some form, Gonneville said. But the MBTA had not previously seen pads wearing out after so few miles.

The T has yet to figure out why they are failing, and such a determination will require close examination of their chemical makeup. But the agency is considering replacing the pads with a new type from a different manufacturer, though that could require new rounds of engineering and testing that could last months — keeping the new cars out of service for yet another long stretch. Gonneville, however, said he is optimistic they won’t be offline long, as he believes there are short-term solutions to mitigate the friction issue for the time being.

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CRRC is by some measures the largest rail manufacturer in the world, producing trains across much of Asia and South America. But its American outfit has struggled with the Red and Orange line cars, which are partially built in China but given final assembly at a plant in Springfield.

In October, MBTA officials announced that the final delivery of subway cars will be delayed until late 2024 — about a year later than the prior schedule, and a full decade after the MBTA chose CRRC to replace its trains — due to a cascading series of manufacturing and production issues at CRRC’s facility that were worsened by the pandemic, but also predated it.

The provenance of the bearer pads is deeper in the supply chain. The trucks for the subway cars are built for CRRC by Australia-based subcontractor Bradken Co. Bradken, in turn, gets the pads from another company, which Gonneville identified as Tenmat, of the United Kingdom.

Gonneville declined to discuss potential penalties or fines for any vendor, emphasizing that the various parties are, for now, focused on finding a solution rather than sorting out financial liabilities. The MBTA, however, has previously said it plans to fine CRRC for production delays.

Despite the seeming turbulence of the Red and Orange Line project, rail experts insist it is normal for transit agencies to run into trouble as they introduce new vehicles to service.

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“Trains don’t work out of the box because the client demands specific design details,” said Connor, the UK consultant. “What can go wrong, will go wrong. But, remember, a rail fleet is meant to last for 40 years, so the problems will be sorted out and eventually the trains will become reliable enough to serve the city effectively.”

Bradley Clarke, a transit historian and president of the Boston Street Railway Association, added that sometimes there is no way to know of a problem until new cars have been carrying passengers for a prolonged period. Though these cars are still new, it wasn’t clear the bearer pads would fail until they had accumulated tens of thousands of miles. That may prove true with other parts, too.

“You get a few seasons of air conditioning in service, and that will begin to tell you what tends to fail there,” he offered as an example.

Gonneville likened the trouble with the new cars to a period last decade, when the MBTA faced similar challenges with the delayed introduction of 75 commuter rail cars built by Hyundai Rotem. Those cars were plagued by a number of mechanical problems, including with doors, air conditioning, and brake systems. But since addressing them, Gonneville said, those cars have generally worked well, and he remains confident the new Red and Orange Line cars will, too.

”The more seriously we take these issues today, and the more we proactively address these issues today, the better these cars are going to be long-term,” he said.