Vibration through brake pedal

[barchetta]

Hi all, 

Over the past 12 months vibration through the brake pedal has got worse. We’ve had new tyres, pads, discs last week and still no better, checked sliders, pistons seem to be free moving in and out. Changed rear pads too, still vibration felt over 30mph, up to 70mph the car feels as if the disc was warped or something. when wheels off the ground run up to 70mph, 140 through one wheel and stamp on the brakes and nothing. I’ve had a look at tighten bolts thinking these might not be holding the calliper correctly, seems from the left front but at this point not sure what to try next. Any thoughts gratefully appreciated.

[paul9]

I would get my wheels balanced before looking further into the problem. Then I would have a look into the ABS pump/system. That said, your wheels should have been balanced with the new tyres, so if you had them all changed, those shouldn't be the cause of your problem.

[Duggerz]

Hello barchetta,

You've replaced the discs and pads and yet you described continued vibration under braking only which would tend to suggest it's not a wheel balance issue. If you discount the new discs being warped, that leaves you with a problem with one or both drive flanges. These flanges can accumulate festerage which might cause the symptom you described, and before the new discs were fitted they should have been cleaned thoroughly and there should be no lumps or bumps on the mating surface. If they are clean and flat, then I suggest getting a DTI on them and checking that the run-out is within tolerance. I'm assuming the wheel bearings and steering joints are all good. Hope this helps.

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[barchetta]

We changed the wheel bearing two years ago, no play in the wheel. It is only under braking and that is why I’m at a loss. It doesn’t vibrate under acceleration or whilst driving along. Flange looked clean when replacing the disc. 

Thanks for the comments though.

[Duggerz]

It's worth running some abrasive over the flanges and checking for run out with a DTI though. And while you're at it, check the run out on the new discs which I think you can do by spinning on the nuts without the wheel maybe with some washers just to nip them to the flanges.

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