When you describe brake pedal vibration on the first stop, followed by the ABS light coming on, then it resets after a restart, that almost always points to the ABS system getting a bad wheel speed signal. Here’s what’s happening on your F-150: --- 🔎 What’s Going On When you first braked, the ABS module thought one wheel was locking up (because its sensor wasn’t reading correctly). It pulsed the brakes (what you felt as vibration). Then it “realized” the signal was faulty → triggered the ABS light and shut down the system. When you restart, the system resets — until the bad sensor/wiring acts up again. --- 🚨 Likely Culprit Bad or intermittent front wheel speed sensor (passenger side very likely since work was just done there). Damaged or loose wiring/connector — could have been disturbed during your exhaust manifold replacement. Rusty or cracked tone ring (the toothed ring the sensor reads) — very common on older F-150 hubs. Rust builds up under the ring, making the sensor misread. --- 🛠️ What You Should Do Next 1. Check the passenger front sensor and wiring first (as we mapped out earlier). Look for rubbed/melted insulation near the manifold, or a loose connector at the frame rail. 2. Inspect the tone ring (reluctor) on that hub. If it’s cracked, rusty, or missing teeth, that’s your problem. 3. Scan ABS codes with a scanner that reads ABS (parts stores like AutoZone can usually do this for free). It will almost always say something like “Right Front Wheel Speed Sensor Circuit Intermittent” if that’s the culprit. --- ✅ Bottom Line Your base brakes are fine (no fluid or hydraulic issue). This is 100% an ABS electrical/sensor issue, not the master cylinder or booster. Most likely: passenger front wheel speed sensor or harness, given the timing with the manifold job.