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Thread: Strange rear brake wear pattern

  1. #1
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    Strange rear brake wear pattern

    Has anyone seen this before?

    Rear brake pads are not contacting the entire width of the rotor. Previous owner's last brake pads were delivered with the car and they show the same pattern. All that occurs to me is that the pad is getting stuck on the top hangers and so the pressure is only in the middle? This pattern is visible on both the inside and outside of the rotor. Any insights greatly appreciated!

    1997 BMW 540i
    101,000 miles

    IMG_1780.jpgIMG_1779.jpg

  2. #2
    JimLev's Avatar
    JimLev is online now Artifically Aspirated Moderator
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    The ears on those pads look funky. When I use aftermarket pad I make sure the pads will slide back and forth in the caliper. I also use caliper grease on them.
    Also check the slide pins and the rubbers they go thru, they need to be clean. No brake dust buildup.

  3. #3
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    Quote Originally Posted by JimLev View Post
    The ears on those pads look funky. When I use aftermarket pad I make sure the pads will slide back and forth in the caliper. I also use caliper grease on them.
    Also check the slide pins and the rubbers they go thru, they need to be clean. No brake dust buildup.
    Boy, howdy. They sure do.
    Is that is the chicken or the egg? I wonder if something damaged is causing the pads to bind and the action of the caliper is grinding at the ears.
    With caliper installed and no pads and the piston fully retracted the caliper should be able to slide in/out fairly easily by hand. I'd then check with one pad at at a time to see if binding.
    Lots of brake jobs go south in a hurry because of no or sloppy preparation.
    those rotors are probably junk.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  4. #4
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    As posted before, Those pads are not hitting the rotor square.

    Causes of funking wear pattern on pads: Caliper binding on floating pins or within the bracket itself, Caliper brackets having wear pattern where the pad "ears" sit, (file flat, clean all material - pad material will harden to a steel like hump all over the caliper brackets)

    Bottom line: Someone hung pads on this car with out any prep work, now you have become the next owner of the car. Congrats!

    Solution: Remove caliper brackets, clean, file down the areas where the pad ears sit, re-install with new pads, rotor, use hi-temp caliper grease on the contact points. Bleed the braking system AFTER checking the rubber hoses for deterioration, and confirming the calipers are not hanging up and retract after line pressure is at ZERO.

    Recommendations:
    Replace all the rubber brake hoses (six of them - two are in the engine bay). Read the DIY on complete brake overhauls as caliper seals only last a 100K if no one has done it before there will be water in behind the pistons eating away piston material requiring new pistons (cheap and easy rebuild process).

    Easy fix good luck! This pad wear problem has been around since disc brakes became common on cars...like in the the 1970's. You issue is not rare and the solutions have not changed one bit.

    Helpful?
    Attached Images Attached Images
    Last edited by StephenVA; 03-27-2020 at 09:41 AM.
    Current Garage Highlights
    2005 X5 4.8is Le Mans Met Blue
    2003 525iT TiSilver
    2002 M5 TiSilver
    1998 528i KASCHMIRBEIGE METALLIC (301) (Goldie)

    Former Garage Highlights
    2004 325iTs (2x)
    1973 Pantera L
    1971 Dodge Dart Swinger "Lite Package"
    1970 Dodge Challenger T/A 340 Six Pack Alpine White
    1970 Dodge Challenger T/A 340 Six Pack GoManGo Green
    1969 Road Runner 383
    1968 Barracuda Formula S 340 Sea Foam Green

  5. #5
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    Very helpful! I just followed the process you suggested and reinstalled the old pads and rotors to test whether this would fix the problem. It did! Thanks! Of course, the next step is to order new replacements.

  6. #6
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    Congrats! Next issue...
    Current Garage Highlights
    2005 X5 4.8is Le Mans Met Blue
    2003 525iT TiSilver
    2002 M5 TiSilver
    1998 528i KASCHMIRBEIGE METALLIC (301) (Goldie)

    Former Garage Highlights
    2004 325iTs (2x)
    1973 Pantera L
    1971 Dodge Dart Swinger "Lite Package"
    1970 Dodge Challenger T/A 340 Six Pack Alpine White
    1970 Dodge Challenger T/A 340 Six Pack GoManGo Green
    1969 Road Runner 383
    1968 Barracuda Formula S 340 Sea Foam Green

  7. #7
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    Late to the party here. Those pads looks like they've been in a salt bath. Minnesota, eh? That's probably part of your answer. Just replace, as a minimum, pads and rotors as soon as you can. Check everything else (pins, bushings etc.) and replace if suspect. Lube all the caliper bracket where the pad ears slide. They're not supposed to touch but everything has some flex so best to lube.

  8. #8
    Jaaap's Avatar
    Jaaap is offline ☀ ☁ ☂ ☃ ☏ ☠ ☢ ☣ ♕ ♫ ✂
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    Am i crazy or do these pads and rotors look pretty normal (for worn items)?
    I expect nothing less when i buy a second hand BMW.

  9. #9
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    The issue is the band of rust at the top and bottom of the rotor/pad. Effectively renders the rear brakes to 60-70% capacity and shifting brake bias forward. I should note that this was a one-owner car for its entire life up until two weeks ago. The previous owner was a great friend who took great care of his cars. The car sat for about two years while his health deteriorated and I bought it from his widow. I say all this because I know this car was loved and cared for by a competent owner. It's just clear that checking the condition of the carrier and pad ears for corrosion should be a routine service item for DIYers.

    Jim

  10. #10
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    Jim, sorry about your friend. Since the car sat for those couple of years, rubber really takes a toll. Pull the calipers off, open them up, inspect the pistons and check for rust and pitting, if bad, order new ones from FCPeuro, they're cheap, don't screw around, get what came in them, ATE. Thats who made the calipers, oreder those, and definitely order a caliper rebuild kit, they're like ten bucks per caliper. If the old brake fluid was bad, there will be rust in there, make sure you bleed out the whole brake system, this will include operating the solenoid sin the ABS module, so be prepared to do this job properly. Definitely open up the front calipers too. And since you will be opening up the cubbyhole where the brake booster sits, underneath the drivers side cabin filter housing, clean out that whole compartment as there is a drain hole down there that can get clogged up with debris, if water pools up in there, it gets sucked into the booster.
    Set the controls for the heart of the sun

  11. #11
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    Thanks BimmrMeUpSnotty. I've been doing a lot of fluid changes and general maintenance to catch the car up. I ordered everything for the full brake restoration even though I flushed the brake fluid a week ago (oops - order of operations matters huh!). I appreciate your thoughts on my friend. It's been wonderful having the car to stay connected with him. In fact, a few years ago, I did a full suspension refresh and alignment with him. Working on and under the car brings back great memories. Especially nice given the pandemic lockdown. Gives me something fun to do.

    Thanks to everyone for your comments!

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