[Closed] So, why does my car keep warping front discs?

Thinking about it, I may be guilty of sitting on the brakes at the lights occasionally, that's a bad habit I used to have so it might still happen, but I'm not hard-stopping beforehand

I'd guess it's this, there's a lot of heat being insulated into a small area of disc which the pad contacts even if you haven't stopped in a big way, just stopping a car generates a lot of heat.

I notice it quite a bit in borrowed or hired automatics I've driven - I guess the tendency to hold on the brake pedal is even higher.

is there run out in the hub? if so, then if you bolt new disks on they will run out and could cause judder

I'd hazard CP is correct, that's a ludicrous amount of pads to go through in that millage, Google how to bed pads in, (in a nutshell you just get the brakes up to temperature and then do about 10 emergency stops) but essentially, if you keep your foot on the brake at a standstill when the disks and pads are hot, you will get an uneven lumpy feel as the pad material will transfer to the disk.

So I'd guess your disks are not warped at all, you've just got an uneven layer of pad material baked onto your disk.

Have you actually measured the disc run out? It's just that my car demonstrates all the symptoms of warped discs but it's worn front suspension joints. (E39 Bimmer - known issue).

I doubt cp's suggestion. I've got two automatics, I always have my foot on the brakes at junctions, and they don't warp.

Either it's the hub faces or something else out of whack, as per hamish. You can measure hub run-out using a run out gauge, and the stand for it, available from places like Machinemart. I have one I'd lend you but I don't think you're local enough.

" doubt cp's suggestion. I've got two automatics, I always have my foot on the brakes at junctions, and they don't warp."

and my mother manages to cause a warped feeling on every auto(big heavy cars) shes owned by the brakes being hot and her holding her foot on them at junctions/in traffic.

transfer of material onto the disk face creates a grippy area.

Is that not just one of those theories that turn into things every DIY mechanic 'knows'. and then when you google it it comes up all the time because everyone 'knows' it? It certainly seemed very disputed when I last googled it.

Why are folk sitting with their foot on the brakes at junctions anyway? Don't they teach proper driving these days?

whats your (amateur mechanics) theory for merc AMG and range rover disks juddering uncontrolablly every 8-10k with my mother driving then - oh and it stopping happening since my dad taught her not to hold her foot on the brake - could be coincidence i guess.

Sit on the brakes at lights.

they dont know how the gear stick works .

I had a similar issue with a Peugeot 306 td.
I'd brought some good pads that were supposed to give off less dust. The discs seemed to warp within 12 months, I changed to some cheap bog standard pads and never suffered the problem again. To be fair though it does seem you may have already tried this.

Could be pad resin left on the discs which is often mistaken for warped discs as it creates high spots. Try warming the brakes up then doing a series of hard stops. Any resin on the discs will soon come off.
Hub run out can give the effect of warped discs too but you would normally feel that with new discs too. I've already assumed you will have cleaned the hubs up prior to fitting new discs.
I'd out my money on resin build up which I used to get with the ST225 upgrade on my Mondeo and that was from hard braking then leaving my foot on the brake whilst stationery. Had the same thing on the Octavia that the dealer wanted to replace the discs and pads to cure but some very hard braking soon got rid of it.

if you keep your foot on the brake at a standstill when the disks and pads are hot, you will get an uneven lumpy feel as the pad material will transfer to the disk.

Cheers folks, very helpful so far!

Hmmmmm. Working with the idea of it being pad material transfer rather than actual runout... Is the only diagnosis tool there to measure runout? Or could I, I dunno, go through a break in cycle and see if it changes?

<edit- CraigXXL posted since I started typing this. I'll go and terrorise the industrial estate tomorrow, nothing to lose after all>

It doesn't [i]feel[/i] like a grabby point on the disc- in slow braking there's no obvious pulses. I've had that before (it did it when I got it) and it was fairly noticable. Though, doesn't rule it out at all.

hamishthecat - Member

Have you actually measured the disc run out? It's just that my car demonstrates all the symptoms of warped discs but it's worn front suspension joints. (E39 Bimmer - known issue).

Haven't measured run-out but replacing the discs removes the issue so it's definitely brake related. It's had all new front suspension parts in the front about 5000 miles ago. (broke a spring but it made no sense to only change the springs as everything else was so tired so basically the hub knuckles are original, everything else from suspension tops to arms went in the bin)

Maybe I'm wrong but I'm doubting hub run-out simply because with new discs and pads, the symptoms go away- I get several thousand miles trouble free then they return. That's not how I'd expect a permanent misalingment to manifest? Though, it could be stressing the parts in some unnoticable way that only shows up after a lot of cycles...

OTOH, I own a dial gauge and I could easily fab up something to measure this- I see the tools for sale are basically a clamp and a bendy arm. So that'd make sense to do

scotroutes - Member

Why are folk sitting with their foot on the brakes at junctions anyway?

To be fair, I'm not sure I do. Certainly not often- maybe occasionally in stop start. But I know I did it in the past so it's possible. When I was thinking about causes, it came back to mind but it's a bit of a reverse engineered explanation if you know what I mean.

But, driver input seems like a really obvious place to look, since the mondeo's not especially known for this. I suppose that's the other diagnostic- put a new set on it and be damn sure I'm not doing anything stupid.

TBF, my comment was more aimed at the idea that this is so common it's all over the Internet.

So why doesn't every automatic car have warped disks?

Because they put it in park when stopped rather than standing on the brakes in drive?

Or they're all driven by folk who never go fast enough to generate hot discs

A friend of mine had 3 sets of discs warp. Eventually (as he explained it to me) he found out that that the wrong wheel bearings had been fitted, so that there was play between wheel and axle, and the discs were all that held the wheel straight. I find it hard to believe, and only mention it because it illustrates that sometime the cause is not obvious.

Cheers greybeard- it's had new front bearings in this period so I'll rule that out but that's exactly the sort of thing I'm after

Don't brake hard and hold the brake at the top of slip roads. This stops the brake cooling where the pad is and it deforms. Release the brake after a hard brake allow the disc to rotate freely. Brake early and allow the disc to cool without holding it clamped on.

Do you wash the car.....I had similar symptoms where it was something to do with the wash/wax stuff used in the jet wash contaminating the discs.....it left a clean patch when it was parked gave a similar sensation to minor warping of the discs. Once I realised and stopped doing it, cleaned the discs the issue stopped.

Suggsey - Member

Do you wash the car

Sometimes as often as twice a year. (I always figure that while dirt isn't an MOT matter, the mechanic might not like it if he gets dengue fever when he touches the seat)

Maybe I'm wrong but I'm doubting hub run-out simply because with new discs and pads, the symptoms go away

Sonic it builds up over time, how come it builds up in the same spot? If it takes a long time then it would only be a small amount of material each stop. Consequently, you expect that to average out all round the disk no?

I don't put the car in park at lights, I do not have pulsing discs.

"I don't put the car in park at lights, I do not have pulsing discs"

you have light cars that you drive like miss daisy ?

molgrips - Member

If it takes a long time then it would only be a small amount of material each stop. Consequently, you expect that to average out all round the disk no?

Good point. But, it's not a sort of linear thing like a gradual buildup as you visualise, it's more like "aargh a thing went wrong" then a while later "aargh another thing went wrong/the original thing went more wrong"

Sometimes as often as twice a year.

it's got leather seats, leather doesn't rot for ages.

That's eliminated that then 😆

IIRC, warping would be mostly due to excessive heat build up and hard breaking whilst the discs were of a high temperature.

So possibly other things to consider might be to check if there are any brake ducts in the front apron that are blocked or closed off, or indeed not there because at some stage it's had a new apron fitted from a lower powered model.

Performance pads are designed and made to run at higher temps, whilst the standard discs are not, have you mixed the harder compound pads with stock discs?

Are the caliper sliders well greased and running free? Are the gaiters present?

Have your previous replacement discs been from the same manufacturer? Perhaps they are just made from low cost steel and not up to the task for your model?

A few really basic questions, but it would seem that it's going to be something obvious rather than anything else.

I confess to not having come across the holding the brake pedal down reason before, but I guess it's as much down to driving style as well.

you have light cars that you drive like miss daisy ?

I don't have this issue and I drive a heavier car than the OP, with an auto box and often stop at junctions with my foot on the brake. I do drive fairly gently though...

[i]Because they put it in park when stopped rather than standing on the brakes in drive? [/i]

Eh, I take it you don't drive an auto - park is for parking, not pausing.

Also, using the brakes (lights) means you're very unlikely to be run into from the rear.

All good thoughts. No venting /ducting in these models- it's basically an ST155 so a warm family car rather than high performance 😆 I'm just pretty aware that you get the exact same brakes on every mondeo from bottom to top so that could expose weaknesses, but at the same time people complain of lack of performance but not outright issues. I've had EBC reds in it in the past but the last 2 sets of discs/pads were mintex and pagid boggo pads and discs, matched sets.

The sliders are all pretty happy and like i say I don't think the calipers are binding- I've never found any sign of unusual heat, not to say it never happens but if it does, it's not been there when I've checked at end of drives etc. Plus if there was a significant dragging or binding issue I'd expect to see that in pad wear, no?

If new discs cure it, then it's most likely a run out issue.

New discs have a nice continual thickness, but if they're not running true, you get very slight rubbing at the high/low points. That very slight rubbing leads to uneven wearing/thickness, which is what causes the juddering. It doesn't take much variation in disc thickness to cause a judder.

10 minutes spent with a dial gauge and micrometer should highlight what the problem is, and what the cause is.

Discs given a thorough de grease before being fitted / driven?

I watched Quickfit monkeys take discs out of the box, and whack them on a car and throw the grease covered brown packing paper in the bin.
Wheels on and your good to go ( and warp your discs possibly )

Point taken OP and as you say, if the caliper said were binding, you'd notice heat and a reluctance for the car to roll too.

Looks like mc and others who are suggesting hub / disc run out are closer to the mark. 🙂

I doubt very much that you have warped discs.

When you attach the wheel and do up the wheel nuts, do you do them carefully in a star pattern, and torque them up? Or how do you do it?

For using the dial gauge you can get a magnetic clamp arm thingy which helps.

This may help - I started to experience a judder so I did a series of hard stops, accelerate, hard stop and repeat on a quiet industrial estate and that 'cleaned' the surface. Everyone told me the discs were warped. They weren't slhot spots had created 'zones".

Try it-0-60-0 and repeat.

mc - Member

If new discs cure it, then it's most likely a run out issue.

New discs have a nice continual thickness, but if they're not running true, you get very slight rubbing at the high/low points. That very slight rubbing leads to uneven wearing/thickness, which is what causes the juddering. It doesn't take much variation in disc thickness to cause a judder.

Ah OK, that makes a lot of sense- the way I was coming at it, it didn't seem to add up but this is another route to the same result. Cheers!

maybe I use them a little harder than typical

No offence intended by my thoughts below but if you are warping the discs (as opposed to the other problems suggested above) then you need to consider for they are getting that hot that they'll warp...

Do you use them forcefully a lot?
Do you carry a lot of weight?
Do you sometimes use them hard from high speeds regularly in short succession?

I've got a mk3 diesel wagon and it's nowhere near that hard on its brakes.

My old 306 gti I could warp a set of new discs in about twenty minutes if I tried hard enough - on track.

The cause of the warping with that car was lots of sudden, hard decelerations without adequate cooling time between each use of the brakes. It has sweet fa to do with total miles driven.

If you are regularly hammering the car on twisty A roads or have a habit of being hard on and off the brakes and throttle at high motorway speeds (eg keep going down from 90-50 with the brake pedal on the carpet) then it's conceivable you'll be putting a lot of heat through the system but enough to warp three sets of discs would I guess take some serious abuse.

The brakes on the mark 3 are adequate but they're not designed for really hard driving / repeated hard use.

Nah, nothing like that- like I say, just a little harder than might be average, but not frequent heavy use.

could it be something to do with the abs. probs not though if it stops with new disks.had the pulsing brake thing on a old n reg 306 sedan many years ago after the rear axle was changed cant for the life of me remember how i fixed it. sure it was abs related though.

Used to get this on a Pug 206. Was going through a new disc per main service! Okay the service interval is two years, except it isn't as you do an interim service for oil change. Someone suggested this is part of the problem as the service intervals are done to keep the fleet market happy and they put harder pads in to keep it going, but these are warping the discs.

Don't know if that's true, but something was wrecking them. Don't think it's a heavy foot or my car washing regime (or lack of) as hadn't had this with cars before the Pug and not since. Honda Civ now and not changed the discs in 7 years.

cp - Member
I notice it quite a bit in borrowed or hired automatics I've driven - I guess the tendency to hold on the brake pedal is even higher.

I've found this too with hired automatics. I've mainly only driven them in the US, but frequently they've had this. Especially the SUVs and 4x4s. Tends to be on ski trips and coming down from mountain elevations I think people are sat on the brakes a lot.

OK cool, thanks folks, pretty clear courses of action then. Ta!

Having had the last person to change the pads on my Mazda 6 not check the sliding pin seals were in place and having just had to get a blowtorch on the carrier holder to get the pins free again; I do sympathise Northwind. Replacement cariers (no pins, seals or calipers) are £240 each from Mazda!!!

I had original discs on a Zetec Mk3 at 75k.

Never warped them after braking late and sitting at the lights.

Had problems with the rear calipers sticky handbrake - never bought a Ford again.

stopped rather than standing on the brakes in drive?

konabunny - Member
No-one puts a car in park while waiting at the traffic lights. You're not even meant to.

Not what I was taught. At least not if stopped for any duration. Plus I learnt to drive in a very hilly and steep road area so handbrake hill starts at traffic lights were a necessity.

Anyway, on lighting - https://www.gov.uk/guidance/the-highway-code/general-rules-techniques-and-advice-for-all-drivers-and-riders-103-to-158

[I]In stationary queues of traffic, drivers [b]should[/b] apply the parking brake and, once the following traffic has stopped, take their foot off the footbrake to deactivate the vehicle brake lights. This will minimise glare to road users behind until the traffic moves again.[/I]

Note 'should'. Advisory, not mandatory.

Plus I learnt to drive in a very hilly and steep road area so handbrake hill starts at traffic lights were a necessity.

konabunny - Member
Did you learn to drive in an automatic?

Fair enough, no. Just realised previous comment was referring to automatics. Even then though, the highway code...

Actually, was driving an automatic in San Fran on those steep hills and I'd either sit on the foot brake or would use the equivalent of the handbrake (often a pedal) if a long wait in a queue.

Why are folk sitting with their foot on the brakes at junctions anyway? Don't they teach proper driving these days?

Seemingly not, no. Last few folk I've heard of have been taught to use the foot brake rather than hand brake. No idea why as if you get rear ended then its instant loss of control and you are liable for anything you hit.

Seemingly not, no. Last few folk I've heard of have been taught to use the foot brake rather than hand brake. No idea why as if you get rear ended then its instant loss of control and you are liable for anything you hit.

If you get rear-ended the hand brake isn't going to do much to stop you moving because it only acts on the rear wheels.

Try this, NW:

Take the wheels off and (carefully) give the surfaces of the brake disc a very thorough clean. Use wire wool and brake cleaner. You should (hopefully) feel the surface become smoother as you work, and the wire wool will grip less.

Give that a final clean with brake cleaner and a clean rag.

Now, offer a wheel up to the hub. Put the top wheel nut in, give it a few turns to hold it, then do the same with the rest. Try and make it no more than 4 full turns.

Then, going round in a star pattern, turn each nut twice. Keep going round until you feel the bolts bite the wheel itself. This bit won't take long.

Finally, get your torque wrench, set it to the manufacturers torque settings for the nuts, and (still in a star pattern) start at the top, turn each but once, and keep going round until the torque clicks. Don't be tempted to give it an extra turn for luck- just leave it at that.

Thats it. See if that helps.

chiefgrooveguru - Member
If you get rear-ended the hand brake isn't going to do much to stop you moving because it only acts on the rear wheels.

The reasoning is that if you get rear-ended with your foot on the pedal your foot may slip releasing the brake and then you shunt the guy in front, and not only you are liable but it's a bigger accident. Hand brake and car might move but will still be on the brake. Might still hit the car in front with enough force, but you aren't liable.

I think the reasoning behind the advice about keeping footbrake applied at lights is so that brake lights are on and may alert the half asleep tosser who is about to run into you that you have brakes on and may be stopped.

(As an aside, if someone runs into that back of you with enough force to dislodge your foot from the brake, I think I would rather roll into the car in front and help dissipate the energy of the crash to protect my occupants)

I think the reasoning behind the advice about keeping footbrake applied at lights is so that brake lights are on and may alert the half asleep tosser who is about to run into you that you have brakes on and may be stopped.

It's 15yrs now since MissT was taking driving lessons. When I questioned her on why she didn't pull the handbrake on the answer given was that she had to be ready to move off when the lights changed without holding up other drivers 8O. Traffic lights around hear certainly seem to change faster than they used to, I'm more concerned about stopping distances when approaching lights and being rear ended if I stop on orange!!!!

If I suspect someone is approaching me at speed I will just give the brake pedal a couple of taps rather than sit with foot on pedal.

Because they put it in park when stopped rather than standing on the brakes in drive?

I've lived in the USA for nearly 3 years. 90% of friends drive automatics. 100% of them never use the foot brake and never put the car in park unless they are parking the car.
None of them have had warped discs, despite having heavy cars and it being hot a lot.

Someone in a car park reversed into me a couple of weeks back as I was waiting to pull onto the road. I had the handbrake on. If I'd had my foot on the brake instead, and my foot had come off due to the impact, then I could have been catapulted into the traffic on that road. That would be a road with trucks, buses and fast moving traffic.

I like driving threads 😀
But then remember I miss Surfmatt 😥

scotroutes - Member

Someone in a car park reversed into me a couple of weeks back as I was waiting to pull onto the road. I had the handbrake on. If I'd had my foot on the brake instead, and my foot had come off due to the impact, then I could have been catapulted into the traffic on that road. That would be a road with trucks, buses and fast moving traffic.

"...and that's why Northwind's discs keep warping"