Grinding noise - but only when it rains????

[mystabe]

I know what you're going to say - sticky caliper :} and it might be! BUT..... it's only started recently, absolutely no noise ever when it's dry but if it rains a 'grinding' noise has started appearing. When you initially push the brake pedal you get a slight initial grinding noise as though the pad is clearing some rust from the disk, however it also happens sometimes when you turn the steering wheel at low speed or go over a speedbump :shrug: It isn't just when you get in the car from parked either - if you start a trip in the dry and it starts raining during the trip it can/will appear again.

I've checked the pads and disks and they look fine and well within spec, the car brakes straight and true there is no noticeable drop in braking efficiency, only happens on the drivers side front and I've checked the spring and damper....... any ideas?

[neilb740]

I get this as well.
I can only really hear it when driving with the window down.
Kind of a quiet scrape, scrape, scrape noise as the wheel rotates.
I never have been able to find the cause and like you my brakes are fine:shrug:

[roverbarmy]

Sometimes, the rust on the outer edge of the disc can raise and just touch the metal on the pad. Carefully clean any rust off the outer edge of the disc and see if that eliminates it.

[andymc]

Could also be the backplates, if they are getting particularly corroded. One of mine was actually slightly bent/warped so that the lower edge was only a millimetre or so from the back of the disc. A flake of rust or a piece of debris could have ended up between the backplate and the hub behind the disc. Trying jacking the car up and rotating the wheel by hand, or even taking the wheel off and rotating the hub by hand to see if you can hear it - maybe even give it a gentle tap to see if anything falls out.

[mystabe]

both valid suggestions ............ but why would there only be any kind of noise when it's wet? :shrug::shrug:

[Dorset Bob]

Dodgy windscreen wipers? :D

[Richard1978]

At the risk of sounding ridiculous, rust does swell when it is wet just like any porous material does when wet and it expands. We are talking about small amounts, but it will contribute. Perhaps the water is getting between friction material and metal body.
Look at your carriers too as the rust may be increasing pressure on pads and stopping them releasing completely.
Get them out clean them up and copper slip where you need to. Sorry it's a bit of an over arching answer, but if you take it apart and put it ago together you will know it isn't fouled up.

[Richard1978]

You can confirm it is brake related by driving and braking at the same time too. If the grinding noise stops when you are pressing the brake pedal, it must be the slider is fouled or the caliper isn't releasing correctly. If it is still present when you are braking it could still be around the circumference of the disk that isn't behind the pads. Don't rule out a bearing either as the grinding may well be unrelated to the brakes.

[mystabe]

At the risk of sounding ridiculous, rust does swell when it is wet just like any porous material does when wet and it expands. We are talking about small amounts, but it will contribute. Perhaps the water is getting between friction material and metal body.
Look at your carriers too as the rust may be increasing pressure on pads and stopping them releasing completely.
Get them out clean them up and copper slip where you need to. Sorry it's a bit of an over arching answer, but if you take it apart and put it ago together you will know it isn't fouled up.

I hadn't considered rust being able to swell tbh - that would explain some things probably. I get the noise when you start pushing the brake pedal but it stops after a second when you've continued pushing. Therefore a combination of swollen rust and a slightly sticking calliper would make a lot of sense.

I know the only answer is to strip the brakes down but I was hoping for a lazy fix :D

Oh and yes Bob - that thought had occurred to me as well but that was easy to check by turning the wipers off and seeing if it still happened ;)

[Richard1978]

Well if it stops when pressed, you most likely have something between pad and disk/ extra friction on the slider preventing pad freeing up when brakes are off / piston not releasing enough.
It might be worth bleeding your caliper and checking fluid level as that could also contribute. But the last idea is a stretch as you have said it brakes as it should so check that last probably haha.

[roverbarmy]

I know the only answer is to strip the brakes down but I was hoping for a lazy fix :D

;)

Just clean the rust off the edge of the disc (I use a light hammer to remove flakey rust and a sander to remove the stubborn rust -lazy fix) before you start doing too much. It's worked for me several times on several vehicles.
Mike

[mystabe]

Just clean the rust off the edge of the disc (I use a light hammer to remove flakey rust and a sander to remove the stubborn rust -lazy fix) before you start doing too much. It's worked for me several times on several vehicles.
Mike

yeah, that was my plan ;) - I do have a new set of pads and disks to go on but I'd rather know what the noise is if possible before I stick them on