Knocking sound when braking????

[karenw285]

Any ideas. Just replaced front discs and pads on my Astra 1.4 enjoy, and now when I brake at slow speeds (20-30mph) there is a knocking sound. Tried putting a shim behind the disc thinking that the wheel was going on too far and possibly causing the calliper to catch the inside of the alloy wheel. It only seems to be at the passenger side. Bought Mintex discs and pads. Any ideas would be much appreciated. Karen

[paintman]

What makes you think the wheel is hitting the caliper?
Did you compare the old & new items?
Are the pads a good fit in the caliper or loose?
Is the caliper secure on its fixings?

[karenw285]

Just guessing. Tried walking beside car whilst someone else drove and pressed brake. Gonna check old discs with new ones, but as I said think knocking only coming from passenger side.

[Spangles]

Definitely not there before you replaced the pads? Only when braking or when going over bumps as well?

[karenw285]

Knocking not there before changing discs and pads. Only knocks when breaking.

[TheEnd]

Is it a single knock or continuous?
It could be a loose pad, it's not unusual for them to be slightly loose and when they grab, they'll clunk as the hit the calliper.

[Dan67]

What age is it?

[karenw285]

It's a 54 reg astra enjoy. The knock seems in time with each rotation ofthe wheel.

[TheEnd]

OK, the loose pad idea isn't going to be all that is happening if that is the cause.
I'm not sure how the suspension is set up, but there often is some sort of brake reaction bush, this is a bit that will be holding onto the wheel as it forces back against the chassis when braking.
If that is worn, it can make a clunk, but again it would tend to be one clumk per braking event and would have been present before too.

If the brakes are only grabbing the disc at certain points, it'll make multiple clunks. It might even be felt through the wheel as it grabbing to one side.

Possible ways to try and fix it are to take the disc off again and give a light bit of scrubbing to the disc with sandpaper incase there is an oily patch, and also to wire brush the hub it will be mounted on incase a little bit of dirt or corrosion is holding it at an angle.
If you are fitting it with copper grease, only use a very small amount and rub it into the metal. It'll still have a thin greasy film on it, but no gobs of grease that would make it seem warped.

[Locknut]

That sounds to me like the wheel is moving against its bolts.

Have you got after-market alloys?

These often have a spacer ring in the centre bore of the wheel. Different size rings are used to adapt the wheel to the different sizes of hub centres on different cars. If you lost a ring while doing the brakes there will be nothing to centre the wheel and it could move slightly. This might cause a clicking sound with each revolution like you describe.

[karenw285]

Not after market alloys, the car has alloys fitted as standard.

Edited by karenw285 on Monday 6th May 23:37

[PaulKemp]

Check all carrier and caliper bolts, while you've got it apart check all the suspention bolts, then make sure wheel is on properly and wheel nuts/ bolts done up properly in diagonal order

[lee831]

Just a quick one, some pads are directional even though they might look symmetrical.
The pads sometimes have a small arrow on the retaining clips which indicate the direction of travel.
Try swapping the outer (non-piston side) pads round, and see of it goes away.

[karenw285]

Thanks for all your suggestions, going to take brakes apart tomorrow and investigate. Will let you know how I get on.

[karenw285]

Decided to buy another new set of discs and pads (Unipart). Put new parts on offending side only........sorted, no more knocking. Why is this (could it be that the disc was 'out of true'?)

[PaulKemp]

I'm guessing out of true, warped, wrong spigot hole or wheel stud holes to big.