Why does the front disk brake warp?

pmansson

pmansson

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All brake components were renewed about 5 years ago.
Total mileage since: perhaps 5000 miles
DOT 4 fluid renewed every 2 years.
No hard driving with excessive braking.

Lately I had the steering wheel beat back and forth on braking, even lightly.

So, I now have new disks mounted and the problem is gone, BUT why did they warp ??
Thanks,
Peder
 
I have been told and always believed that if the rotors are hot and you hit a large puddle that the cold water and rapid cooling can lead to warping. Others suggest that if you hold your foot on the brakes at a stop light with hot rotors the heat sink into the pads may cause warping. Each is plausible, others will have their opinions as well.
 
I agree with the above thought, along with the fact that any metal that goes through thousands of heat cycles is suspect to warping. There's a lot of those little molecule thingies moving around really fast, then trying to find their place again when things cool down. :mrgreen:
 
You guys with the scientific knowledge just amaze me!

hehehe
 
So what we refer to as "warping" is this;

"In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. This uneven deposition results in thickness variation (TV) or run-out due to hot spotting that occurred at elevated temperatures."

The term warped disc is so ingrained in our vocabulary that it will probably never go away. Regardless, turning of the rotor returns it to its original flat shape by removing the deposits.

:)
 
Hi Chris,
so in essence you suggest the deposits that cause the unevenness,will go away on its own after a while...`(by using the brakes as abrasive) ?
 
I have also had a rotor that had a hard spot in it (not on my coupe). From new it was good but well before it hit 10,000 miles it developed a vibration at fairly high speed braking and continued to get worse with increased mileage. I had them turned and within 8,000 miles the vibration with braking at speed came back. That is when I fould out about the hard spot. I could actually see the difference in the material.

These were not cheap rotors and came from a well known racing brake supplier. They told me this kind of thing happens sometimes on even the best of rotors. I was not too happy with them when they would not replace them without a receipt. I didn't think keeping a receipt for rotors that long would be needed. I still buy race brake pads from them but nothing for my street cars.
 
Hard spot... could be!

Forget about nature and dogs. The car never goes in rain, or is washed with water, or parked longtime with the handbrake....

But gwittman´s idea of a manufacturer´s hard spot feels more plausible. My 60 year old Italian tyre shop owner immediately suggested a bad steel/bad forge issue. He has been in this business since the mid 60s. He balances the front wheels of my front heavy 60s Jaguars with the front in the air and wheels in place. Very few shops still have this equipment. It takes into account parts of the front axle when balancing the wheels.

When I talked to the provider of the discs/rotors (in the US?!), he blames the calipers, which he also provided, saying they will only perform 100% when using a silicone brake fluid. I use DOT 4 which I change every 2 years.

I tried silicone on a totally rebuilt Jaguar in 1985, and found them spongy. On an uphill slope, waiting for a red light to turn green, I remember the car would not roll back immediately as I took my foot off the brake pedal.

I know that just about all brake components will have to be replaced, or at least removed and thoroughly cleaned before switching to silicone. So for these 2 reasons I am reluctant to do it.

I have now mounted 2 original, NOS BMW rotors, but am of couse worried about them being damaged by faulty calipers.....

If the culprit was bad rotors, developing a hard spot after a few thousand miles, I ought to be fine with the real stuff.

Problem is I don´t know what caused the shakes in the steering wheel. It happened at all speeds right down to braking from 20 MPH.
 
pmansson said:
I have now mounted 2 original, NOS BMW rotors, but am of couse worried about them being damaged by faulty calipers.....

If the culprit was bad rotors, developing a hard spot after a few thousand miles, I ought to be fine with the real stuff.

Problem is I don´t know what caused the shakes in the steering wheel. It happened at all speeds right down to braking from 20 MPH.
Click to expand...

I don't follow the logic behind blaming the calipers for rotor warpage - unless you had reason to believe the calipers were prone to sticking or seizing. I also question the suggested use of DOT5 silicone fluid as though it would prevent a situation caused by the more common and manufacturer-recommended DOT3-4 fluid.

Since changing the rotors appears to have cured your problem, it is likely that the rotors were the prime culprit/s. It is therefore unnecessary to mention other potential causes of brake shudder, such as tires, wheel runout and suspension setup. However, you did not mention anything about the original friction pad composition or whether the pads were also renewed with the new rotors. Friction materials differ in design and manufacture. Although unlikely, defects do occur and pads can become easily contaminated by improper handling - which may have also contributed to rotor warpage. Similarly, even misplaced greasy fingerprints on pads or rotors might conceivably lead to hot spotting and/or eventual braking issues, although you would have likely noticed the problem from the beginning.

Good luck.
 
The friction pads: yes they were changed with the calipers and rotors about 5 years ago.
They are the best I have on any of my cars. Last set the supplier had. Cause lots of dirt on the wheels, but the best braking I have ever had. Not made anymore. Don´t know if they have asbestos in them (which is no longer permitted).

I too believe the rotors are the culprit, and as my Italian guy said. He is the oldest guy of all technicians I use and talk to. ("Happens all the time nowadays" attitude confirmed this).

I will follow up later.
 
1) Stick with german-made, Zimmermann rotors, I don't not have any problems ever with Zimmermann.
1a) Balo? meh. I just don't know about italian-made brake rotors. Not my idea of a good time.
2) For solid rotors, I ONLY use Metalmaster pads (Repco, PBR, or whatever the current parent company is.) They were THE standard for decades. Yes, they are not easy to find, but you can. Yes, these are semi-metallic. Yes these "chew" rotors.
2a) Rotors are safety-related consume-ables. That means (for me) that after I get 40k+ miles out of a set of rotors I can throw them away, [for me] machining is false economy, they are not that expensive.
3) For vented rotors, I personally stick with metalmasters but there is (I suppose) more latitude for using (what some modern brake experts) call "current technology." It seems everyone wants track-capable brakes, or much more better brakes than were originally engineered for our cars. Funny thing is I have been in a lot of cars that had crap for caliper pads and people paid stupid money for the damn things!.
3a) The only time I accept the upgrade rationalle for a street car is for a 2800 replacing rear drums with discs makes sense. Otherwise, all fresh, all new parts always keeps me happy. And you know how seldom I sound happy ;-)
 
The only time I accept the upgrade rationale for a street car is for a 2800 replacing rear drums with discs makes sense. Otherwise, all fresh, all new parts always keeps me happy. And you know how seldom I sound happy ;-)[/QUOTE]

Re: DP's quote, is there a thread out there explaining that drum to disc conversion, the necessary retrofits, pitfalls, costs?
 
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