Rear Rotor Replacement?

Discussion in 'Parallel Universe' started by rideoregon, Jun 16, 2011.

  1. rideoregon

    rideoregon Adventurer

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    My 2009 F800 GS was in the shop today for a 12K mile checkup. I was told that my rear brake rotor was under minimum spec at 4.43 mm and should be replaced. The cost? $300 plus. I was none too thrilled to hear this and asked "how common is it for an F800 GS to need a new rear rotor at 12K miles?" The answer I got was vague. I decided not to have the work done. I want to gather more information and likely will replace the rotor myself possibly with an after market brand. Has anyone else had to replace their rotor this soon? I did a search and did not find discussion on this but surely this has come up. What are others experiencing with rear rotor wear/replacement? Any feedback is appreciated.
    #1
  2. Bayner

    Bayner Long timer

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    How many sets of pads have you gone through? If it's more than one, I would say it's at least plausible it needs replacing.
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  3. ebrabaek

    ebrabaek Long timer

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    That seems odd..... Unless you are dragging the rear brake off course. I just measured mine..... 7800 miles..... 4.98mm. You might want to measure it yourself for good measure.....:thumb:thumb

    Erling
    #3
  4. johngil

    johngil Reseda, CA

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    I'm at 4.6 - 4.7 on the brokeback beemer with just under 18,000 miles. I believe I'm on my fourth set of pads. Lots and lots of dirt and some mud.
    Pads were OEM, then Galfer black. Maybe a set of Galfer gold on now. I can't remember.
    #4
  5. JRWooden

    JRWooden Long timer

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    I'm still on the original set @ 17K miles, but they will be gone before much longer. I have a set of Galfer Greens ready to slap on, I bought the greens as the pkg said the greens were the easiest on the rotors.

    I've got 4.8 for thickness right now....
    #5
  6. rideoregon

    rideoregon Adventurer

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    I'm on my second pair of rear break pads having replaced the first set after 10.5K miles. I don't drag the brake. What I'm curious to know is what is typical mileage for replacing the rear rotor on the F8?
    #6
  7. ScienceOfDirt

    ScienceOfDirt U-Boat Rider

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    What is the minimum spec?
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  8. itsatdm

    itsatdm Long timer

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    New is 5mm. wear limit is 4.5mm
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  9. JRWooden

    JRWooden Long timer

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    Right ................. :lol3
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  10. rideoregon

    rideoregon Adventurer

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    The OEM rear rotor is $271.99 plus $1.59 ea. for the one time use bolts. Galfer sells a rotor for the F8, part # DF763W, MSRP-- $139.00. Much more like it! I'll be ordering the Galfer rotor from the local Cycle Gear along with a set of Galfer pads.
    #10
  11. rideoregon

    rideoregon Adventurer

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    Galfer misquoted the price. It's $186.00 not $139.00. Still better than $272.00 for the OEM.
    #11
  12. Hayate

    Hayate ADV Monkey

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    A friend of mine was surprised by the ridge on my rear rotor so mentioned I better get it measured. If my crappy old caliper is right and I'm reading it correctly I'm down to .133 inches, or 3.38mm. Way under spec eh? I just put my 5th set of rear pads on at 42,907 miles (2nd-4th, 7459, 18,200, 32,971 so about 10k each).

    So I'm wondering a couple things...

    First off a line of questions about rotor wear. So 4 sets of pads burnt 1.62mm of rear rotor and I was supposed to replace it after .50mm used? By my math that means a bit into the 2nd set of pads I'd be out of spec on the rotor? Like 15k miles and the rotor is done for? Is that normal? Can I do anything to prolong my next rotors life?

    The other set relate to the 4.5mm minimum spec. Why is that the minimum? Is it because the thinner the rotor gets the less it is able to absorb and dispense heat or is it because you need the width to get full pressure from the caliper? I don't sense a lack of rear brake power and mine is way past that point (I can easily get the ABS to engage using only rear brake on dry pavement and a rear Metzler Tourance for instance).

    I guess if I'm going to be replacing these things every 15k miles or anywhere in between that and my current 43k miles I'm not willing to pay what is it, $300? The Galfer option sounds better but what type of comparable wear factor will I get there? Are there other options?

    I love riding this thing, but I'm getting a bit overwhelmed this last riding season with the expenses involved in maintaining it... and I'm even doing it all in my garage now :(
    #12
  13. Hayate

    Hayate ADV Monkey

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    Are you sure that's the Galfer Roter for the 800gs? I just searched on it and found it on Amazon for $167 but plugging in BMW F800GS '09 it replied, this product does not fit. That and the pic shows only 4 bolt holes...

    Guess I'll search some more?

    ... More research confirmed that DF763W is our rear rotor... at least the catalog http://galferusa.com/catalog/ says "763" for the rear rotor. I guess the pic on amazon is just a stock photo of a Galfer wave rotor. I'm not sure why the match tool on Amazon says it isn't compatible. I'm pretty sure I'll order one.

    Best price seems to be Amazon for $167 with free shipping btw... I'll come back and update this if it works out.
    #13
  14. Hamish71

    Hamish71 Been here awhile

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  15. Reaver

    Reaver Outta Here

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    A 2009 with only 12k miles on it? That's also a problem! :rofl

    As I see it, there's three common ways to wear out a rear rotor. Normal use high mileage, lots of dirt/mud riding or you're a tail dragger. Riders who start out in the dirt tend to use the rear brakes a lot on the street. Now I'm not looking to start a "how to ride" thread nor am I saying I'm all that, but you really don't need your rear brake on the pavement. It has little effect anyway. My F8 has 45k kms on it with the original pads and rotor that's barely worn. It's been to Alaska and back so it's far from being a poser. The front brakes have two discs and four pads which are a lot more effective for stopping and wear better. Not saying your a bad rider but take note of how much you use the rear.

    To answer another question, the rotors have a minimum spec for a reason. If the rotor is thin AND the pads are really worn then you run the risk of blowing a puck and possibly locking the wheel. Rotors are often run past the limit but with thick pads. Under 4 mm is a bit excessive though, not worth the risk but YMMV.

    I've seen riders trade in their bike with shot rear brakes then bring their new bike (different model) shortly after and have the same complaint. Problem follows the rider.

    Just sayin'.
    #15
  16. JRWooden

    JRWooden Long timer

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    AND BOY ... that could ruin your entire day!

    IIRC, You being an aircraft mechanic - your comment has been permanently burned into a couple of the (few) remaining neurons I have left!

    Thanks, having never seen it, I had not thought of/considered that possibility.
    When I rebuild my calipers some distant number of miles from now, I'll be trying to figure out how the tolerances stack up and how badly this could go sideways.

    On a somewhat related note... I was in the auto parts store a while back and a guy brought in a "worn out" rotor from some car...
    It was worn down to the separation vanes on one side ..........there was no (continuous) metal bearing surface left..................
    I wanted to buy the rotor to hang on the wall in my garage, but the guy wasn't going for it ..............
    #16
  17. Reaver

    Reaver Outta Here

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    Oh, in that case I'm counting on you as backup! My liver is evil and I routinely administer the heavy handed punishment. My brain is just an innocent casualty of that war. :freaky


    Yes, I pretended to be an aircraft mech for 20 yrs but it sucked the joy out of flying. Then I pretended to be a BMW Motorrad Master Tech for a few years till it started to suck the joy out of riding. I still have flashbacks from both experiences. Doing what you love and the money will follow doesn't apply to me.

    Enough about me.....

    Of course the Dealer will suggest a new expensive rotor on the basis of "Safety" and quote the official spec you violated. If you don't "buy" into that, he may post an "I told you" on your work order to cover his ass. If you're on good terms and he likes you, the Dealer will advise you and tell you not to worry about it. The spec is for DOT reasons and must be met for a Certification or whatever you Mercans call it. Otherwise, real life has a different spec.

    I've seen my share of cheap ass owners. Like the guy with the K1200LT (light truck) that pulled in on a rainy day for a new rear tire. There was almost a foot long strip of cord showing! :eek1 He thought it was funny. Passed on a new front cause it still had a few miles left on it....... There are extremes to both sides of that coin.

    Your disc is fine. Ride safe!
    #17
  18. Reaver

    Reaver Outta Here

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    Well, if you're THAT bored.....

    I imagine that this anti-Darwinism safe world that North Americans live in now where idiots have just as much a right to life and the ability to sue that Engineers redesigned the caliper to make the grey area as thin as possible. Maybe it's an old wive's tale about what used to happen on Grandpa's ride back in the day. Maybe it's still an issue. I know it's easy to blow a puck when the disc thickness is ZERO :eek1. Oops, haven't we all done this at one time?

    Remember, cheap hurts......
    #18
  19. JRWooden

    JRWooden Long timer

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    My son helped me do the "zero" thing not too long ago,
    fortunately one stroke on the lever wasn't enough to do anything that would make the old man cuss :lol3
    #19
  20. Hayate

    Hayate ADV Monkey

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    Not get defensive, or add to making this a "how to ride" thread, but just to say the back brake does have plenty of stopping force for general "safe" stop light riding. I'm pretty sure it's been trained into me that the front brake being used anything more than gingerly is my lady friend pillion indication that it's an emergency situation. Maybe she's used to being on the back of bikes that don't dive like a submarine being spotted when the front brakes are laid on moderately? Anyway, I'm halfway through my first set of front pads while going through 4 sets of rear and more than having burned up the spec .5mm of rear rotor I guess I'm trying to justify that braking style.

    Anyway, back to my question, 1 1/2 pads go through the spec of the rotor, really? And what's "blowing a puck"? Is that where the piston would push all the way out of the caliper?
    #20