Brakes Knocking?

[RichRSi]

Dont know how best to exsplain this; every now and then when braking gently at low speed (around 15mph) I get a knocking sound that I can also feel through the pedal. No warning lights show on the dash btw.

It only happens every 100 or so miles then nothing for weeks. Braking is not effected at all (even with the noise) infact the brakes are better than my folks brand new Swift.

I took it to a french car specialist garage and they checked it over on the diagnostics, they road tested it also, he said "no problems with it at all, could be a very very slight warp in the disks but your brakes dont need replacing as they are 100%"
I spoke to a main Renault dealer who suggested that the ABS will do a 'test' when you apply the brakes every now and then as part of a self diagnostics to check operation is good, if all is not good you get a failure light, then they asked if I had a failure light on, which I dont. They wanted to charge nearly £60 for plugging the thing into the same bit of equipment the last guy did.

Just incase it was the tyres (about 4-5mm left) I bought brand new Pirrelli's for the front.
Pads and disks on front were renewed about 10k ago and there is plenty of meat on them all round. The drums :S on the rear are also fine.

The knocking still some times happens, a third opinion anyone?
anyone had a similar thing?

 

[GeG]

I've been experiencing the same problem on my 172 for a few months now. It started off happeing every now and then but has recently become alot more consistent. Does anyone know what this is?

 

[RichRSi]

I've figured this out to be the ABS activating under light braking and grown to live with it. I have the same problem as you, in that it has become more consistant with time.
It seems to happen mostly when doing about 10mph stopping for some lights. The ABS works fine in all situations when you would want it to as I found out when a van crossed my path without warning the other day.

I can only think that there maybe a fault with one of the units that sends a message to the ABS to activate (seeing as the system actually works) irc there is a sensor for each wheel (but I have rear drums so dont know if these also have a sensor each)

The car just passed an MOT (and the brake test) and he even commented on how good the brakes / condition of the car was.
At the next service I'll get the brake fluid renewed, as the problem started soon after I had new disks, pads and fluid, perhaps there is a 'worm' of air in the system.

 

[Laura Fletcher]

ive had this but tried to ignore it. Had it checked and non-conclusive also. Its at a very slow crawling pace that it happens :rasp:

 

[Shindig]

a stone between the discs and pads?

forget what i typed, i read the above posts properly

 

[GeG]

Strange... I started to notice the problem after having the brake fluid replaced and new front pads put on too.

 

[gtruk]

same issue here....happens low speeds. Cleaned all sensors with dry paper towel and cleaned all abs rings/notches...problem persists. Maybe will have to live with is?

 

[Hegs]

is it the front or bak wer the knokin cums from?

 

[deviltronics]

are you sure its not the brakes pads knocking inside the caliper. the springs that hold them tight maybe squashed to much.

so when you brake and then come off the pedal they whack the inner caliper housing due to the opposing forces.

if you know what i mean..........

 

[gtruk]

Not in my case deviltronics. If it was just a knocking noise then sure, id almost agree with you....but you can distinctivley feel ABS when it kicks in as like a taptaptaptap on the brake pedal.

But you might be right in other cases....I think its something ill just have to bare with until it gets worse.

 

[Jimzar]

I have the same problem. Started after a all round disc and pad change. No idea what it is, but some times i get the ABS, ESP and SERV light come on too!! going to get put it in to get looked at in a couple af weeks.

 

[richard2k84]

I have the same thing with mine. My mate said its jsut the ABS. It does it every now and then and its nothing to worry about. I trust becasue he is a mechanic. So just thought i would let you know

 

[Jimzar]

It would be ok if it was just every now and then but mine does it almost every time I slowly brake for traffic lights or something like that.

 

[richard2k84]

Well i would check the usual suspects like pads, disc's arent bent or chipped. Maybe check wheel bearings. Sorry thats all i can think of

 

[Jimzar]

Na iv checked all of them it all seems to be ok!

 

[H182]

Had this problem in my old car, turned out the ABS rings were cracked. Got them replaced and all was good.

 

[Jimzar]

Could you get this done at most garages?

 

[gtruk]

how would a cracked abs ring affect the frequency the sensor reads? The ring is a series of notches.....if one of the notches was missing id understand...

 

[H182]

Maybe it was further apart then it should have been where it was cracked causing inacuracy, unless one of the notches had cracked off. Dunno really but it fixed it once I got them replaced.