I was going to replace it in my car at 90,000 miles but after removing the old ones I found they were in very good condition. The factory recommends a replacement at 150,000 miles, but check every 10,000 after 100,000 miles, so I decided to keep the old one and wait until it showed signs of major failure - usually the slip makes a high-pitched noise before failing. Big fan of Ford and Motorcraft parts because they make honest, no-fuss parts of great quality and durability at a very reasonable price - even lower than most parts.