Knocking sound after Pads and Disc change

[Trev159]

Changed the pads and discs (all 4 wheels) on my Grand C-max at the weekend. Upon test driving there is a knocking sound (once per wheel revolution) from the driver's side wheel under heavy braking (doesn't occur with just normal braking pressure). I have checked all bolts are torqued, wheel nuts torqued etc but the knocking still occurs. Any ideas what else to try (apart from a different disc or pads)? Thanks in advance

[steveo3002]

wheels off and check again ?

do the pads fit snugly in the carrier...i.e not all sloppy and from the wrong vehicle?

[Trev159]

Pads fit snug and with no movement. I will take the OSF wheel off and have another look. The knocking wasn't there before the change and only happens once per revolution of the wheel so it must be discs/pad related. Either that or I haven't torqued one of the carrier bolts up properly and that is allowing teh carrier to move. Saying that though I would expect that to produce a knock once per braking event, not every wheel revolution. Weird that it only happens under heavy braking though

[Trev159]

If the retainer spring is not quite installed correctly could this allow movement that would cause the knocking? We had trouble getting this one back on easily and the end of the springs that are housed into the caliper looked at more of an acute angle than the other calipers?

[rigga]

Caliper retaining bolt loose, and caliper moving when braking

[Trev159]

I will check all of the bolts again and see if that helps. Could it just be the pads bedding in? Strange that it is just that wheel and not the others

[Coilspring]

Trev159 said:

I will check all of the bolts again and see if that helps. Could it just be the pads bedding in? Strange that it is just that wheel and not the others

Difficult to answer without looking but.

It sounds like either the pads are able to move in the carrier, or the caliper itself is moving, if nothing else has been touched.

[cmsapms]

Mating surface between disc and hub not clean causing disc run out and movement of pads in caliper when clamping the disc?

[Trev159]

cmsapms said:

Mating surface between disc and hub not clean causing disc run out and movement of pads in caliper when clamping the disc?

That could very well be it. When I have the wheel off should I clean the disc as well?

[Coilspring]

cmsapms said:

Mating surface between disc and hub not clean causing disc run out and movement of pads in caliper when clamping the disc?

Quite plausible, and it happens a lot.

But should happen every time grakes are used, not just heavy braking.?

[Trev159]

Coilspring said:

Quite plausible, and it happens a lot.

But should happen every time grakes are used, not just heavy braking.?

Exactly what I thought. Doesn't happen at all with the brakes not applied or with normal braking in traffic conditions. Put a lot of pressure on the pedal and the noise is there. Bloody annoying

[Trev159]

UPDATE - when we were taking the wheels off we noticed that the wheel nuts were probably past there best and that I should replace them in the near future. On the OSF wheel the nuts were totally ruined so we got some replacements from Eurocarparts. I have compared the replacements to the originals and I think that the taper on the bolt is slightly is different. The new nuts are tightening up against the wheel sufficiently (120nm) but maybe not fitting completely snug against the disc allowing it to knock. I am picking up some Ford replacements tonight and will fit them to see if that sorts it. Thats the only difference compared to the other wheels/brakes we changed. I have double and triple checked fitment torques etc and all seems ok.

[PositronicRay]

Some are a straight taper (usually aftermarket alloys) some a radius head.

Make sure yours match the wheel. If knackered they must be running loose or the wrong type fitted.

[GreenV8S]

Trev159 said:

maybe not fitting completely snug against the disc allowing it to knock.

The disc is clamped by the wheel. If the disc is loose, the wheel is too.

[Trev159]

GreenV8S said:

The disc is clamped by the wheel. If the disc is loose, the wheel is too.

It may not be really loose but if the nuts aren't quite the right fitting then there may be some play under heavy load to cause the knock

[steveo3002]

GreenV8S said:

The disc is clamped by the wheel. If the disc is loose, the wheel is too.

what he said ^

[RizzoTheRat]

Trev159 said:

It may not be really loose but if the nuts aren't quite the right fitting then there may be some play under heavy load to cause the knock

If there's enough play for the disk to move there's enough for the wheel to move and you really don't want that!

Check for any marks on the inside of the wheel. I had mine done by a garage some years back and noticed a knocking sound when I went over bumps. Turned out they hadn't put one of the calliper bolts back in and when I went over a bump the front of the calliper was lifting and being smacked back down by the wheel

[Coilspring]

steveo3002 said:

what he said ^

Also what he said.

If the wheel is moving under braking, dont drive it until sorted.

[steveo3002]

check the wheel studs /nuts are the correct length and not bottoming out , also check any replacements are the correct shape theres cone shape and radius ones , aftermarket wheels may not use the same as the factory wheels did

[Trev159]

Thanks for the advice. The noise is a lot quieter after a few more miles of bedding in and the pedal is starting to feel a lot firmer too. Maybe just a bedding in issue that will go away on its own. On a journey in the car yesterday and the sound didn't appear at all. I changed the wheel nuts to Ford ones which were actually cheaper than the Eurocarparts ones so I will change them all round as the old ones are in a poor state. Thanks for all the replies and suggestions. Great forum this