Car Clinic: Brake Failure Not From Tyre Change

Car Clinic: Brake Failure Not From Tyre Change
 

Question:

I recently fitted new tyres to my 2006 Renault Clio to replace the previous ones. Since fitting the new tyres, I have from time to time experienced brake failure, and as a result have already been involved in a fender bender. The brake pedal just goes down, followed by the sound of a terrifying vibration, which can also be felt on the pedal. It normally happens after the car has been driven for a while. The brake discs and pads have already been replaced, to no avail. What could be causing the problem? The tyres perhaps?

—Ronald

Answers:

This is a baffling case, Ronald, but I’m reasonably sure that the tyres are not to blame — it’s a brake problem, not a tyre problem. Further than that, we can only speculate. Something must have happened during the tyre change to cause the brake malfunction, something that wasn’t corrected by fitting new discs and pads. The first conundrum is whether it’s ABS – related or not.

It is possible that a wheel speed-sensor was knocked out of position during the tyre change, and is now supplying duff information to the control unit, causing the ABS to intervene when it should not. If we assume ABS is not involved, worn wheel bearings enter the picture. This can cause symptoms similar to what you describe, but we have to accept the coincidence that the wheel bearings became critically sick at exactly the time when the tyres were replaced.

I spoke to a Renault mechanic who considered a faulty brake booster the most likely suspect, but once again, why did it suddenly pack up when the tyres were replaced? A brake calliper not moving freely on it guide pins is also a possibility, and that can happen if a guide pin is bent, but the calipers are not normally disturbed during a tyre change.

I suggest you check for a displaced wheel speed sensor, feel for play in the wheel bearings, examine the vacuum lines to the booster, and finally give the callipers a comprehensive service.

-For all you motoring queries, please contact Gerrit Burger: geb@mweb.co.za