Or as the brothers explain on their website, working even one hour a week is too much. From "An Actual Semi-serious Note from Click and Clack to Their Listeners" on the site:
TOM: And with Car Talk celebrating its 25th anniversary on NPR this fall (35th year overall, including our local years at WBUR)…
RAY: …and my brother turning over the birthday odometer to 75, we’ve decided that it’s time to stop and smell the cappuccino.
TOM: So as of October, we’re not going to be recording any more new shows. That’s right, we’re retiring.
RAY: So, we can finally answer the question, if my brother retired, how would he know?
TOM: The good news is that, despite our general incompetence, we actually remembered to hit the “record” button every week for the last 25 years. So we have more than 1,200 programs we’re going to dig into starting this fall, and the series will continue.
RAY: Every week, starting in October, NPR will broadcast a newly assembled Car Talk show, selected from the best material in our archives.
TOM: Sorry, detractors, we’re still going to be on the air!
RAY: But to our fans, don’t be sad. We’ve managed to avoid getting thrown off NPR for 25 years, given out tens of thousands of wrong answers, generated lawsuit threats from innumerable car companies, and had a hell of a lot of fun talking to you guys.
TOM: And when we listen to the stuff that’s in our archives, it still makes us laugh. A lot. We’re hoping to be like “I Love Lucy” and air ten times a day on “NPR at Nite” in 2075.
RAY: Will we change our minds and come back and do some more shows? I would say it’s unlikely, but anything’s possible. Right, Tommy?
TOM: Absolutely not. My brother can go chase himself. I’m done.
From commenters Dingo on the Car Talk blog: "Come on guys! You are part of American Culture! You may as well rip up the Constitution... Now what's going to happen to the Time Space Continuum."