Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Doctor Gollum]

out of interest assuming they are unevenly worn not warped by heat,  what is it about expensive discs that stops it happening?

and what prevents it ever wearing back to flat?

i had thought TRW were a good brand.

You're assuming that they were true to begin with...

Quality control and machining processes, or lack there of are both compounded by holding the brakes on whilst stationary. Heat soak will kill any disc, but cheaper grades will be more susceptible,  especially if combined with slightly sticky calipers/pads.

[Magwheels]

Not all metals are made equal! Some are better at certain jobs than others. Metals are made from various ingredients (ie an alloy) and not all manufacturers take the time and effort to get it right for the application it is put in too, that and poor quality control. Hence all sorts of things fail when they really shouldn't. Metals also age and that can make the metal move, that's why decent engine builders/tuners prefer a used block as a base....its "settled".

Still its an easy fix....two new discs.

[Entwood]

Discs very, very rarely actually "warp", as in "bend" .. what actually happens is the surface of the disc gets overheated locally, as an example, you brake really hard then leave your foot on the brake ready for the next get away .. the point of contact of the pad/disc does not cool down, in fact it gets hotter as the heat is transferred from the pad to the disc. This does two things, it transfers friction pad material to the rotor causing a "high spot", and it causes a change in the underlying metal, from cast iron to cementite. This wears at a different rate to cast iron as it is harder, and it also cools slower which makes the problem worse.

Even refacing the rotor will do no good as the high spot might be removed but as the underlying structure of the disc has changed, the problem will recur.

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

http://brakeperformance.com/inspecting-brake-rotors.php

[johnnydog]

Discs very, very rarely actually "warp", as in "bend" .. what actually happens is the surface of the disc gets overheated locally, as an example, you brake really hard then leave your foot on the brake ready for the next get away .. the point of contact of the pad/disc does not cool down, in fact it gets hotter as the heat is transferred from the pad to the disc. This does two things, it transfers friction pad material to the rotor causing a "high spot", and it causes a change in the underlying metal, from cast iron to cementite. This wears at a different rate to cast iron as it is harder, and it also cools slower which makes the problem worse.

Even refacing the rotor will do no good as the high spot might be removed but as the underlying structure of the disc has changed, the problem will recur.

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

http://brakeperformance.com/inspecting-brake-rotors.php

On the subject of so called warped front discs - I do recall referring to this subject in the past? Officially, there is no such thing as warped discs (it's not me that makes this statement, but specialist brake manufactures) - invariably it is a build up of friction pad material that that transfers from pad to disc when hot, especially when the pads are 'clamped' to a hot disc i.e. when sitting at traffic lights with an auto with your foot on the foot brake, which results in high spots around the disc. As the brakes are used, any individual high spots get bigger and eventually cause a kicking through the pedal, more noticeable under gentler braking. People immediately confuse this with warped discs. It can also be caused by contamination behind the hub face and rear of the disc, especially if they have had a smear of copperslip when fitted - they should be fitted clean / dry.  The kicking can sometimes be resolved by a systematic process if firm brake applications - the process is quite detailed, and is also a process for bedding in brakes for more 'spirited' driving.
You may wonder why I say all this. If you google Audi RS4 brake judder, there is a wealth of information on the RS246 forum, from owners (and from myself) about the issues encountered and the technicalities from racing / brake manufacturers.
I know Omegas are a different kettle of fish from an RS4, but the basic principle is the same.
If nothing else, may provide interesting reading before you start giving the supplier of your discs both barrels.....

+1 ....exactly.......

[TheBoy]

Even if the materials were identical (but they're not), but the manufacturing process, including the heat treatments, are different, you'll end up with wildly different quality discs.

TRW are a cheap, nasty brand.

[TheBoy]

Even if the materials were identical (but they're not), but the manufacturing process, including the heat treatments, are different, you'll end up with wildly different quality discs.

This is why, after warping a set of discs, after skimming, sometimes they sometimes are able to withstand a bit more abuse before warping again.


(Using "warping" to mean any defect resulting in a pulsating pedal)

[omega2018]

an update on this.  the vibration was quite bad - the steering wheel shaking on a hard brake. after a  a long period of gentle braking and a few bits of lightly applying the brake while holding down the accelerator, the problem has almost gone away.  it was barely noticeable today on a motorway drive.