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60 posts

Master Geek


  # 2283862 26-Jul-2019 09:21
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Oil wheel nut threads seats and take care tightening them especially on magnesium wheels with no taper.  Bake rotor uneven wear starts somewhere and I would not discount this as a possibility after some of the tough nuts I have come across.   


679 posts

Ultimate Geek


  # 2284260 26-Jul-2019 14:53
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1eStar: I had a car with bad brake shimmy which was exacerbated by heat from braking. I replaced the discs and it fixed the problem. However after the next 180km/h to 100km/h deceleration session the problem came back.

 

Going to ask the dumb question, but was this the first decent brake application or had they been fully bedded in prior to the race level deceleration?

 

 





 
 
 
 


5573 posts

Uber Geek


  # 2284266 26-Jul-2019 15:01
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Batman:

 

1eStar: I had a car with bad brake shimmy which was exacerbated by heat from braking. I replaced the discs and it fixed the problem. However after the next 180km/h to 100km/h deceleration session the problem came back.

 

i think i'm going to diagnose warped discs from overheating!

 

 

More likely to be DTV due to unevenly deposited pad material on the rotor surface. It's exceptionally hard to actually warp a brake rotor - it is almost always uneven material buildup from using a pad compound that isn't suited to the driving style, or clamping a hot stationary rotor between a hot pad and bits of the pad surface adhering to the rotor and tearing away.


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Uber Geek


  # 2284269 26-Jul-2019 15:05
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GGJohnstone:

 

Oil wheel nut threads seats and take care tightening them especially on magnesium wheels with no taper. 

 

 

I'd suggest that oiling (or any other lubricant) on a thread is a very bad idea. It means the toque required to do up the fastener is greatly reduced and increases the likelihood of over tightening that leads to failure of the stud or bolt. Threads should be clean of any contamination, but unless the manufacturer specifies a certain lubricant be put on the threads, don't do it.


679 posts

Ultimate Geek


  # 2284270 26-Jul-2019 15:06
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RunningMan:

 

Batman:

 

1eStar: I had a car with bad brake shimmy which was exacerbated by heat from braking. I replaced the discs and it fixed the problem. However after the next 180km/h to 100km/h deceleration session the problem came back.

 

i think i'm going to diagnose warped discs from overheating!

 

 

More likely to be DTV due to unevenly deposited pad material on the rotor surface. It's exceptionally hard to actually warp a brake rotor - it is almost always uneven material buildup from using a pad compound that isn't suited to the driving style, or clamping a hot stationary rotor between a hot pad and bits of the pad surface adhering to the rotor and tearing away.

 

 

Haven't found it that hard to warp them.  Usually a cheaper rotor that isn't really up to the performance level of it's use.  Or one that is near the minimum thickness and not as easily able to dissipate the heat build up.  Or failure to properly bed them in before hard use.

 

But yes, there are many ways to achieve brake shuddering.





5573 posts

Uber Geek


  # 2284274 26-Jul-2019 15:14
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Bit different on a motorsport car though, especially with standard brake components. Normal road car very unlikely to get into that sort of range.


679 posts

Ultimate Geek


  # 2284276 26-Jul-2019 15:21
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RunningMan:

 

Bit different on a motorsport car though, especially with standard brake components. Normal road car very unlikely to get into that sort of range.

 

 

Fully agree.  The only thing standard about the rally car brakes is that they are the same size as stock.  Pads, rotors and fluid all uprated from stock.

 

Just have to take care when then driving the stock standard daily Corolla over the Remutaka hill slightly more enthusiastically than its very standard brakes could handle.  To be fair though, the pads overheated and stopped biting before the rotors warped.  It now has better pads.  :-)

 

 





 
 
 
 




Mad Scientist
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Uber Geek

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  # 2284312 26-Jul-2019 16:34
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RunningMan:

 

Batman:

 

1eStar: I had a car with bad brake shimmy which was exacerbated by heat from braking. I replaced the discs and it fixed the problem. However after the next 180km/h to 100km/h deceleration session the problem came back.

 

i think i'm going to diagnose warped discs from overheating!

 

 

More likely to be DTV due to unevenly deposited pad material on the rotor surface. It's exceptionally hard to actually warp a brake rotor - it is almost always uneven material buildup from using a pad compound that isn't suited to the driving style, or clamping a hot stationary rotor between a hot pad and bits of the pad surface adhering to the rotor and tearing away.

 

 

that's what the internet says.

 

but i had an SUV that's done 10,000ks. perfectly fine brakes.

 

then i charged down a mountain and braked heavily at every corner, and towards the bottom of the mount, the steering developed judder. 

 

from nothing to bad judder.

 

if that's not warped discs I don't know what.

 

no, i did not stop halfway and apply brakes.

 

funny thing was - took it back to dealer and he said you shouldn't use the brakes to slow down.





Involuntary autocorrect in operation on mobile device. Apologies in advance.


60 posts

Master Geek


  # 2284336 26-Jul-2019 17:16
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Further to my comment regarding lubricating wheel nuts:  An outspoken engineer, entertainer that I have seen on you tube has firm opinions regarding this matter.  It is possible from what he has said that if you randomly tighten nuts without regard to a proper star pattern sequence you could damage a brake disk.  I suggest that similar result may occur if the nuts were not clean and lubricated to ensure proper loading to the studs and the disk if it is mounted in such a manner.  The force applied to the wrench is greatly amplified by the threads and friction losses to nut rotation might be amplified similarly and permanent damage result.

 

Certainly worth a look at the engineers rant.


5573 posts

Uber Geek


  # 2284352 26-Jul-2019 18:19
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1528 posts

Uber Geek


  # 2284640 27-Jul-2019 17:44
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geoffwnz:

1eStar: I had a car with bad brake shimmy which was exacerbated by heat from braking. I replaced the discs and it fixed the problem. However after the next 180km/h to 100km/h deceleration session the problem came back.


Going to ask the dumb question, but was this the first decent brake application or had they been fully bedded in prior to the race level deceleration?


 



Well bedded in. Used the car normally for several years with smooth brakes. The brakes were somewhat undersized so I ran the best pads I could find. I also subscribe to the idea that the wheelnuts need to be torqued evenly, I had been fastidious in this regard, however just prior to this high speed slowdown I had had a tyre shop refit the wheel and it was not torqued using a wrench. So I'm blaming both the heat from the undersized rotors and the uncertain torque levels for the warping of the rotors.

1528 posts

Uber Geek


  # 2284641 27-Jul-2019 17:44
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geoffwnz:

1eStar: I had a car with bad brake shimmy which was exacerbated by heat from braking. I replaced the discs and it fixed the problem. However after the next 180km/h to 100km/h deceleration session the problem came back.


Going to ask the dumb question, but was this the first decent brake application or had they been fully bedded in prior to the race level deceleration?


 



Well bedded in. Used the car normally for several years with smooth brakes. The brakes were somewhat undersized so I ran the best pads I could find. I also subscribe to the idea that the wheelnuts need to be torqued evenly, I had been fastidious in this regard, however just prior to this high speed slowdown I had had a tyre shop refit the wheel and it was not torqued using a wrench. So I'm blaming both the heat from the undersized rotors and the uncertain torque levels for the warping of the rotors.

679 posts

Ultimate Geek


  # 2285047 29-Jul-2019 09:21
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1eStar:
geoffwnz:

 

1eStar: I had a car with bad brake shimmy which was exacerbated by heat from braking. I replaced the discs and it fixed the problem. However after the next 180km/h to 100km/h deceleration session the problem came back.

 

Going to ask the dumb question, but was this the first decent brake application or had they been fully bedded in prior to the race level deceleration?

 



Well bedded in. Used the car normally for several years with smooth brakes. The brakes were somewhat undersized so I ran the best pads I could find. I also subscribe to the idea that the wheelnuts need to be torqued evenly, I had been fastidious in this regard, however just prior to this high speed slowdown I had had a tyre shop refit the wheel and it was not torqued using a wrench. So I'm blaming both the heat from the undersized rotors and the uncertain torque levels for the warping of the rotors.

 

cool.  Reading the initial post could be interpreted that you replaced them, then went straight out and baked them.  But yep, I'd be suspicious of the wheel nut torque in general.  Had a fair few tyre shops who just set the impact wrench on maximum and then apply 10-12 ugga-duggas after the nut stops rotating.





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