Our rotors dont warp.

[svxsubaru1]

I have read this before and have been wanting to post this because it has worked for me on a couple of cars for me when the disc start to "warp" i put on some hard semi metalics and the "warp" goes away. I just know recived the link again from another subaru person after i lost it.

http://www.stoptech.com/whitepapers/...otors_myth.htm

[Andy]

Originally posted by svxsubaru1
I have read this before and have been wanting to post this because it has worked for me on a couple of cars for me when the disc start to "warp" i put on some hard semi metalics and the "warp" goes away. I just know recived the link again from another subaru person after i lost it.

http://www.stoptech.com/whitepapers/...otors_myth.htm

Our discs do warp, usually caused by the wheel nuts being overtightened with an air gun. Simply re-torqueing the nuts will cure the problem, if carried out soon enough. If the problem is left, it becomes permanent, probably due to uneven wear. If this happens, the only cure is replacement.

The problem you have described can occur with some cheap after-market pads but I have not heard of it happening with our OEM or decent pads.

There does seem to be an overheating problem with our brakes, probably caused by the weight of the car. This can manifest itself when stopping from high speeds. Many of us have fitted replacement discs and pads which have cured all of the problems and improved braking performance.

[newsvx]

I have mentioned a number of times in posts that the semi-metalic (like Axxis from Australia) will go a long way toward keeping our rotors from warping. The metalic pads, in fact, wear on the rotor, effectively keeping them "trued up". The fact that the lug nuts have to be evenly and appropriately tightened is also a critical factor - I run about 80 ft lbs. High temp brake fluid is also a must.

Personally, I like the stock SVX brakes (with upgraded semi-metalic pads). I would like to go to the steel braided brake lines for a more firm feel to the petal, but that would move me out of the SCCA G-Stock class to modified. There is no way I could be close to competitive in a modified class.

As for performance, I have run at both Summit Point and Virginia International Raceway and had no problem with brake fade (high temp brake fluide is very much a key to this as well as the hardware of the braking system). At my advancing age, I doubt I push the car more than 7 or 8/10's of its capability, but still, the brakes work really well. I have even had an instructor at Summit Point comment (while driving my car) going into Turn 1 at 115 - 120 MPH, "Wow! This car has brakes!
Harry

Originally posted by Andy


Our discs do warp, usually caused by the wheel nuts being overtightened with an air gun. Simply re-torqueing the nuts will cure the problem, if carried out soon enough. If the problem is left, it becomes permanent, probably due to uneven wear. If this happens, the only cure is replacement.

So how does one re-torque the nuts accurately? My wheels are rotated every service and I'm pretty sure they just use an air gun each time

Thanks

[Andy]

Originally posted by amuse


So how does one re-torque the nuts accurately? My wheels are rotated every service and I'm pretty sure they just use an air gun each time

Thanks

With a torque wrench. (and bollock your garage)

[svxsubaru1]

newsvx so the axxis pads dont have problems on the track with over heating because i want to track my SVX and dont want to run into that.

[newsvx]

Originally posted by svxsubaru1
newsvx so the axxis pads dont have problems on the track with over heating because i want to track my SVX and dont want to run into that.

Never had a problem at all! Track or autocross (back-to-back runs).

Harry

[Jamsvx]

Originally posted by amuse


So how does one re-torque the nuts accurately? My wheels are rotated every service and I'm pretty sure they just use an air gun each time

Thanks

They used air guns on mine too when the tires were replaced but (thanks Blake) we retorqued them ourselves with a torque wrench - about $50 I think - would not need a fancy one since would only need to do once in a blue moon

How are things in Qld???

:-)

[Mr. Pockets]

I keep hearing that over-torquing lug nuts can cause brake rotors to warp. As a matter of fact, I've heard it since before I bought my SVX over four years ago. But I have yet to see an explanation for why this might be true.

Don't get me wrong - I'm not arguing that it will or will not happen, so I don't want testimonies. I want an explanation, please.

[Andy]

The simple explanation is 'Thermal Expansion'

Do you really want the long explanation?

[Mr. Pockets]

Originally posted by Andy
The simple explanation is 'Thermal Expansion'

Do you really want the long explanation?

Nope, that's good enough and what I expected. It's just bothered me that this concept has been accepted as dogma by many without any actual explanation behind it.

Thanks.

[newsvx]

Thermal Expansion is the "action" (normal in any braking system / rotor), and over tightening the loug nuts prevents this expansion in some areas, and allows it in others. The key is that there MUST be some expansion allowed. Further, when lugs are over tightened, the amount of torque on each one will differ, thereby causing different "amounts" of expansion. That causes the "warp of the rotor". And as mentioned earlier in this thread, if the uneven braking resulting from the warp in the rotor is noticed soon enough and corrective action is taken on the torquing of the lug nuts, all is good (usually). However, if it goes uncorrected for long enough, a bad wear pattern sets in making the warp permanent, and the only way to correct it is to turn the rotors, assuming they are not that bad. Of course, by turning the rotors, that makes the rotor thinner and more likely to warp from excessive heat. One of the probelms with modern cars today is that rotors are made as thin as possible - to save on overall car weight (for gas mileage) and to save on unsprung suspension weight (for better handling dynamics). And I won't address "and it is cheaper too".
Hope this helps.
Harry

[Mr. Pockets]

Thank you for the long explanation. Again, it's pretty much what I expected.

Now I wonder how much a rotor actually expands at operating temperature...

[oab_au]

The expansion rate of cast iron is very low,compared to other metals. The over torqueing of the lug nuts causes the top hat section to distort in a wave shape, this is magnified by the time you get out to the friction surface.

The other cause of warping that happens when long hard breaking heats the disk, is because the disk is a sand casting, that is chucked up in a machine, to machine the surfaces.

If the casting is slightly off line when it is held in the machines chuck, the finished disk will have a difference in the amount of metal between the vents and the breaking surface around the circumference of the disk. This causes an uneven expansion and the disk surface will warp when hot. This warping will disappear when they cool down. Thats why some of the SVX s warp disks bad and some don't do it at all.

The later after market disks have a more controlled casting and machining process to keep the disk section even, to prevent warping.

Harvey.

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