Brake judder

ABC · Post by **ABC** » 24 Sep 2018, 10:39

Hello

I've got a problem with my XC90 brakes that I can't solve. Started after I had swapped rims for another set of standard alloys( - but that is probably just a coincidence).

Initially felt like a warped disc when braking with uneven pedal feel. (Discs and pads only covered a few thousand miles)

The problem got worse with severe but intermittent judder at fairly low speeds, feeling like OSF (which had a new caliper a couple of years back). Also the ABS light came on and indicated OSF faulty. But it does feel like a mechanical fault rather than ABS operating in error. The car does not pull and normally the brakes are fine and stop the car well.

On inspection there were pad "grip" marks on the disc but all seemed fine.

Changed caliper fixings to avoid play. Even replaced disc retainer grub screw which had snapped when replacing (- but as wheel studs hold disc this should never have been the issue)

I'm now wondering if the problem is NSF?

Has anyone had a similar issue?

Thank you.

Post by **RickHaleParker** » 24 Sep 2018, 23:52

Brake pad clips and retaining springs in place and in good condition?

ABC · Post by **ABC** » 25 Sep 2018, 01:33

Hi

Yes, all good.

Thanks

Post by **oragex** » 25 Sep 2018, 04:55

Osf for US guys means the front left wheel.

If the replacement rims are to blame, the small surface at the wheel hole where the lug is pressed against gets corroded. This corrosion causes greater friction - as opposed with a smooth surface - which affects the tightening torque. The result is an uneven torque on the 5 lugs which deforms the brake disc, causing brake pulsation. Simply clean the corroded surface with some steel wire sponge and tighten the lugs back again - you should feel each lug turns very smooth until it's fully tightened.

Against common sense, I would also recomment tightening the lugs in a clockwise pattern - as opposed to the common cross pattern - but use at least 4 steps to apply the torque.

Also when tightening don't fully lower the wheel to the ground, just enough so it doesn't turn, see this video www.youtube.com/watch?v=cH-f0Q1K5H8

But this would not answer the entire issue the way you describe it being intermittent, the abs light etc. I'm thinking something affected maybe the abs sensor. The pad marks on the disc also cause vibrations - usually cheap pads will dothis.

ABC · Post by **ABC** » 25 Sep 2018, 05:20

That makes sense! Thanks!

This car is proof that coincidences happen so at least this fix should reduce the faults. I’ll be back with an update.

Post by **RickHaleParker** » 25 Sep 2018, 06:22

Have you inspected Strut Mounts and Ball Joints?

ABC · Post by **ABC** » 25 Sep 2018, 06:32

All seems ok there too. The car has had an annoying tapping noise from NS (l/h) for a while so I have a strut top bearing ready to go on, but this seems unrelated as this is an old issue. Thanks