Like clockwork, the cars start showing up at 7:30 a.m. sharp.

Before that, the streets of Ann Arbor are quiet but for a single garbage truck. The sky is dark, lit only by a crescent moon. At Michigan Stadium, the lights are still on.

A few more garbage trucks circle the concourse inside the stadium and the parking lots outside, picking up the trash from dumpsters. Later, volunteers from Eastern Michigan will come to finish the job on the parking lot. And then there is the stadium bowl.

At 10 p.m. the night before, hours after the Michigan football team polished off a 41-8 win against Illinois, the bleachers were a mess. After every home game, it stays that way until early the next morning, when families from nearby Father Gabriel Richard High School come to clean it up.

Fewer than 600 students go to Gabriel Richard, but before sunrise, many of them are already in the top rows of the bowl. Often more than 300 people come out to help every Sunday — today, that number is 323. One hundred ninety-seven of them will stay for Mass.

But the Catholic school’s religious foundation goes beyond Father Richard Lobert’s hour-long service. In the mind of Cindy Pressprich, one of the coordinators of Gabriel Richard’s effort, the school pairs the clean-up effort as a community event with the usual Sunday Mass. The students can even use the hours as credit toward their service requirement.

“It really has to put our belief in action about respecting each other, being charitable, believing the best about people,” Pressprich said.

Pressprich arrives with sign-up sheets and paperwork for all of the volunteers. The school has asked families to help out after five of Michigan’s eight home games this season. The Michigan Athletic Department pays Gabriel Richard — Pressprich doesn’t know how much, perhaps, she says, because it has been a near-constant agreement since the mid-1970s — through the school’s general fund, which helps defray tuition costs.

There’s little talk of administrative matters when everyone shows up in the dark, though. When Pressprich brings the forms, some families are already in the stands, using brooms or blowers to confine the trash to the lower part of the bowl. Then, other kids help out with picking up garbage, recycling pizza boxes and throwing away half-eaten pretzels.

Meanwhile, Pressprich directs people at the entrance and co-coordinator Jerry Bonar drives a golf cart around the concourse to supervise. Both parents are central figures in Gabriel Richard’s effort, each with seven kids. Both have been helping for years, with some kids now graduated from college and some just entering high school.

Pressprich’s leadership at the front gates helps the operation run smoothly. Bonar’s enthusiasm — in the early hours of the morning after the Chicago Cubs clinched a trip to the World Series, he cried out to one volunteer, “Hey, hey, how ’bout them Cubbies?!” — keeps everything upbeat.

It’s a tough job, but within two hours, the trash is all in bags at the bottom of the stands as the dumpsters come by to pick them up. The 197 volunteers all shuffle off to Sunday Mass at the Junge Center between the Big House and Crisler Center. Sometimes, Mass is in the north end zone if it’s not too cold. Those days are probably over for this year, but the temperature won’t keep Gabriel Richard away.

“Attitude is everything,” Bonar said. He recalls a famous quote: “Pain is inevitable. Misery is optional. Choose joy.”

For Bonar, though, it can also be tough to manage hundreds of volunteers.

“It’s the balance of motivation without any type of tangible reward,” Bonar said. “People go to work, recognition and money. I don’t have any money to work with. I just have recognition. I have thank-yous. I have a smiling face. I have enthusiasm. I have all those intangibles.”

Naturally, in cleaning a bowl that seats 100,000-plus, the Gabriel Richard volunteers must account for variables. When the Athletic Department renovated Michigan Stadium in 2010, it added space to the concourse, which now requires 30 or 40 people to clean up instead of six or eight.

Stadium promotions sometimes add wrinkles, too. If Michigan hands out pompoms for big football games, Gabriel Richard shows up the next day to find thousands of them on the ground. Another time, the fans held up individual posters that together honored Lloyd Carr. Gabriel Richard had to peel them off the bleachers and clean them up. “That might have been the all-time rough one,” Bonar said.

The biggest hope Bonar has every week, though, is for the weather.

“I don’t care what you have — (we want it to be) dry,” he said. “I don’t care if it’s minus-3. If it’s dry, we’re OK. Wet is the worst.”

Gabriel Richard has cleaned the bowl with 70 people and with 400, in hot weather and in cold. The seasons change over the course of the football season, sometimes until debris has frozen over on the bleachers and the volunteers have to chip it off.

But Bonar doesn’t have a problem with variability. That’s part of the appeal of the job — it comes after every home game, no matter the weather, no matter the year, between all kinds of people. According to Bonar, some parents who help out are chief executives or presidents of companies, but they still spend their Sunday mornings at the Big House. The families team up, three to a section, and it’s clear most everyone knows everyone else.

“We’ve got all walks, from the whole gamut,” Bogar said. “These folks could easily write a couple-thousand dollar check and stay home, but they don’t, which I think is really good.”

Added Pressprich: “This is a pretty lowly task. Everybody wants to be better than garbage — I mean, ‘Why am I here on a Sunday morning?’ ”

In two weeks, Michigan returns home to play Maryland. At some point between the end of that game and nightfall the next day, the Big House will be spotless again. It doesn’t happen on its own.