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Old 10-03-2017, 11:06   #1
heaveho
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Squeaky Carbotechs, but not when braking

So, my front brake setup, which had previously become troublesome ( judder ) on DS2500s and nearly worn out AP discs, was fixed by a wheel alignment ( yeah, don't ask me, I don't make the rules ), but only after significant expenditure on admittedly necessary new discs and possibly unnecessary but excellent new pads, so my new front brake setup ( 330 PF discs, AP 6 pots, Carbotech XP8 pads ) stops the car quickly, quietly, without fuss.

It seems the new pads however, having decided not to make any noise under braking, constantly squeak when the car's moving, which is almost worse. Nothing's stuck or seized, the car doesn't pull one way or the other, whether under braking or not. The squeak actually stops when the brakes are applied, so the absolute opposite of the usual Carbotech problem!

Is this a common thing with these pads, never had it in the previous 12 years of other pads?

Last edited by heaveho; 10-03-2017 at 11:07..
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Old 10-03-2017, 11:15   #2
thetyrant
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Is there a lip at all on the disc ? only takes a very small lip and the pads just touch it when not braking which can give this kind of noise, also check the pads are nice and free to float in the caliper as again any slight resistance preventing the pads knocking back from disc face when you come off the pedal again causes this sort of noise.

I would say first thing is a mini brake service and inspection, get pads out give friction faces a good scuff over with coarse p40 etc paper to break up any glaze build up, clean out any brake crud in the groove and rivet holes in friction material, give backs of pads a clean to remove any old hardened copperslip etc and same inside caliper, once all clean give the ends of pad backplate as very thin smear of copper slip and same where pistons touch pad then refit.

Check disc carefully while pads our out for lips and any build up of glaze etc on them, again a good scuff over with coarse paper to clean surface, if there is a small lip then you can file edges of pad friction to clear it and that will sort it.

See how that goes usually helps quieten it down, would also be interesting to see what your disc runout is with a dial gauge if you have one ?

Ian
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Old 10-03-2017, 14:12   #3
heaveho
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Thanks Ian, I'll be having a poke around it soon before it goes to Scotland, so I'll follow all of that advice.

Don't have a dial gauge, however the discs haven't done many miles, the pads have only done hundreds, not thousands of miles, and there is now absolutely no judder, so if there's runout of any significance, I'd be surprised. The brakes feel really sharp now.

I did maybe 30 laps at Croft in August, but they were doing it before then, so I doubt I can even blame that. Hadn't driven it for nearly a year before that, and drove it the day before yesterday for the first time since.

Thanks for the reply.
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Old 10-03-2017, 16:22   #4
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Make sure you haven't got a sticky piston
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Old 10-03-2017, 17:32   #5
heaveho
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Make sure you haven't got a sticky piston
Thanks, it's on the list! Along with loads of other things.......
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Old 13-03-2017, 19:51   #6
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Ok, annoying result for an hour and a half of work.

Before stripdown, absolutely nothing wrong visually, or at the pedal. Just the squeak, consistent with the rotation of the wheel. No lip whatsoever on the disc, barely any corrosion on the vented edge. Grooves in the discs were clean. The discs were then given a scuff off with rough sandpaper. Pads levered back easily.

Pads out, no lips, very slight cracking in the face, very slight signs of the edge of the pad starting to come away from the backing plate. Nowt I'm bothered about as it stands, seen worse without issue. They've done ( much ) less than 1000 miles on the road and one trackday. No noticeable dust build up, and the slot in the pad was clean. The pads had the edges chamfered when fitted, I re-did this anyway. I also put a V in the slot to take away the sharp edges. Then faced them on a flat block. Then cleared the dust I'd created from them.

The insides of the directional anti squeal shims and the holders
( AP330s ) were corroded. Cleaned back to bright metal and given a light covering of copper grease. The shims the pads sit on weren't bad, again, cleaned and given a smear of copper grease.

The pistons move freely and show no signs of sticking. Pads dropped in easily after having the backing plates thoroughly cleaned and greased along with the mating edges.

Put it all back together, pumped the pedal and drove it. Did several miles with a few light stops out of necessity while driving out of the city centre I live in. All good at this point, no squeal on or off the brakes. Got onto a quiet dual carriageway and did a few several hard stops. Brakes feel very strong, the back end of the car goes light enough to make the car squirm. No judder.

No squeal under braking during this, but the rotational squeal afterwards when they aren't being applied is perhaps 10 times worse now than it was before! So tomorrow, I'll be trying the old DS2500s I had fitted previously. Can't live with that racket!
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Old 13-03-2017, 20:04   #7
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Leave them in and do a few more miles with some harder braking see if it settles, the squeak with rotation is the disc just catching the pad at a high point in runout and why I was curious what it measured, it must be minimal or you would have vibration under braking but its obviously not zero or the squeak would be all the time or not at all.

As said do another session on it see if it settles down, the fact you have made it worse is odd mind!

Ian
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Old 13-03-2017, 20:37   #8
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As said do another session on it see if it settles down, the fact you have made it worse is odd mind!

Ian
Aye, it's a bit weird. It's from both sides now, not just the drivers, and it's loud enough to hear with music on in the car! The car rolls freely, there's nothing stuck on.

I'll try it again, but I can't be going away in it with that happening, it's just too much. I was applying the brakes just to make the noise stop when I was out in it earlier!
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Old 13-03-2017, 20:51   #9
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On front brakes I would always check the runout numbers- as thetyrant suggests.

Do you know if the discs went back on in exactly the same positions as previously?
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Old 13-03-2017, 20:57   #10
heaveho
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On front brakes I would always check the runout numbers- as thetyrant suggests.

Do you know if the discs went back on in exactly the same positions as previously?
Hi, yeah, I marked them before they came off. I'll see if I can get hold of a dial gauge, but I'll try the other pads first, they're here, and it's a quick swap.
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Old 13-03-2017, 20:57   #11
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With carbotech, I get them hotter and hotter to the point of steaming/on fire. .... Then allow to totally cool.

Works for me every time.
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Old 14-03-2017, 13:54   #12
heaveho
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Well. thought I'd found the problem.....noticed a score mark around the edge of the bell on the disc, and the pad looked very close to it. Comparing the Carbotech to the DS2500, the Ferodo is noticeably further away. So I spent about half an hour grinding the pads back to give more clearance around the bells.

Convinced I'd solved it. I haven't!
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Old 16-03-2017, 17:09   #13
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Have used the XP8s and 10s.... to stop the 8 making a noise bean the brakes on and get them smoking , but I got some XP10s and they are as quiet as a mouse .
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Old 17-03-2017, 08:28   #14
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I'd say there seems to be no rhyme or reason as to when and why the XP8s squeak lol
I've had them in standard brembos on a VI and they made horrible noise both braking and when not braking, caned them on the track and made it worse, then sometimes they'd be silent for no reason
Currently got them in AP 6pots on my extreme and they're silent, but previous set i had in the same AP 6pots were quite noisy even when just driving along, again no real reason, didn't do anything different with the current set compared with previous etc

Basically, I am of no help because I can't work them out, i'm just glad they're silent at the moment LOL
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Old 17-03-2017, 13:28   #15
heaveho
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I'd say there seems to be no rhyme or reason as to when and why the XP8s squeak lol
I've had them in standard brembos on a VI and they made horrible noise both braking and when not braking, caned them on the track and made it worse, then sometimes they'd be silent for no reason
Currently got them in AP 6pots on my extreme and they're silent, but previous set i had in the same AP 6pots were quite noisy even when just driving along, again no real reason, didn't do anything different with the current set compared with previous etc

Basically, I am of no help because I can't work them out, i'm just glad they're silent at the moment LOL
If I hadn't already had a good look, I'd have said there's something caught between the disc and backing plate, it's constant and loud......except when braking.
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