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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 05-11-2014, 05:16 PM
Burnsy Burnsy is offline
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Rotors will not come off :'(

I have tried just about everything between sledge hammer all the way to heating and nothing will get this back rotor to come off. The front one slid off perfectly with one hit.

Any tips?
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  #2  
Old 05-11-2014, 05:50 PM
PWH42 PWH42 is offline
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You could drill a hold large enough to screw in a hardened threaded bold with a ratchet. As you screw the bolt into the rotor, the pressure of the bolt will snap the rotor in half an it will be off. This of course assuming you are replacing the rotor. I have used this method a few times and it works well.

Last edited by PWH42; 05-11-2014 at 05:51 PM.
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Old 05-11-2014, 06:02 PM
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Originally Posted by PWH42 View Post
You could drill a hold large enough to screw in a hardened threaded bold with a ratchet. As you screw the bolt into the rotor, the pressure of the bolt will snap the rotor in half an it will be off. This of course assuming you are replacing the rotor. I have used this method a few times and it works well.
Not sure I have a drill bit large enough to size up with any of the bolts I have. I'm assuming I drill in the center, correct?
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Old 05-11-2014, 06:59 PM
PWH42 PWH42 is offline
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Doesn't have to be very big bit - Drill on the face of the rotor... Need to use a hardened drill bit or it will snap.
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Old 05-11-2014, 07:31 PM
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Originally Posted by Burnsy View Post
Any tips?
Penetrating oil, patience and a sledgehammer. Earplugs are helpful, too. Heat can be tough if you're working with only a propane utility torch because the rotor & hub make such an effective heat sink.

When I've had to resort to the sledge, I've found it helps to rotate the disc a quarter-turn between strikes. Also, the occasional hit in the wrong direction (i.e., on the outer face) can work wonders.
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Old 05-11-2014, 09:19 PM
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Originally Posted by Burnsy View Post
I have tried just about everything between sledge hammer all the way to heating and nothing will get this back rotor to come off. The front one slid off perfectly with one hit.
Make sure that the parking brake is OFF, and you might also have to adjust the parking brake shoe to retract it from the integral drum. Occasionally they get a little tight/worn.
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  #7  
Old 05-12-2014, 01:28 AM
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DSXMachina DSXMachina is offline
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Originally Posted by Burnsy View Post
I have tried just about everything between sledge hammer all the way to heating and nothing will get this back rotor to come off. The front one slid off perfectly with one hit.

Any tips?
Penetrating oil. And then an air hammer all around the hat until it pops. You don't have an air hammer? Try Zeichen's method posted above as it is the approved and best method. Still can't get them?
Then you need a bigger sledge, or as we say at the shop, a BFS. A real sledge hammer will have a 3' handle and a 10 lb. head. And you swing it like Thor. I have a feeling you did not use a BFS or those rotors would be on the ground. We win every time. Who cares about the rotors, time is money, and you're not putting the old ones back on, right?

Last edited by DSXMachina; 05-12-2014 at 01:30 AM.
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Old 05-12-2014, 01:32 AM
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DSXMachina DSXMachina is offline
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Originally Posted by PWH42 View Post
Doesn't have to be very big bit - Drill on the face of the rotor... Need to use a hardened drill bit or it will snap.
That's 'cuz the rotors are cast iron, not steel. Much less flexible, but much harder.
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  #9  
Old 05-12-2014, 03:00 AM
hondo402000 hondo402000 is offline
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cast iron is softer than steel, why do you think they wear out
are you sure the parking brake is off
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Old 05-12-2014, 04:48 AM
sunny5280 sunny5280 is online now
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I'd substitute a dead-blow mallet instead of the BFS.
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  #11  
Old 05-12-2014, 05:59 AM
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cast iron is softer than steel, why do you think they wear out
are you sure the parking brake is off
Would steel rotors be a cheap alternative to ceramic brakes then? I always thought discs wore out from the abrasive nature of braking rather than the fact they were cast iron.
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Old 05-12-2014, 06:06 AM
luigi524td luigi524td is online now
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Exclamation removing brake disc

Quote:
Originally Posted by Burnsy View Post
I have tried just about everything between sledge hammer all the way to heating and nothing will get this back rotor to come off. The front one slid off perfectly with one hit.
Any tips?
Are you sure you removed the 8mm hex bolt that holds it on? I remember my first BMW brake job ... all my previous cars had the brake disc held on by sheer luck and the wheels ... only BMW would think to add a bolt that sometimes is flush with the disc and hidden and disguised by rust and road stuff!
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  #13  
Old 05-12-2014, 06:20 AM
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DSXMachina DSXMachina is offline
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Originally Posted by hondo402000 View Post
cast iron is softer than steel, why do you think they wear out
are you sure the parking brake is off
I said that rotors being cast iron were harder than steel. I should have known better than to make a blanket statement. The fact is now that I think about it I'm not sure. It all depends on whether it has been hardened or not, and what the tempering process has produced. Hardened cast iron (Martensitic) can be much harder than most commonly encountered steels.

But I don't know what process rotors have been through. And steel can be low alloy steel, carbon steel or stainless steel followed by any number of treatments which can harden them. Some cast iron can easily hit Rockwell C 50, and some steels are softer at the upper 20's or the low 30's. OTOH steel can easily get into the really hard Rockwell C 55 range, and cast iron can be in the 20's. I'll see if I can find out where cast iron rotors fall.
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Old 05-12-2014, 06:49 AM
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Zeichen311 Zeichen311 is offline
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Originally Posted by DSXMachina View Post
I'll see if I can find out where cast iron rotors fall.
Right on your toes, after the ultimate swing of the BFS. (I've been chuckling all morning at the mental image of the Mighty DSXThor attacking unworthy rotors with Mjolnir...and wondering whether the horns on the helmet ever get hung up on the undercarriage. And what's best for cleaning grease from a cape?)

Very curious to hear what you dig up about the properties of rotors (and I sense an impending side discussion on the distinction between hardness and toughness...).
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  #15  
Old 05-12-2014, 07:24 AM
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Originally Posted by floydarogers View Post
Make sure that the parking brake is OFF, and you might also have to adjust the parking brake shoe to retract it from the integral drum. Occasionally they get a little tight/worn.

Outch!
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  #16  
Old 05-12-2014, 07:30 AM
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DSXMachina DSXMachina is offline
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[snip]
I sense an impending side discussion on the distinction between hardness and toughness...
Hardness is fairly objective, but toughness has malleability, compressive strength, tensile strength, corrosion resistance, etc. as variables. For arguments sake I'll let it go as "toughness". In that case our discussion has to include hardness, toughness and...machinability because none of those terms mean anything to the other two. I will begin the lesson with a discussion of Austenite, Martensite and Pearlite, then Stalagmites and Stalactites. A short quiz will follow to see who has been paying attention.

Last edited by DSXMachina; 05-12-2014 at 08:35 AM. Reason: Stalagtites corrected to stalactites per Zooks.
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Old 05-12-2014, 07:31 AM
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Quote:
Originally Posted by DSXMachina View Post
I said that rotors being cast iron were harder than steel. I should have known better than to make a blanket statement. The fact is now that I think about it I'm not sure. It all depends on whether it has been hardened or not, and what the tempering process has produced. Hardened cast iron (Martensitic) can be much harder than most commonly encountered steels.

But I don't know what process rotors have been through. And steel can be low alloy steel, carbon steel or stainless steel followed by any number of treatments which can harden them. Some cast iron can easily hit Rockwell C 50, and some steels are softer at the upper 20's or the low 30's. OTOH steel can easily get into the really hard Rockwell C 55 range, and cast iron can be in the 20's. I'll see if I can find out where cast iron rotors fall.

Bu Gum, DSX, you're on to something!

Any sword smith knows that to achieve a hard edge that keeps its sharp, you gotta heat at least red hot, then cool suddenly. Left to cool slowly, softer but far more flexible steel is obtained. Thus, smiths of old heated the blade, then dripped water on the edge.

But those smiths also knew that hard edge is terribly brittle! So here's what I recommend:
  • Obtain furnace nozzle from hot process such as molten glass reservoirs
  • Provide adequate ventilation
  • Train flame on wheel
  • When glowing red, remove flame
  • Douse glowing red wheel with fire hose
  • When fog clears, tap rotor with peen hammer - comes right off!!!
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Old 05-12-2014, 07:43 AM
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Originally Posted by CALWATERBOY View Post
Bu Gum, DSX, you're on to something!

Any sword smith knows that to achieve a hard edge that keeps its sharp, you gotta heat at least red hot, then cool suddenly. Left to cool slowly, softer but far more flexible steel is obtained. Thus, smiths of old heated the blade, then dripped water on the edge.


But those smiths also knew that hard edge is terribly brittle! So here's what I recommend:
  • Obtain furnace nozzle from hot process such as molten glass reservoirs
  • Provide adequate ventilation
  • Train flame on wheel
  • When glowing red, remove flame
  • Douse glowing red wheel with fire hose
  • When fog clears, tap rotor with peen hammer - comes right off!!!
A great video having to do with Japanese sword making. It's heavy on the science of metallurgy, but also leaves a lasting respect for the art. My very best kitchen knives pale in comparison.
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Old 05-12-2014, 08:01 AM
ptrcd003 ptrcd003 is online now
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Originally Posted by luigi524td View Post
only BMW would think to add a bolt that sometimes is flush with the disc and hidden and disguised by rust and road stuff!
At least they had the foresight to make it a hex bolt. Ever tried to do the same job, but with a philips screw? I was helping a buddy do his brakes on an Accord, and spent many hours cursing Honda as I extracted the screws.
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Old 05-12-2014, 08:02 AM
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Originally Posted by DSXMachina View Post
I will begin the lesson with a discussion of Austenite, Martensite and Pearlite, then Stalagmites and Stalagtites. A short quiz will follow to see who has been paying attention.
Stalactite.

Another hero defenestrated.


Quote:
Originally Posted by DSXMachina View Post
A great video having to do with Japanese sword making. It's heavy on the science of metallurgy, but also leaves a lasting respect for the art. My very best kitchen knives pale in comparison.
Folded steel is so pretty, as is Damascus. Wonderful look in a shotgun barrel, with a strongly debated / disputed reputation for coming apart badly.
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Old 05-12-2014, 08:13 AM
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Originally Posted by DSXMachina View Post
A great video having to do with Japanese sword making. It's heavy on the science of metallurgy, but also leaves a lasting respect for the art. My very best kitchen knives pale in comparison.

That's how I make my kitchen knives!

My Hamons are sinusoidal.
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Old 05-12-2014, 08:15 AM
fdriller9 fdriller9 is online now
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I had this happen to me once. I forget to release the parking brake.

I was wailing on the thing with a hammer for about 30 minutes before I realized my stupidity haha

Normally if you hit the rotor on the edge of the hat, it will come right off.
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Old 05-12-2014, 08:34 AM
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Originally Posted by Zooks527 View Post
Stalactite.

Another hero defenestrated.




Folded steel is so pretty, as is Damascus. Wonderful look in a shotgun barrel, with a strongly debated / disputed reputation for coming apart badly.
When you mean tossed out the window, just say tossed out the window. No need to go all French on us. Would you believe my spell-check flagged stalagtite and I overruled it?

Here in the buckle on the rust belt we learned that rotors will seize onto the hub given the slightest opportunity. Reassembly always involves some anti-seize applied to the hub, especially in the center which fits into the rotor.
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Old 05-12-2014, 08:40 AM
hondo402000 hondo402000 is offline
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typically Cast Iron Rotors are not Chill hardened or go thru any hardening process, why do you think the rotors thin out, because the cast iron is soft and gets worn away,
and the other reason they are not hardened is because of the braking process, once they get hot and cool down slowly it would make them soft again

Usually they are cast, cooled slowly and then machined and balanced and thats it
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Old 05-12-2014, 09:11 AM
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DSXMachina DSXMachina is offline
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Originally Posted by hondo402000 View Post
typically Cast Iron Rotors are not Chill hardened or go thru any hardening process, why do you think the rotors thin out, because the cast iron is soft and gets worn away,
and the other reason they are not hardened is because of the braking process, once they get hot and cool down slowly it would make them soft again

Usually they are cast, cooled slowly and then machined and balanced and thats it
I've done my homework and you are correct. There are basically four different alloys of grey iron used for automotive parts, two of them for rotors. Rockwell C hardness ranges from 15 to 20. That is relatively soft in comparison to most steels.
That said, there is more to machinability than hardness and my first post in reference to the difficulty of drilling cast iron as compared to steel stands. Cast iron is softer than steel but it's harder to drill.
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