QOTW #32 – Carbon Ceramic Brake Noise on My Aston?

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Welcome to Bamford Rose and another question of the week. This week, it’s abnormal noises among Carbon Ceramic Brakes. We have here a completely worn out destroyed disk. We have here a completely brand-new never feed to a car disk. So, the first time for noise you could get and if you bought the car and it already had the disc brakes fitted and it was quite some time ago and it’s got this particular type of noise. Then it could have this noise even though that period of time it’s quite long. This will be because the brakes have probably never been bedded in probably. And it’s difficult for a new disc not to be bedded in, because you can only buy a new disc from the factory pre-bedded to the pad. So, you get a pair of pads and a disc.

But if you’re changing pads halfway through disc wear, because the pads are low but the disc is fine. Then the pads need to be bedded in and this quite difficult cycle needed to bed pads improperly. If you gradually take the disc up to temperature and then arduously use the brakes to the point of brake fade in a controlled way without temperatures spiking too quickly the assembly, then no matter what procedure is specified that’s good enough. So, to get brake feeding on Carbon Ceramic Brakes is extremely difficult. It’s going to take in a number of accelerations up to speed and deceleration bowing down again. And keep doing and keep doing until the point on that final cycle we put the brakes on and you’ve got no brakes whatsoever is complete brake fade.

At that point, the brakes are bedded in. It’s a new assembly. You get smoke coming out of all four corners and you get this smell like TCP. That’s the chemical reaction of the bedding in a process that sets about a transfer layer between the pad and the disk. So, because of squealing and often accompanied by poor brake performance, it’s going to be improperly bedded. Now when these are installed in the caliper, you probably see there that there’s some whiting of the edge where the pad would be touching the disc. That’s indicative that the pad is bedded improperly, because you get that white witness mark when the pads have been up to sufficient temperature.

If you’re looking at discs and they’ve got none of that aging around the outside, chances are the pad is not bedded in probably. What that is probably accompanied with, because this system isn’t working properly. It’s a rough to touch surface of the disc. So, really the disc should be a mirror to touch very smoothly. And if the assembly needs a new bedding in process, then as you probably see from this disc it’s extremely rough. You can almost hear the glove picking up on the surface where there should be a mirror and you hear none of the sort of grating sound. So, that’s probably accompanied as well if it’s whistling with a real gravelly type sound instead of the normal air gush type sound you get when everything is good. So, squeal for pads that aren’t bedded in properly or the disk is too rough.

The next will be squealing just because it’s a fresh pad on a new disc and the disc has got some wear characteristics. Which causes the path to contact and whistle against and this is a perennial problem. There are numerous problems really with Carbon Ceramic Brakes and it’s why on new cars the factory reverted back to Steel. Obviously for marketing for styling these are very good, but practically they’re quite difficult things to live with especially if you have to fix them, because it’s very expensive things to fix. So, in the case of squealing, then you wouldn’t be getting the gravelly type sound and the disc would probably look or feel the mirror to touch.

It’s possible to make a chamfer on the leading edge of the pad make a chamfer and then there are some empty squeal compounds that will go on the back of the pad. I’m not a fan of those, but that is a factory service bulletin. The next type of noise, I wouldn’t say this is a squealing noise but anything is possible. This is where the Phosphor Bronze pins that mount the pad into the backing plane, we’re through and this set is exactly at that point in time. And the point in which the pins rub through is actually before the wear indicator would come on.

So, when the pins started to rub through probably when the factory was developing this, they thought that pins protruding and rubbing on the disk wouldn’t be a problem. But after years of heats cycling, those pins are gone quite hard. Now the pins protruding through causes a problem you often get a circular sort of wear mark around the circumference. You can often hear that as the locating pin is acting against these cooling holes. I’ve never heard that as a squealing. So, those are the types of sounds that you can get from these brakes, and what the typical causes are. If you look into buying a car or you have got a car and it’s got some abnormal noises efficiencies a bit poor, the best thing you can do is run it through a thermal reconditioning cycle. Get the brakes really really hot, and that will help create a transfer layer between the disk and the pad.

Try and return a disk with a rough surface back to the mirror to touch the surface. Hopefully improve efficiency and get rid of noise. But getting to the bottom of a squealing noise can be a real pain. Sometimes you repair, replace everything, put leading edges on the pads, put some compound anti squeal compound on the back of the pad and never going to alter the squealing. Root cause is more likely the disc and obviously, it’s very expensive to replace a disc when there’s some wear left in it. Could be cases where the pad is loose, maybe in the caliper that’s moving around a bit. But each car is different that needs an examiner.

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