FAQ
TL;DR: Brake discs can reach ~300°C after three 60→0 km/h stops; “it is enough to accelerate to 60 km/h three times.” Light smoke or 124°C readings soon after a pad/disc swap usually point to bedding-in or minor contamination, not failure. [Elektroda, szymitsu21, post #16803104]
Why it matters: This FAQ helps Audi A4 B5 owners diagnose hot brakes, light smoke, and uneven temperatures right after replacing pads/discs, and explains what’s normal vs. what needs fixing.
Quick Facts
- Typical city driving disc temps: approx. 70–100°C after a few minutes. [Elektroda, kkknc, post #16803027]
- New pads reach full effectiveness after about 10 km of use. [Elektroda, ociz, post #16802985]
- 124°C on a rotor is described as a low temperature; smoke can mean contamination. [Elektroda, ociz, post #16802985]
- Initial light pad drag during bedding-in is normal and expected. [Elektroda, Strumien swiadomosci swia, post #16802757]
- Free-moving caliper pistons and clean guide pins are essential after pad/disc work. [Elektroda, moto-kord, post #16802741]
Is ~120–125°C rotor temperature normal right after a pad/disc replacement?
Yes. A single hard stop can generate similar or higher temperatures in a healthy system. 120°C alone is not alarming. Focus on consistent braking feel, no pulling, and equal wheel rotation when lifted. If temps keep climbing without braking, investigate caliper drag or contamination. [Elektroda, szymitsu21, post #16803030]
Why do I see light smoke or smell after my first test drives?
Light smoke often comes from residue or contamination on new discs/pads. The temperature you measured (e.g., ~124°C) was called low, so the smoke likely isn’t from extreme heat. Clean mating surfaces during install and bed the pads correctly to burn off residues. If smoke persists after bedding, recheck for grease or fluid on friction surfaces. [Elektroda, ociz, post #16802985]
How long until new pads ‘bed in’ and stop feeling weak or grabby?
A fresh set should reach full efficiency after about 10 km. During bedding, slight drag and mild odor can occur but should diminish quickly. Avoid long, continuous braking on the first few drives; use several moderate stops from safe speeds. Verify smooth pedal feel and no wheel lockups. [Elektroda, ociz, post #16802985]
What rotor temperatures should I expect in city driving?
Typical city use brings discs to roughly 70–100°C within a few minutes. Short stops and lower speeds keep temps in this range. Longer descents or repeated hard stops will push temperatures higher. Monitor for symmetry side-to-side; large persistent differences suggest drag or contamination. [Elektroda, kkknc, post #16803027]
Why do brake temperatures rise so fast?
Brakes convert kinetic energy into heat. As one expert put it: “When you use the brakes, the temperature rises.” Repeated decelerations stack heat faster than the system can shed it, especially with limited airflow. Plan cool-down coasts between hard stops when testing new pads. [Elektroda, kkknc, post #16802783]
One wheel reads hotter than the other—what should I check first?
Start with clean, dry friction surfaces. If you see smoke, pads or rotors may be contaminated. Confirm the caliper slides freely and the piston retracts smoothly. Unequal temps after equal driving usually mean drag on the hotter side. Address contamination or sticking hardware before further testing. [Elektroda, ociz, post #16802985]
Should the wheel spin completely free after installing new pads?
Expect slight resistance at first. New pads need to ‘arrive’ (bed to the rotor surface). A light, even drag that reduces after several drives is normal. Persistent heavy drag or a wheel that’s hard to turn indicates sticking slides, twisted hose, or a seized piston. [Elektroda, Strumien swiadomosci swia, post #16802757]
Could a nearly fully extended piston corrode and then stick afterward?
Yes. If a piston spent time near its travel limit, corrosion can form beyond the usual sweep and later cause sticking. This presents as hot brakes, uneven temps, or a dragging wheel. Inspect boots, piston finish, and retraction. Replace or rebuild if pitting is present. [Elektroda, 1098678, post #16803011]
How do I check for sticking guide pins or a lazy caliper piston (3 steps)?
- Lift and spin the wheel; compare resistance side-to-side.
- Remove the caliper; verify pins are clean, straight, and greased correctly.
- Retract the piston; it should move back smoothly and evenly without force spikes. [Elektroda, moto-kord, post #16802741]
What is the caliper yoke, and should it have holes?
The yoke (carrier) holds the pads and guide pins. Inspect it for proper hardware, clear passages, and no blocked holes or burrs. A dirty or damaged yoke can cause pad hang-up and heat. Clean the carrier and ensure pads slide freely in their channels. [Elektroda, Strumien swiadomosci swia, post #16802757]
Are my install steps OK if the piston didn’t retract easily at first?
The piston should retract easily and evenly. If it resists, stop and address dirt, corrosion, or misalignment. Forcing it risks seal damage and future drag. After cleaning guides and confirming smooth piston movement, reassemble and perform a controlled bedding sequence. [Elektroda, moto-kord, post #16802741]
How hot is too hot on a long downhill or repeated hard stops?
Sustained braking on descents or repeated 60→0 km/h stops can drive discs toward 250–300°C. Reserve gears and intermittent braking help control heat. If you feel fade, lengthen cool-downs and inspect pads for glazing before continuing aggressive use. [Elektroda, szymitsu21, post #16803104]
Which brands were mentioned, and do brands change rotor temperatures?
The thread mentions Ferodo shields and Delpchi pads. Initial heat and light smoke relate more to bedding, cleanliness, and free-moving calipers than brand choice. Verify correct installation and condition first; then evaluate pad compound if issues persist. [Elektroda, 1098678, post #16802719]
