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Hey folks, have odd issue with rear brakes after installing new pads.

The story:

Back in October 2016 iDrive started warning about rear brake pads. Got extra message about minimum thickness after couple more days of driving (~30 more miles on odometer later). Got pads and then...subsequent brutal winter stopped all things M5 in my life for several months.

Fast-forward to late February 2017. Changed rear pads, found this video useful in regards to tearing down HVAC and the mm sizes needed for the tools: https://www.youtube.com/watch?v=ySF5n2QBAZ0

I post that video because that guy's experience in it matched my experience changing the pads; easy brake pad replacement, no drama. I did not change the sensor. Pads were these: http://www.autozone.com/brakes-and-traction-control/brake-pads/duralast-gold-brake-pads/823331_421373_1610

Despite being careful with the calipers, I still found mushy pedal response after putting car back together. Being lazy, I just took it to Meineke (was this a mistake?) and got a full flush. Was careful to make sure they used the DOT4 full synthetic (they had to grab some from other location) and left HVAC dissambled to mitigate any possible antics by Mieneke tech accessing the master.

The problem:

Drove car since Meineke for a couple hundred miles after setting the pads. I noticed some rotor dust persisting and assumed it was just taking time to clear up.

The rust though has not cleared up, and is now clearly dilineated. Identical inner rust rings on both rear rotors. Car stops fine, pedal feels fine, no shimmies etc., grip does not feel 100% (which is what got me really paying attention to this). I'd say contact is about 80% all together what it should be on the rears.

See attached photo for details; the piece of paper is pricetag off some socks jammed far as I can force it, just to illustrate clearance on the inner part of pads seems tight enough that surface should grab with rest the pad. Rotors in photo are room temp, going to manually clean the rust off to keep pitting from happening (though it looks in progress from the photo...ugggh).

I included the Meineke details just for full accounting of the brake maintenance; but this seems a mistake by me installing the pads given Meineke tech never needed to pull calipers. I've read around the board for anything resembling this issue, and found some details here: http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/403314-incomplete-pad-contact-front-rotors.html

But that problem is front brakes and inverse (outer rotor) to my problem with inner-rotor surface. I did not grease the guide bolts, I did clean up the calipers when I had them out - and the problem is identical for both rear rotors, so I did something wrong I think - but if I took them apart again now I wouldn't know what to fix from original process.

Any thoughts on this from resident M5 ninjas?
 

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Drove car since Meineke for a couple hundred miles after setting the pads. I noticed some rotor dust persisting and assumed it was just taking time to clear up.
I think you need to properly 'bed' in the pads into the rotor. Just driving normally wont do it.

Do a few hard stops from ~100 to about 30 about 3 times right after another, then let the brakes cool off by just cruising not using them.
 

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Discussion Starter #3
I think you need to properly 'bed' in the pads into the rotor. Just driving normally wont do it.

Do a few hard stops from ~100 to about 30 about 3 times right after another, then let the brakes cool off by just cruising not using them.
Thanks for the tip. I cleaned 99% of the rust off and will see if the hard-bedding you recommend takes care of that last 1%.

And advice that essentially consists of "go fast to fix it" is quintessential M - so it must work :grin

Also checked out your car and what a nice one (nice plates too). IB was only thing I wanted that I didn't get upon finding my proverbial unicorn.
 

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And advice that essentially consists of "go fast to fix it" is quintessential M - so it must work :grin

Also checked out your car and what a nice one (nice plates too). IB was only thing I wanted that I didn't get upon finding my proverbial unicorn.
Haha now thats funny!!

Thanks! I got very lucky with the car I ended up with. Any pics of your unicorn?
 

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Discussion Starter #5 (Edited)
Haha now thats funny!!

Thanks! I got very lucky with the car I ended up with. Any pics of your unicorn?

I was very lucky with my car as well; one-owner perfectly OEM stock. It has every option except the folding rear seat, and all those options work and have continued to do so. I should glue a horn on the hood because it seems an actual unicorn that way.

With the weather agreeable again, and out driving the car again, I find myself coming to this board and scrolling through the custom wheels thread and wondering about exhaust and looking up wrap colors and so forth.

P.S. I rolled a country highway today - racetrack, I meant racetrack officer lol - trying your brake-set advice. I wish I had not cleaned the rotors now because they're shiny as when I cleaned them...doh. A tiny rusty film remains, but I'll have to drive it another day or two to see if it goes away completely. Grip/stopping feels natural to the car. Only more miles will tell, and that will be the easy part!
 

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With the weather agreeable again, and out driving the car again, I find myself coming to this board and scrolling through the custom wheels thread and wondering about exhaust and looking up wrap colors and so forth.
Very nice man!

The forum will do that to you ha. Stock cars are boring for me so I have always been a modifier. Have fun with it!
 

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Why did you not change the sensor?

I'd wonder about the sub par quality pad from Autozone...

I installed new OEM pads and they work with no bedding (even contact first application). $120 from the dealer. Sensor only cost me $23.

Many times you get what you pay for...brakes are pretty important on a 4000 pound car able to do 204 mph.
 

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Possible causes:
Wrong Pads/ Pads not sitted correctly
One of Pistons in the Caliper stuck due to rust or piston pushed in too far back during installation of new pads
Master cylinder not providing enough pressure

It will be worth it to remove and check pads and caliper

This is along shot but check thickness of rear disc, should be 24mm Max and 22.4mm minimum. It is good practice to use copper slip on non friction/contact surfaces.

Check the sensor position, if it has not been replaced with new, it might not fit properly as it would have already worn down
 
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