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Old 30-03-2006   #1
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Warped discs

hi guys,
just took me uno in to the garage for an oil change and to change the front brake pads. Mechanic told me I have to change my discs as well as they were warped. My quesion is....what causes warped discs and also, should I expect warped discs at just 58000km???

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Old 30-03-2006   #2
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Re: Warped discs

I think Heat normally caused warped discs. Modern discs are softer due to the removal of asbetsos so potentially warp easier. Often made worse by people stilling at lights with the brakes on instead of using the handbrake.
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Old 30-03-2006   #3
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Re: Warped discs

how can staying on the brakes be bad at the lights? I mean there is no wear being generated when stationary!! Am I right in saying so!? Wear is generated when the disc is turning ie when the car is moving. WHen stationary and u use the brake there is no wear on them!
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Old 30-03-2006   #4
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Re: Warped discs

add heat to the equation brake pads pushing on very hot discs
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Old 30-03-2006   #5
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Re: Warped discs

I thought you said your brakes were warped not worn? You brake and pull upto the lights, there is a considerable amount of heat which is trapped in by leaving your foot on the pedal.
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Old 30-03-2006   #6
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Re: Warped discs

58K out of a set of disc's fitted new ones to the rally car, 5k miles ago and when i change the current pads i will have to change the discs as well !!!!

All correct about stopping braking with the brakes kept on easy way to warp the discs, Warping is caused by excessive heat either through a sticking caliper or as said about keeping foot on brake when brakes are hot as the pads stay hot and keep that part of the disc hot whilst the rest heat up. Also driving in to fords (water splashes not the car type) with hot brakes can also cause this.
Perhaps this is why my brakes don't last, 3k out of a set of pads and probably 6k out a set of discs. At least the uno discs and pads are cheap
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Old 30-03-2006   #7
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Re: Warped discs

I do not argue with anything said above, but the simplest reason for discs warping is that the discs are just... worn. See Haynes BOL for their thickness, if memory serves right, the limit value is 9,7 mm.
The new discs are not expensive and unless the old ones are rust-welded in place, their change for new ones is about 20 minutes job per brake.
Hint: Brembo discs have two holes drilled in them to warn you about the need of their change (I hope it goes without saying that I do not have any shares in the company ).
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Old 31-03-2006   #8
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Re: Warped discs

hi guys,
another problem has cropped up. I had just fitted the new brake pads and discs right! (well not me the mechanic). Now all of a sudden after doing around 10 miles and I turn the wheel fully to the left I hear a sort of binding noise and the car stops on its own as if I am applying the brake.

Before you say anything yes I do have alloy wheels with 185/55/14R but there is no rubbing as I checked. Any ideas as to what it could be. The noise is coming from the front left wheel!!
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Old 31-03-2006   #9
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Re: Warped discs

Re: the warped discs... quite often, people do not take the time to check for disc runout when fitting new discs... The official process involves a dial test indicator clamped to the caliper bracket. This is a bit over the top IMHO - it's very nearly as effective to hold a pencil where the brake pad would go, and turn the disc by hand. You can soon see any run-out (even fractions of a millimetre).

What you do next is you undo the 2x 12mm bolts holding the disc on, turn it through 90 degrees, and re-fasten. Check the run-out again. Usually you can effect an improvement because the errors of the hub and disc cancel out. This has worked a few times for me...

You should also clean up the hub with sandpaper to ensure that the disc mounting surface is flat and true.

Now, Drinu, while you're doing all this, check that the disc is centered within the caliper carrier bracket? I fear that the wheel bearing may be loose...

-Alex
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Old 31-03-2006   #10
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Re: Warped discs

Incorrect or uneven wheel bolt torque can cause warpage. Ive seen discs warped in 10,000km. General use will warp discs too.

Check for runout like Alex says. By eye is ok. If any is detected clean all surfaces and recheck. If its still bad, you have to machine the new disc on the hub, or replace the hub.
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