TrevorH

Knocking sound when braking after pads and discs replaced

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Replaced discs and pads all round on my 2013 Grand C-max. No major issues there and all seemed okay. Upon test driving i am getting a knocking sound once per wheel revolution under heavy braking, I have checked the wheel nuts are tight and that the slider pins and carrier bolts are torqued. Could it be the pads just bedding in? Isn't happening on any of the other wheels. Help and advice would be greatly appreciated. The wheel in question is the OSF.

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Can you simulate this by starting the engine whilst that wheel is securely jacked up ( chock other wheels)  ruining the car in gear and then applying the brakes? - probably need an assistant in this job. I have done it looking for driveshaft knocks before.

This way you may be able to pinpoint where exactly the sound is coming from.

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Posted (edited)

The sound is one knock per wheel turn and only under heavy braking so I can only really draw the conclusion that it is disc/pad/caliper related. I am going to double check the bolts and pads etc first. There is no real reason that the noise should be happening if everything is back the way it was before. So frustrating that i took the job on to save a bit of cash (easy job to do really) and it has thrown up a problem straight away

Edited by TrevorH
added info

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25 minutes ago, Hostahousey said:

Could be the pads need to bed in .

Could it be that simple? Also it is only one wheel so why not the other pads as well. If it is a bedding in issue how long would you expect the pads to bed in fully

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Anti rattle springs not seat correctly? Or the disc retaining screw loose allowing disc to move a bit, but having said that ive drilled out that screw and never replaced it with no ill effect.

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I'm going to take the wheel off and just check everything over. Would the anti rattle spring cause a knock? If it isn't quite on correctly would the caliper knock when the brakes are applied heavily? I don't have a disc retaining screw in my discs

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1 hour ago, TrevorH said:

I'm going to take the wheel off and just check everything over. Would the anti rattle spring cause a knock? If it isn't quite on correctly would the caliper knock when the brakes are applied heavily? I don't have a disc retaining screw in my discs

Yes if the caliper wasnt on right it could cause a knock

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2 hours ago, pragmatix said:

Yes if the caliper wasnt on right it could cause a knock

I meant if the spring that sits on the outside of the caliper isn't on properly would that cause a knock?

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6 hours ago, TrevorH said:

I meant if the spring that sits on the outside of the caliper isn't on properly would that cause a knock?

The springs are inside the caliper from memory 

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23 hours ago, TrevorH said:

Could it be that simple? Also it is only one wheel so why not the other pads as well. If it is a bedding in issue how long would you expect the pads to bed in fully

Yes it could be that simple, different wear on the discs . You say it only knocks on hard braking? If car runs ok normal driving I would give it a few more miles, see how it goes.

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9 hours ago, pragmatix said:

The springs are inside the caliper from memory 

There were no springs inside the caliper from the old pads etc. I know the ones you mean though, flattish silver ones that sit inside the tracks that the pads move in and out on. The only springs were on the rear of the inboard pad that grip the inside of the piston. The spring I was talking about is the big one that fits on the outside of the caliper and the carrier. Something like this:

 

https://www.ebay.co.uk/i/233321472676?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=233321472676&targetid=522577504063&device=c&mktype=pla&googleloc=1006861&poi=&campaignid=1782815748&mkgroupid=70885937642&rlsatarget=pla-522577504063&abcId=1139356&merchantid=101452248&gclid=Cj0KCQjwivbsBRDsARIsADyISJ8E_yXuiXXFBzy9E-UuAm_GW5B5ZI9Ae6NUiA9ex-Pu2SsZ5sDkOnsaAlp9EALw_wcB

Obviously not for a Golf but if this isn't put back correctly (it was the hardest of all 4 wheels to reseat) could there be some play causing the knocking?

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37 minutes ago, Hostahousey said:

Yes it could be that simple, different wear on the discs . You say it only knocks on hard braking? If car runs ok normal driving I would give it a few more miles, see how it goes.

Would this just go away on its own then once the disc is a bit more worn? I will see how it goes, but I think I will do a check of everything again with the wheel off to make sure. 

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I had this after replacing discs and pads on my Ranger, and it turned out to be that the bolts that hold the caliper on at the driver side had worked themselves a bit loose, so the caliper was moving slightly when the brakes were applied. 

Bit of red threadlock and plenty of torque sorted it. 

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2 minutes ago, The Finance Guy said:

I had this after replacing discs and pads on my Ranger, and it turned out to be that the bolts that hold the caliper on at the driver side had worked themselves a bit loose, so the caliper was moving slightly when the brakes were applied. 

Bit of red threadlock and plenty of torque sorted it. 

Yeah still haven't had a chance to get the wheel off and check all the torques etc again. I'm hoping that should solve the problem along with double checking the installation of the pads.

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Had everything off and checked and double checked the torques etc but the knock is still there. The outboard pad has a miniscule amount of vertical play and I mean tiny. Could that cause a continuous knock under braking?

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If the pad is moving, then it will knock when braking yes. 

Get that calliper off, check the pads are in correctly and that the pins and retaining clips are all good. 

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When I picked up my previous Focus it had brand new disks & pads and that was knocking about 30% of the time,
I went back to the dealer and he sent me to his garage, took a couple of attempts to get it knocking and they couldn't find anything wrong,
Went back a second time and they were shut, got annoyed and went to my local garage for them to look at it,
After they looked at it and also couldn't find anything wrong, it's never knocked again since!
I assume in their efforts to find a fault they removed something fitted wrong and put it back correctly, a free fix lol.

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On 10/7/2019 at 8:19 AM, TrevorH said:

i am getting a knocking sound once per wheel revolution under heavy braking,

If it really is once per wheel rev, it must be disk related. Most likely a tiny bit of dirt or rust between the disk and hub, making it wobble very slightly as it turns, or some grease or dirt at one point on the disk.

Wear lines on the caliper bracket, which is a wearing part that is rarely checked, will make any slight sideways movement of the pads irregular, and cause a knock sound. If you have the usual Ford single piston caliper, then all of the wheel braking force is between the pad and the bracket. The caliper only provides the clamping (inward) force.

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11 hours ago, Tdci-Peter said:

If it really is once per wheel rev, it must be disk related. Most likely a tiny bit of dirt or rust between the disk and hub, making it wobble very slightly as it turns, or some grease or dirt at one point on the disk.

Wear lines on the caliper bracket, which is a wearing part that is rarely checked, will make any slight sideways movement of the pads irregular, and cause a knock sound. If you have the usual Ford single piston caliper, then all of the wheel braking force is between the pad and the bracket. The caliper only provides the clamping (inward) force.

UPDATE - when we had the wheels off originally we noticed that the wheel nuts were all past their best and agreed that i should change them at some point. The ones on the OSF front wheel (the one with the knock sound) were ruined so I picked up some replacements from Eurocarparts. I have had a closer look and i think that the taper on the bolt is slightly different. They tighten up the wheel sufficiently but perhaps the disc isnt completely snugged up hence the knocking sound. In terms of hardware the nuts are the only different component compared to the other wheels and they are on the wheel that is knocking.

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2 hours ago, TrevorH said:

UPDATE - when we had the wheels off originally we noticed that the wheel nuts were all past their best and agreed that i should change them at some point. The ones on the OSF front wheel (the one with the knock sound) were ruined so I picked up some replacements from Eurocarparts. I have had a closer look and i think that the taper on the bolt is slightly different. They tighten up the wheel sufficiently but perhaps the disc isnt completely snugged up hence the knocking sound. In terms of hardware the nuts are the only different component compared to the other wheels and they are on the wheel that is knocking.

Swop the nuts over and see what happens

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1 hour ago, pragmatix said:

Swop the nuts over and see what happens

That's my next job. Really hoping this sorts it

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So it's not the wheel nuts that were the problem!! Although the Ford ones were a slightly different taper to the eurocarparts ones.

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I still think you should run the car for a while, without hard braking . See if it beds in .

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2 hours ago, Hostahousey said:

I still think you should run the car for a while, without hard braking . See if it beds in .

Sound advice. I drove the car at the weekend and I think the noise is indeed just a bedding in issue as the sound is now a lot quieter and also a lot longer into the travel of the pedal before it happens if at all. In fact, for one journey the sound was not there at all and the pedal felt a lot firmer as well. I was trying to remember if I have ever driven a car with brand new pads and discs before and I don't think I have so certainly a learning experience. Thanks to all the replies and suggestions. What a great forum

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