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I have a 2008 Yaris T3. It's been serviced regularly, and at the last service the brakes (front and hand brake discs) were checked, and skimmed. That was about 4 months ago. About two weeks ago, something started happening when I braked for the first (or sometimes) second time during a trip, but only intermittently. There was a knocking feeling (no sound initially) on the brake pedal, two to four shudders that feel like someone is hitting pedal lightly with a hammer from underneath. My ABS light would come on for a couple of minutes, then turn off. The brakes don't feel different, and the rest of the trip no matter how long, would be fine. It's more common on cooler mornings, but not exclusive to them. From limited testing, it happens during equally on slow/easy stops and fast/hard stops.

I booked the car into a mechanic, but with the pre-holiday queues, I had to wait another week. During that week, whatever was happening started making a noise too. The knocking feeling is accompanied by a knocking sound and the "ping" of a large spring releasing (you that "boing" sound?) The mechanic, inspected the brakes, but he couldn't find anything. The ABS reported some minor issues which he attended to, dirty sensor, loose connection, and he told me my clutch was on the way out, but would last another 6 months or so.

My thoughts are that it could possibly be

  • the brakes because it happens when I brake
  • The CV joints because of the spring sound
  • The shock absorbers/suspension because of the spring sound

Searching initially yielded this possibly similar question: Banging sounds coming in front of my car

Is it possible that a loose torque plate bolt is the problem? I have the car booked in for tomorrow morning again, but I'm struggling to describe the symptoms to the mechanic. I was hoping some of you fine folks might have had a similar problem and could point me (and thence my mechanic) to the cause of the problem.

  • Interesting question. I think some of your listed possibilities have some merit. – DucatiKiller Dec 14 '15 at 18:07
  • Does the 'boing' sound happen every time you experience the braking problem? – HandyHowie Dec 22 '15 at 18:14
  • @sirlark were any of the responses helpful? – DucatiKiller Dec 23 '15 at 0:43
  • @handyhowie initially no, but now yes, every time – sirlark Dec 23 '15 at 6:23
  • @ducatikiller yes, but I'm not sure which one is the correct answer yet, and the mechanics are all closed till after new year – sirlark Dec 23 '15 at 6:25
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If the ABS light will turn on every time the you feel the shudder in the brake pedal, then the ABS braking is being actuated. This could be caused by a tire skidding or the ABS computer thinking a wheel is skidding. The wheel speed sensors report the speed of each wheel to the ABS which determines if the car is skidding. You mentioned that it happens on slow/easy stops. I would said a wheel sensor is reporting that a wheel has stopped even though the wheel is still turning. One of the wheel speed sensors is probably damaged. Yaris forums report a lot of problems with the rear wheel speed sensors.

  • Can you explain what you mean by 'actuated' please – sirlark Dec 17 '15 at 19:50
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    It seems it was combo of both your answer and @HandyHowie's. Between a worn wheel bearing and faulty ABS sensor, the ABS was actuating on my other wheel. – sirlark Mar 16 '16 at 14:45
  • Same conclusion in my problem - when I press the brakes too hard ABS starts to work and I hear the same sounds. Any advice how to fix it? – Jack Spektor Mar 30 '17 at 4:18
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Seems like a bad brake caliper piston. When they start to go bad they tend to "stick". Sticking means that the piston inside the caliper is not freely sliding in and out when pressing against the brake pads. The sound you hear could be the caliper freeing itself from the stuck position. The springs sound could also be related because your car uses metal shims (that act like springs) to hold the brake pad in place.

This is a safety issue. Take it to your mechanic and have him inspect the calipers by removing the pads and pumping the brakes. Any damage will be obvious.

The caliper can be rebuilt at a lower cost. Toyota sells an affordable repair kit. The mechanic might recommend a new caliper because its easier for him to replace. Your choice.

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    Thank you for your answer. My mechanic went over the brakes again but found nothing wrong, but the ABS was still reporting errors through the car computer. His theory is that the ABS unit itself is faulty, and not releasing my brakes properly. Is this likely? The ABS light has been giving false alarms for some years – sirlark Dec 16 '15 at 5:09
  • @sirlark Yes, it is a likely problem. The ABS unit is mechanical and does wear out. :) – race fever Dec 17 '15 at 17:37
  • This a great answer. Next level. – DucatiKiller Dec 23 '15 at 0:42
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I have experienced a similar fault on a car where the ABS would come on unexpectedly. This turned out to be a worn wheel bearing which was allowing the gap between the reluctor ring and the abs sensor to vary slightly, which confused the ABS. It was some time before any other symptoms of a worn bearing became noticeable.

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