Viewing 40 posts - 1 through 40 (of 62 total)
  • So, why does my car keep warping front discs?
  • Northwind
    Full Member

    I’ve put 35000 miles on it and this is juddery set #3, which is pretty silly. There doesn’t seem to be any obvious cause- I don’t think either caliper is sticking, there’s no excess heat and the pad wear is pretty normal and even… It’s a 2.2 mondeo mk3, so is it just that it’s a big car with a bit of bonus engine and merely adequate brakes? I don’t drag the brakes, maybe I use them a little harder than typical but not drastically, and the car gets driven often so there’s no corrosion build up. 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’ve tried pagid and mintex, and a couple of different pads, on the off chance that I’d just got crap parts. I’ve got the option of sticking ST225 brakes on it for a caliper and rotor upgrade, and it’s not drastically more expensive than feeding it discs and pads is…

    Maybe I just need to get it exorcised…

    cp
    Full Member

    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.

    porter_jamie
    Full Member

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

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    mattyfez
    Full Member

    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.

    hamishthecat
    Full 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).

    molgrips
    Free Member

    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.

    trail_rat
    Free Member

    ” 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.

    molgrips
    Free Member

    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.

    scotroutes
    Full Member

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

    trail_rat
    Free Member

    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.

    hora
    Free Member

    Sit on the brakes at lights.

    trail_rat
    Free Member

    they dont know how the gear stick works .

    pocketrocket
    Free Member

    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.

    craigxxl
    Free Member

    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.

    konabunny
    Free Member

    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 why doesn’t every automatic car have warped disks?

    Northwind
    Full Member

    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 feel 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.

    scotroutes
    Full Member

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

    thisisnotaspoon
    Free Member

    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?

    scotroutes
    Full Member

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

    Greybeard
    Free Member

    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.

    Northwind
    Full Member

    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

    Inbred456
    Free Member

    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.

    Suggsey
    Free Member

    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.

    Northwind
    Full Member

    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)

    molgrips
    Free Member

    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.

    trail_rat
    Free Member

    “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 ?

    Northwind
    Full Member

    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”

    bails
    Full Member

    Sometimes as often as twice a year.

    Whether it needs it or not?

    Northwind
    Full Member

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

    Suggsey
    Free Member

    That’s eliminated that then 😆

    slackalice
    Free Member

    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.

    jamj1974
    Full Member

    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…

    br
    Free Member

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

    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.

    Northwind
    Full Member

    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?

    mc
    Free 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.

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

    singletrackmind
    Full Member

    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 )

    slackalice
    Free Member

    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. 🙂

    codybrennan
    Free Member

    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?

    molgrips
    Free Member

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

    hora
    Free Member

    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.

Viewing 40 posts - 1 through 40 (of 62 total)

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