[Pond]

Originally Posted by Ennoch

Discs in this country always wear more heavily on the inside than the outside, especially if you're doing short journeys rather than long as the inside of the disc stays wet for longer, exacerbating corrosion - the outside face will dry more quickly as it's in the sun and isn't protected by the guard as the inside face is. Even on brand new cars you'll find that. Sure, sticky calipers don't help, but they also don't fundamentally change this overall trend.

The delaminating disc surface is one of the reasons I really dislike anything other than blank rotors for street use as it allows rust to creep under. One of the problems too can be if the car is sitting for a while as you end up with polished rust as the braking surface, and rust absorbs moisture whereas actual iron doesn't.

One of the issues with modern cars is that they are overbraked for most driving. Now that's great for emergency stops and when you're really driving it hard because they work well and work for longer, but the downside is that most of the time you're barely tickling the brakes enough to wear the rust off them before you park it up again. And that rust then stays damp, increasing the amount of rust bubbling away, and they never get properly hot to dry because you're not needing to use them hard enough. If you drive big mileages on a daily basis then you'll never really get the same level of surface rust build up but if you drive once a week for example then the rust builds up quickly. It's not down to the discs per se (although some are definitely better than others, as some pads are more corrosive than others), but the design of modern cars with big brakes. My dad has had brand new rear rotors on his Evoque and in 3 months they look like they were never replaced because he doesn't drive hard, lives by the sea, and only does short journeys in the main these days.

May be some truth in that but I have changed many brake discs and NEVER seen ones that look like the pictures above. There is something wrong there and I don't think it is the weather, environment or the make of disc.

[Allworth]

Originally Posted by Eddamoo

Apologies guys I made an error, these are Textar discs/pads.

I honestly feel it's a manufacture issue as opposed to over heating. Both discs are equally bad and the calipers function perfectly. They have been bled well (by me) and have no air. There is no heat discoloration

The front and rears were on the car the same duration in the same conditions but the ventilating fins on the front disc look nearly 5x more corroded on the fronts than the rears. Low carbon steel is more susceptible to corrosion so that's my best guess.

Did I miss something, or you front discs looks corroded ONLY in the inside? Unlike birthday cake which is made layer by layer, whole disc is made from same material as its being poured into a form. One side of your front disc looks fine where the other one is totally destroyed by abrasion and corrosion.
For this sort of abrasion your pads were very excessively engaged,
this level of corrosion could have been boosted by extreme temperatures due to excessive friction of pads with a disc, but only on the inside.
So I see no argument for manufacturing defect of a disc in this case.

[lethbridge]

Originally Posted by Allworth

Did I miss something, or you front discs looks corroded ONLY in the inside? Unlike birthday cake which is made layer by layer, whole disc is made from same material as its being poured into a form. One side of your front disc looks fine where the other one is totally destroyed by abrasion and corrosion.
For this sort of abrasion your pads were very excessively engaged,
this level of corrosion could have been boosted by extreme temperatures due to excessive friction of pads with a disc, but only on the inside.
So I see no argument for manufacturing defect of a disc in this case.

I agree, what seems strange is that the pads in the OP photo look like inner and outer are worn the same - I would expect more wear on inner pad from sticking on guide…

[TurboWeasel]

Looks like the pads haven't worn down uniformly, slightly tapered, which would indicate binding in the caliper carrier.

The inboard side of the disc is in that state because the outboard pads have done most of the work, whilst the inboard side has just rusted away, which Ennoch was spot on about. Exactly the same thing happens with old steel sliding caliper brakes as well.

[Allworth]

Out of interest, can you measure thickness of the disc on both sides - They also look well under the wear limit, especially corroded side.
Btw have you heard of a concept that corrosion is a slow process of burning?

[Eddamoo]

Originally Posted by TurboWeasel

Looks like the pads haven't worn down uniformly, slightly tapered, which would indicate binding in the caliper carrier.

The inboard side of the disc is in that state because the outboard pads have done most of the work, whilst the inboard side has just rusted away, which Ennoch was spot on about. Exactly the same thing happens with old steel sliding caliper brakes as well.

Yeah to be honest the pads were very tight to get out - they needed prying and they definitely weren't 'floating' anymore. The aluminium surface that the pad sits also had some corrosion which looks to have grabbed the pads.

A similar thing happened to our MY20 X4. The corrosion was so bad that the pads 'clicked' as they were applied. It didn't have disc wear like this though.

All that said though, the pads are barely half-worn. Asymmetric wear, whether insiside/outide or upper/lower would surely be significant with that level of disc wear.

I exercised all the pistons with my thumbs and all 4 moved freely and easily with my thumb.

Ill see if i can measure the discs later on. Ill have to use a shim as i only have a vernier caliper.

[Ennoch]

Originally Posted by Eddamoo

Yeah to be honest the pads were very tight to get out - they needed prying and they definitely weren't 'floating' anymore. The aluminium surface that the pad sits also had some corrosion which looks to have grabbed the pads.

A similar thing happened to our MY20 X4. The corrosion was so bad that the pads 'clicked' as they were applied. It didn't have disc wear like this though.

All that said though, the pads are barely half-worn. Asymmetric wear, whether insiside/outide or upper/lower would surely be significant with that level of disc wear.

I exercised all the pistons with my thumbs and all 4 moved freely and easily with my thumb.

Ill see if i can measure the discs later on. Ill have to use a shim as i only have a vernier caliper.

The Brembo OEM caliper design really is crap. Most true race spec calipers, and even a lot of high end performance road aftermarket calipers, use bolted in stainless steel wear plates that the pads sit on so that the pad doesn't dig in to the aluminium, and to help prevent galvanic corrosion between pad and caliper (they usually paint under the plate to prevent that causing issues). Galvanic corrosion is a nightmare on these Brembo things, the lower pad surface on my fronts are pitted and look very much like scrap that's after not that many Scottish winters. I can't see them lasting the life of the car even with rebuilds, and I fully expect that in the next few years I'll be needing to machine them down to then bond on steel surfaces they're so bad. To ensure that mine move freely I've taken a grinder to the folded over tabs on the anti squeal shims to give enough movement. They click from time to time when moving between forwards and reverse but I'd rather that than any binding.

[RickLS7]

This is a common problem with Porsche drilled discs, holes fill with water (especially after washing) and rot the inner face.

Only solution seems to be blowing the water out of the holes with compressed air or not fitting drilled discs.

[Allworth]

Originally Posted by RickLS7

This is a common problem with Porsche drilled discs, holes fill with water (especially after washing) and rot the inner face.

Only solution seems to be blowing the water out of the holes with compressed air or not fitting drilled discs.

I don't know about Porsche discs, but if you examine OP pictures carefully - disc is corroded in many places, and it not typical for any type of discs, vented, non-vented, drilled or non-drilled.
It's overheating due to excessive friction either from stuck pads or a bad caliper.

[peetee]

I've always had issues with judder after a few k miles. Always user Genuine OEM disks and pads

[TurboWeasel]

Originally Posted by Ennoch

The Brembo OEM caliper design really is crap. Most true race spec calipers, and even a lot of high end performance road aftermarket calipers, use bolted in stainless steel wear plates that the pads sit on so that the pad doesn't dig in to the aluminium

Yup. Pretty much every aftermarket caliper I've seen from the likes of AP Racing, Alcon, StopTech, Wilwood etc all use said stainless insert, so I was surprised to see these OEM Brembos have the pads sliding on bare aluminium.

I suppose if the pitting gets really bad, a machine shop could shave the corroded areas down and fashion some kind of stainless pad. The strongest JB weld available might fill in the pitting as a short term fix though.

As you say, shite quality from Brembo there really, given BMW charge about £750 each for the fronts.

Not letting the pads wear down to nothing to minimise sliding and corrosion may also help.

I think because the OEM pads have wrap around shims to slide on the caliper carrier, they could get away with not using stainless inserts.

[Ennoch]

No Brembo OEM caliper, at least on boggo models, comes with wear plates to my knowledge. But all cars with them have issues; Renault Megane 225's have issues with snapped bleed nipples, the Subaru STI/Evo calipers are notorious for stripping the mounting bolt threads, and the nipples seizing too. And the 370mm calipers are even worse at £1200 not £750, as BMW tried to charge when they snapped the bleed nipple off. I just got a local engineering place to fit a Nipple Therapy insert for a total of £75 and we were done. BMW of course 'strongly advised against this'.


I'm really not sure that pad wear levels would really impact it, and having looked at the shim I'd actually suggest the lower surface area compared to just leaving the pad without it would actually contribute to digging in as it's a smaller moving surface than the whole pad edge for the load to push against. It's all minor though, the big issue is that it's unprotected aluminium, mounted to steel and in a salty environment so galvanic corrosion is massively sped up by the electrolyte.

My front left is the worst and is also the one which has now got sticky pistons causing brake drag. I'm going to chance my arm with getting BMW to replace it under warranty but I suspect I'll just end up taking them off myself, repainting and then rebuilding with new seals. It'll be less hassle than the typical arse of dealing with a service manager who tries to tell me the usual lies and bollocks to justify not doing something. I'm certainly not paying £1200 for a new one, that's mental money.

[danb1979]

Going back to my E38 728i in 2010; had the Brembo 4 pot calipers up front

Took me a few weeks to source the parts for my pal to refurb them and even then the bleed nipples were fubar!

Looks like they've never learned!

[TurboWeasel]

Originally Posted by Ennoch

No Brembo OEM caliper, at least on boggo models, comes with wear plates to my knowledge. But all cars with them have issues; Renault Megane 225's have issues with snapped bleed nipples, the Subaru STI/Evo calipers are notorious for stripping the mounting bolt threads, and the nipples seizing too. And the 370mm calipers are even worse at £1200 not £750, as BMW tried to charge when they snapped the bleed nipple off. I just got a local engineering place to fit a Nipple Therapy insert for a total of £75 and we were done. BMW of course 'strongly advised against this'.

Ouch. Maybe I was thinking of the rears. I guess Brembo were the only ones who had enough volume capacity at a price that was right (to BMW). Shame the lower volume brands like AP and Alcon can't do a mass produced OEM caliper. Still, at £1200 each for replacement Brambles, that's a fair chunk into a proper AP or Alcon calipers with a fitting kit.

Originally Posted by Ennoch

I'm really not sure that pad wear levels would really impact it, and having looked at the shim I'd actually suggest the lower surface area compared to just leaving the pad without it would actually contribute to digging in as it's a smaller moving surface than the whole pad edge for the load to push against. It's all minor though, the big issue is that it's unprotected aluminium, mounted to steel and in a salty environment so galvanic corrosion is massively sped up by the electrolyte.

Its just an old habit of mine to reduce piston over extension with sliding calipers. It's still a good practice anyway. I normally bin the pads off once they get down to 4mm or so as they're pretty much done at that point anyway. I'll have another look at the state of mine when the time comes and see what can, if anything, be done about it.

Originally Posted by Ennoch

My front left is the worst and is also the one which has now got sticky pistons causing brake drag. I'm going to chance my arm with getting BMW to replace it under warranty but I suspect I'll just end up taking them off myself, repainting and then rebuilding with new seals. It'll be less hassle than the typical arse of dealing with a service manager who tries to tell me the usual lies and bollocks to justify not doing something. I'm certainly not paying £1200 for a new one, that's mental money.

My car doesn't roll as freely as it should in Neutral, so I might have a bit of brake drag also. Good luck, but I think you know what your chances are!