Rear Rotor Replacement?

[JRWooden]

Originally Posted by Reaver

... 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....

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 ..............

[Reaver]

Originally Posted by JRWooden

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

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.


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! 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!

[Reaver]

Originally Posted by JRWooden

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.

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 . Oops, haven't we all done this at one time?

Remember, cheap hurts......

[JRWooden]

Originally Posted by Reaver

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 . Oops, haven't we all done this at one time?

Remember, cheap hurts......

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

[Hayate]

Originally Posted by Reaver

. 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...

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'.

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?

[JRWooden]

Originally Posted by Reaver

... 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.

I've tried the same approach and have found that:
1) I fall out of love more often than the average career-man
2) The money may follow, but it's so damn far behind I can't see it ever catching up to me

[JRWooden]

Originally Posted by Hayate

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?

Learning to ride off-road I use more back brake than some folks - I think on my bike I'll end up replacing the rear about twice as often as the front (I have the F650GS-twin, so only one front caliper).

I agree the submarine aspect of the F650GS is disconcerting and would be worse with passenger!
(I've never ridden an F800GS so can say there)

Although some folks don't think so highly of them, I installed the Ricor Intiminators
http://www.advrider.com/forums/showthread.php?t=489675
and they fixed the U-boat issue I think it was a great modification for the price (if you buy: wait for a sale).

Yes, blowing a puck would be having a caliper piston leave the bore in the caliper far enough to get cocked and create a huge issue.

[Reaver]

Conversations here can quickly go south due to one mistype or just from the reader being in a bad mood so I tend to tip toe when suggesting a cause might not be the bikes fault. Since I haven't met these people or seen their bikes, one can only specualte. Or ass-u-me.

The other factor regarding accelerated brake wear is weight. Another touchy subject. A fully bagged out bike or riding two up will definately increase brake wear. I once had the pleasure of trying to explain to a customer why his 658 was sluggish and went through rear brakes so often. He used it like a scooter doing errands in town and never took it on the highway cause it was slow and unsteady. Ummm, the poor bike was severely overloaded just by him sitting on it. Ever seen a lowered 658 overloaded? Ever seen a Russion Bear on a bicycle? I could hear metal groaning noises in my head. The centre of gravity rolled about on every bump or lean. I suggested using the maximum tire pressure. He said that was "two up" pressure and he never carried a passenger. Oh boy.

All I can say for certain is that it's not a bike specific problem or design error. Maybe a bad batch of rotors..... My F8 and the gf's 658 have been all over and still run the original brakes. Little mud use, reasonably loaded and I suppose I use a lot of engine braking as well.

As my French buddy always says "sorry bout yer luck!"

[High Country Herb]

Originally Posted by rideoregon

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.

It isn't uncommon that performance aftermarket cost less than OEM, no matter what type of vehicle. Wise choice looking into that. No garantee it will last longer than OEM, but it may have more stopping power. Someone mentioned the green Galfer pads, and that may be a way top extend the life of the rotor.

I've never actually seen a puck come out of the caliper, but I've seen them become shifty when extended too far. That leads to dragging brakes, because the puck won't retract all the way once damaged. (Subaru) Thin rotors don't dissapate heat as well either, which leads to warped rotors. It's all a vicious circle...

That reminds me...my old XL has about 1.5mm of pad left, I better change them.

[gus007]

I am confused by the whole rotor wearing thing. I have replaced rotors on a car but that car had about 150,000 miles on it and I ran it pretty hard, but I have never replaced rotors on a motorcycle due to wear. I've upgraded to stainless steel on my racebike but that was for performance reasons. And I replaced a couple of rotors due to crashes but I would think the rear rotor should pretty much last forever unless you are very large and/or drag the rear break and/or have a very large passenger riding full time. That's my opinion.

Because of this thread I went and checked the rear rotor on my bike and it is noticeably grooved and I never use the rear on the pavement but I do on gravel and off-road. I've noticed the rear brake on my bike also has a tendency to lockup . Could this be due to a worn rear rotor? Could this be another one of BMW's ways to reduce costs with substandard components? It's not that expensive to replace with an aftermarket fix so I feel pretty lucky with only having to spend around ~$180 to take care of it.

[Hayate]

Originally Posted by gus007

rear rotor should pretty much last forever unless you are very large and/or drag the rear break and/or have a very large passenger riding full time. That's my opinion.

.

My girlfriend is pretty sure you're calling her fat!

Galfer did get back to me to double confirm what I found in their catalog btw. Pretty damn sure now the rear rotor available on Amazon is the one for the F800gs (same for f650gs).

Justin at Galfer wrote:
Regarding your BMW F 800GS,
The DF763W rotor is the correct rotor for your bike.

[Hayate]

I've found some other options now too. A company called "Braking" which I know nothing about, but their catalog does show that this rear rotor is right for the F800GS and it's only $110 on Amazon. Anyone want to chime in on them?
http://www.amazon.com/Braking-Wave-B...1&s=automotive

[Gaspare]

You can trust them: they produce quality products - made in Italy.
Not that sure, but they invented the wave disc; at least they are pioneers in it and their R&D is a world leader (SUNSTAR Group since 2004).

Last "new" (racing since 2002) is batfly rotor; quite expensive but seems to be effective more than it's cool.
They anyway produce different options for F800 GS rotors: let's have a look @ http://www.braking.com/ catalog and choose the pony...