is it front brake pad knock?

[heptagon]

Hello all

I'm very new here, have had my C7 a few months and have recently had new discs on the front. I am now getting a very loud knocking sound at low speed that seems to be coming from the front right wheel. As soon as I drag the brake pedal it disappears (so hence I think it's pad knock) and I can't detect it at higher speeds (above 20-30mph it seems to stop). I was going to get the car on the stands tonight to have a look, any advice on what to check for? It's a 2002 SV with the ventilated disc/superlight caliper set up.

Thanks

[Irrelevant]

Do you get a pumping sensation through your foot when you apply the brake?

[heptagon]

No pumping. I used to get a lot of judder at low speeds but that was due to a warped disc.

[TeKK]

It's not the wheel hub itself is it? I clattered my Polo against a kerb in the snow and they were worried I'd bent the hub but luckily it's ok.

[Stationary M25 Traveller]

Loud knock !!

 

Are the wheel nuts tightened ??

 

 

..... And the caliper bolts ?

 

PS: welcome to BlatChat.

 

Edited by - Stationary M25 Traveller on 22 Sep 2010 16:11:59

[heptagon]

Thanks, will be checking all these. Not the wheel nuts though, checked those recently.

 

I was expecting it to be something like the pad spring clips or such like but I need to have a look to see what the set up is on these brakes. I will certainly compare one side to the other though for any obvious differences

 

Wanted to have a good look before going back to CC for help. I had pad knock once before on another car after brake pads/discs were changed and that went as mysteriously as it came..

[Mr Locust]

Check for fouling between balance weights and calipers.

 

Ian

 

Green and Silver Roadsport 😬

[Stationary M25 Traveller]

Disc retaining bolts ? Main hub nut/bearing adjustment ?

[heptagon]

ok I have had the wheels off tonight to have a look and nothing seems amiss.

 

However I did find that the outside front right brake pad could be moved fractionally with my finger creating a knocking sound.. the other 3 pads all sit firmly on the disc with no detectable movement.

 

I'm wondering now whether a few high speed stops might resettle the piston back firmly onto the pad?

[Irrelevant]

heptagon: You need to get your knocks, bangs, rattles, etc. correct. Pads rattling around in the caliper is not a "very loud knocking sound "

 

Anyway . . . I suspect your bearings are a little loose. This is allowing the disc to move side to side, knocking the pads back (which does not make a noise) and allowing the pads to rattle in the caliper. IIRC the big brakes have little plates that can corrode or just not do their job of stopping the pads rattling about. When you touch the brakes, the pistons clamp the rattling pads against the disc and the rattling stops.

Easy way or checking front bearings is giving the car a shove with your foot and feeling if the bearings are loose. If they are, tighten them up - it's a 10 minute job.

[OliverSedlacek]

Pad knockback is caused by an out-of-true disc pushing the pad and piston back into the caliper. The most noticeable symptom is that you have to pump the pedal before the pedal firms up, so I'm deducing that you don't have pad knockback.

 

What seems to be your problem is that you have some free play in the up and down direction between the pad and the caliper. At low speed and with no brake pressure the disc picks the pad up, and when it hits the top of the caliper it bounces back down, causing the knocking noise.

 

The pad shouldn't really have any up and down free play. Either your pads are too small, your calipers are worn, or you are missing a spring clip.

[dalongbloke]

I second the bearings idea. Another easy way to check is jack wheel just off the ground, place hands at 3 and 9 occlock and see if there is ANY play or sound.

 

I have just replaced mine at 16,000 miles as one was making a slapping noise, and was indeed quite worn!

 

Applying brakes "pulls" the wheel back against the stub axle and stops any noise.

 

Good luck!

 

Check out Hal... http://picasaweb.google.co.uk/dalongbloke

[Eugene]

Definitely pad up/down knock.

 

Eugene does this too - there is a tad too much up/down free-space on one pad on the front off-side.

 

You don't need a warped disc for this to happen as normal free-play is enough to allow the pad to lightly touch the disc and be pulled up - hence the knocking sound.

 

To be honest, I'm just ignoring it, with the intent to change the calliper some time in the future...

 

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