When does a brake disk *really* have to be replaced?

Bmachine

Bmachine

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My disks look very good. Perfectly smooth, no groves, no lip. Looks like there is plenty of meat left on them as well.

But when I put the (measuring) calipers to them, they show 20mm in thickness. This is below the 21mm minimum required as per

http://www.e9-driven.com/Public/Library/BMW-E9-Manual/PDF/D\e9_34e.pdf

The rears are 18mm. So that one is at the minimum of 18mm.

They may be looking so good bc someone turned them not too long ago. But I wonder if every one puts on new disks as soon as they hit 21mm.... That is a (yet another) $600 parts bill so I wonder what others may have experienced.

Thank you

Bo
 
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I'd run them. With less mass, you may be able to make 1970's pads fade sooner than you could before, you may be able to make 1970's spec brake fluid boil sooner than before. Basically the manufacturer has no control over what happens below that thickness and doesn't want to be responsible for it. But I've seen rotors worn clean through into the air channels without coming apart, so I would not worry about a catastrophic disc failure.
 
Wow Don. That is an amazing price. The 4 corners on WN are about $600 w shipping. I'm always real skeptical about buying critical parts on ebay.

Are those Centric ones decent quality? Has anyone tried them?


Sent from my iPhone using Tapatalk
 
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On all my BMWs, I don't try to save money on either brakes or tires. I get rid of my tires before they are completely worn out and I change brake components before they are completely worn out. I sleep better that way.
 
My understanding is that there's a bigger chance of the rotor warping as it gets thinner. More heat with less material, which could cause it to warp, or in extreme cases, heat up so bad that they crack. Cracking isn't likely unless you're on the track or running them very hard. I've never measured any of my rotors and replace them if they start warping or just don't look right. Pretty scientific eh?
 
Bo,

I have had some 'problems' with centric rotors being 'out of plane', causing steering wheel vibration when on the front and brake pulsation when on the rear. I am partial to Zimmerman as an aftermarket brake rotor supplier. Used lots of them on my Porsches - both for track driving and for street driving. Just my experience.
 
Thanks very much for the great feedback and info guys. Super helpful.

For what it's worth, here is a thread on the subject from Bimmerforums:

http://www.bimmerforums.com/forum/showthread.php?1807938-Centric-Rotors

The impression I am getting is that reviews are mostly positive as long as you keep in mind that, as with everything, when you go for a cheaper product, there will be greater variation in quality control and there is (small) chance you might end up with an item that is not up to par.

Gary, where do you get your Zimmermans from?
 
My friend just bought a 733i with brake issues for $150. The attached photo shows that perhaps the time to replace the rotor has passed.
Worn through, he said.
The rest of the car is in surprisingly good condition.

Ian
 

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mulberryworks said:
My friend just bought a 733i with brake issues for $150. The attached photo shows that perhaps the time to replace the rotor has passed.
Worn through, he said.
The rest of the car is in surprisingly good condition.

Ian
Click to expand...

I don't understand why people would neglect brakes like this. Save money somewhere else. Driving is the single most dangerous thing most of us do on a regular basis. This makes it a whole lot more dangerous.
 
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