Discs always warp

[willmagrath]

Hi all,

Struggling with warping discs. Pretty much every set of discs I've ever fitted have warped.

Fitted new front discs to my MX5 and 300 miles later they are badly warped.

I've done exactly what the manufacturer recommends (usually 300 miles of light braking) and then drive normally.

Anything I might be doing wrong?

Thanks

[rev-erend]

Most discs do not actually warp. It's actually a carbon build-up from the pads which causes a high spot.

Perhaps your driving style encourages this.

If for example you always brake as late as possible as opposed to brake early and coast to a halt you may find things improve.

Maybe you hold on to the footbrake after a high-speed stop. This would allow carbon to steel transfer on a hot rotor.

[GreenV8S]

Check how you're cleaning them before fitting.

If there is any contamination then heat will build up unevenly. This leads to uneven impregnation of the disc which encourages more uneven heating, Eventually the crystaline structure of the hotspots changes, making them harder so they wear less. This leads to a vicious spiral.

Apparently garnet paper can sometimes be used to remove the surface impregnation and get back to clean iron although I've never tried it myself.

Also avoid coming to a stop with the brakes applied and avoid applying the front brakes while stationary when the brakes are very hot - let it roll the last couple of inches and then hold it on the handbrake rather than the footbrake.

[Panamax]

rev-erend said:

Most discs do not actually warp. It's actually a build-up from the pads which causes a high spot.

Where are you buying your discs and pads?

Often the easiest cure for "brake problems" is to fit OEM. They should be correctly matched to the weight and characteristics of the car whereas aftermarket parts are often just a physical fit.

[ARHarh]

With my MX5 the front calipers were stiff and sometimes stuck causing overheating issues, and a judury peddle. Cured by rebuiling the calipers. I have also had similar issues when the slider pins are stuck. so basically go back and make sure all the sliding parts move easily. My MX5 had a history of brake issues before I bought it faling mots for a few years before i got hold of it for brake problems. I guess it had little use for a few years and caused these issues.

[aka_kerrly]

Maybe check the slider pins are fine and you haven't got sticky calipers

[Dal3D]

Check that the bushes near the brakes are OK.
I went through 3 sets of pads and discs only to find the bushes were worn putting more stress through the discs when braking causing them to warp.

[ChocolateFrog]

What brand of discs and pads and where were they bought from that would be my first question.

After that I'd want to know what temp they were getting upto and whether that varied from side to side.

Has it had remanufactured calipers on it etc etc.

[steveo3002]

get a dial gauge on the mounting flange that the disc sits on

[Driver101]

To warp every set of discs and discs within 300 miles is very unusual.

How many miles do you get out of discs and pads?

Is the caliper sticking?

Are you applying the brakes when the car is stationary and the brakes are hot?

[MustangGT]

rev-erend said:

Most discs do not actually warp. It's actually a carbon build-up from the pads which causes a high spot.

This, every time.

[348jeff]

I assume you've felt the wheel/discs after a run and they are not overheating? How old are the calipers? Maybe they are due for replacement. I've just done all 4 on my daughter's MX5 despite them all working they didn't really give a clean sweep on the discs.

When you remove the pads is each worn down to the same thickness or is one more worn than the other? If so it's a good indicator of sticking pads or calipers?

If you look at the pic below when I was comparing a new set of pads with the old you can see that both the inner and outer pads are as thick as each other. Sometimes when you remove the pads one of them is much thinner than the other indicating a problem.



Also, when you put the pads back in (and before you drop the caliper back in place) do they freely slide side to side in the carrier - mine didn't cause a squeak so I had to strip them down and to ever so slightly file down the pad where it contacts the carrier so it moved easily.

[Leveret]

'Most discs do not actually warp.....'

Quite so. They can develop areas of different coefficients of friction which cause juddering. This became a problem from the 15yr old/ 65,000 mile OEM front discs on my Audi A8. I took the wheel off, chocked the other front wheel, handbrake on, engaged 'Drive' and honed both sides of the rotating disc with a carborundum wheel. Sorted.

[tobytronicstereophonic]

steveo3002 said:

get a dial gauge on the mounting flange that the disc sits on

This is going to be the likely cause. Clean the hub face to perfection. Buy a £15 DTI set up from eBay and ensure there is no run-out. Even a pencil on an axle stand will suffice. You have a hub problem.

When a new disc is fitted to a warped or damaged hub, for some reason the car will initially seem fine. Within a few hundred miles, the brakes will judder/pulse and you are back to square one. Honestly, this will be the issue. I've returned multiple discs when it was a dodgy hub all along.

[stew69]

Have you had your wheel’s refurbished ?

[Gary C]

I used to warp my 200SX's disks then I realised it was because I used to brake very heavily coming off the M6 at Lancaster then often sitting at the Lights with very hot disks which then cooled unevenly (ie the bit in the caliper cooled much slower).

Started to brake then roll to the lights allowing the disks to cool and suddenly got a lot more miles out of a set.

Also, cheap disks from Euro carparts etc are cheap for a reason.

[MakaveliX]

I think discs can warp if sat stationary for a while with your foot pressed firmly on the brake pedal.

[944 Man]

Discs almost never warp. You would be surprised how this myth continues though, perpetuated by ‘professionals’ who should know better.

The vibration is caused by a build up of pad material on the disc’s surface. It WILL clear itself but it can take a ridiculously long time in some cases.

[944 Man]

MakaveliX said:

I think discs can warp if sat stationary for a while with your foot pressed firmly on the brake pedal.

At the bottom of an Alpine pass. Certainly it is a thing, but it is pretty rare, even in motorsport.

[Dynion Araf Uchaf]

Are you sure it’s not the ABS kicking in?