Tips to avoid brake vibration?

[Robertb]

I had new front discs put on my CLS 14 months ago, and they gradually started to vibrate slightly through the steering under braking.

I had them skimmed in situ the other day, and now all is well. Pads were not changed (neither the discs nor pads were particularly worn)

Any tips to keep them in good order... do I need to bed them in again?

[ARHarh]

Chances are if they really warped in that time with little wear you have something sticking, causing the brakes to overheat. Just check to see if any brake is hot after normal driving. Properly fitted brakes with plenty of life left do not vibrate unless badly fitted or they are over heating.

It could be tyres or suspension but if it went away after skimming chances are it not that.

[MustangGT]

99% of brake vibration and judder is caused by build up of friction material on the rotor (disk). A series of hard braking manoeuvres should resolve the issue.

[PhillipM]

I'd say 2% is actual warped discs or warp through corrosion on the hub - 30% is pad buildup, and 68% is corrosion on the inner unswept surfaces slowly encroaching on the pad area, certainly almost anything I've changed the past few years has been the latter.

[Dashnine]

If you do a lot of high speed stops, then sit with your foot on the brake (or these days on Auto-hold) the lack of cooling where the pads contact the disc can cause disc warping and hence judder. Junctions at the end of motorway slip roads, roundabouts on dual carriageways, etc.

[Tony1963]

Dashnine said:

If you do a lot of high speed stops, then sit with your foot on the brake (or these days on Auto-hold) the lack of cooling where the pads contact the disc can cause disc warping and hence judder. Junctions at the end of motorway slip roads, roundabouts on dual carriageways, etc.

I doubt that causes a disc to warp.

[Dashnine]

Tony1963 said:

Dashnine said:

If you do a lot of high speed stops, then sit with your foot on the brake (or these days on Auto-hold) the lack of cooling where the pads contact the disc can cause disc warping and hence judder. Junctions at the end of motorway slip roads, roundabouts on dual carriageways, etc.

I doubt that causes a disc to warp.

It did when I worked in Brake Engineering for Lucas / TRW / ZF, admittedly a few years ago now. It was a big problem when asbestos first had to be removed from pad material as it was a good material for transmitting heat away from the pad face.

A lot of the replacement materials couldn’t move the heat and you got a different cooling profile around the disc which resulted in a huge increase in brake judder (which then led to abrasive material in the pads being used which ground the disc judder out and hence why discs and pads never last as long these days and are replaced simultaneously).

Maybe modern pads are better now, but there’s a huge difference in cooling rate between the ‘open’ area of the disc and the pad contact area when a lot of energy has gone into the disc which translates to warping, and if the warping can’t be ground away quickly enough, you get judder again.

Edited by Dashnine on Saturday 20th May 08:31

[Tony1963]

Dashnine said:

It did when I worked in Brake Engineering for Lucas / TRW / ZF, admittedly a few years ago now. It was a big problem when asbestos first had to be removed from pad material as it was a good material for transmitting heat away from the pad face. A lot of the replacement materials couldn’t move the heat and you got a different cooling profile around the disc which resulted in a huge increase in brake judder. Maybe modern pads are better now, but there’s a huge difference in cooling rate between the ‘open’ area of the disc and the pad contact area when a lot of energy has gone into the disc which translates to warping.

About 20 years ago I built a prony rig at work to test the torque output of DC-10 emergency door motors. This rig used a MK2 1.6 Escort brake set up with rev counter and strain gauge.
Left to my own devices, I obviously tested to extremes, and I never warped that puny disc. No cooling air, no let up at all, it just never warped.

I’m sure a lab could set up a particular test to cause any outcome it wanted, but leaving your foot on the brake pedal while at a standstill with hot brakes will, almost every time, transfer pad material to the contact area on the disc. A fraction of a millimetre will be felt.

[Pica-Pica]

I had a build up corrosion and scoring on my discs, through lack of use and salt gritters. The discs cause a vibration. I tried the repeated stops trick, but nothing. As the fronts were low-ish, I replaced them and the pads. A bit better, but I could still feel vibration from the rears. Changed rear pads and discs, vibration went. Lesson learned?, to keep discs clean by braking, I usually drive smoother than that, so I make sure I brake more eg., on downhills.

[E-bmw]

Dashnine said:

Tony1963 said:

Dashnine said:

If you do a lot of high speed stops, then sit with your foot on the brake (or these days on Auto-hold) the lack of cooling where the pads contact the disc can cause disc warping and hence judder. Junctions at the end of motorway slip roads, roundabouts on dual carriageways, etc.

I doubt that causes a disc to warp.

It did when I worked in Brake Engineering for Lucas / TRW / ZF, admittedly a few years ago now. It was a big problem when asbestos first had to be removed from pad material as it was a good material for transmitting heat away from the pad face.

Sorry to disappoint your theory but asbestos is actually an extremely good heat insulator & that was where many of its uses came from.

[MustangGT]

PhillipM said:

I'd say 2% is actual warped discs or warp through corrosion on the hub - 30% is pad buildup, and 68% is corrosion on the inner unswept surfaces slowly encroaching on the pad area, certainly almost anything I've changed the past few years has been the latter.

We were talking about relatively new rotors. If a car is used regularly and the brakes (calipers and pistons) are in good condition then corrosion should not be an issue.

[Robertb]

There was no 'warping' as far as I know, the discs were true and the skimming only removed a tiny amount of the disc faces. Its certainly done the trick so far, hopefully the vibration won't return, though it took a good 6000 or so miles previously to begin to manifest when they were new.

As mentioned above, I also wondered if stops from motorway speeds then waiting at junctions could cause issues over time as you leave the hot disc/pad in contact while you are sitting with the brakes on. Or perhaps the 1km 15% downhill with traffic lights at the bottom on my commute. Then again, pads sit so close to the disc surface anyway even when not applied I can't see it making much difference in road use.

[TwinKam]

Robertb said:

There was no 'warping' as far as I know, the discs were true and the skimming only removed a tiny amount of the disc faces. Its certainly done the trick so far, hopefully the vibration won't return, though it took a good 6000 or so miles previously to begin to manifest when they were new.

As mentioned above, I also wondered if stops from motorway speeds then waiting at junctions could cause issues over time as you leave the hot disc/pad in contact while you are sitting with the brakes on . Or perhaps the 1km 15% downhill with traffic lights at the bottom on my commute. Then again, pads sit so close to the disc surface anyway even when not applied I can't see it making much difference in road use.

This is what you have a hand ('parking') brake for. Granted, manufacturers have made it increasingly difficult to use short term (or is it just terminal laziness/ignorance of the driver?) as manifested by the almost universal in-your-face-glare of brake lights at junctions and traffic lights etc... my personal top pet hate... so no offence but yes I really do want to believe that this dreadful habit does warp discs

[MustangGT]

TwinKam said:

This is what you have a hand ('parking') brake for. Granted, manufacturers have made it increasingly difficult to use short term (or is it just terminal laziness/ignorance of the driver?) as manifested by the almost universal in-your-face-glare of brake lights at junctions and traffic lights etc... my personal top pet hate... so no offence but yes I really do want to believe that this dreadful habit does warp discs

Problem with that is that all auto cars, that I know of, the stop/start needs your foot on the brake to work.

[TwinKam]

MustangGT said:

TwinKam said:

This is what you have a hand ('parking') brake for. Granted, manufacturers have made it increasingly difficult to use short term (or is it just terminal laziness/ignorance of the driver?) as manifested by the almost universal in-your-face-glare of brake lights at junctions and traffic lights etc... my personal top pet hate... so no offence but yes I really do want to believe that this dreadful habit does warp discs

Problem with that is that all auto cars, that I know of, the stop/start needs your foot on the brake to work.

Well 'Stop/start' should be deactivated the moment you start the car, hateful wasteful damaging concept. But I agree autos are a faff regardless, due to the interlock procedure of selecting D from N, and don't get me started on foot operated 'hand' brakes...
Regardless of the car, it is good practice to be in neutral with 'hand' brake not foot brake applied when stationary for anything more than a few seconds, and manufacturers are not facilitating this ...even VAG's handy 'brake hold' feature applies all the brakes... [/rant]

[Pica-Pica]

MustangGT said:

TwinKam said:

This is what you have a hand ('parking') brake for. Granted, manufacturers have made it increasingly difficult to use short term (or is it just terminal laziness/ignorance of the driver?) as manifested by the almost universal in-your-face-glare of brake lights at junctions and traffic lights etc... my personal top pet hate... so no offence but yes I really do want to believe that this dreadful habit does warp discs

Problem with that is that all auto cars, that I know of, the stop/start needs your foot on the brake to work.

No. On my F30 ZF8, stop/start will work if P is selected, you can then take your foot off the brake pedal. You can use the manual parking lever then if you wish. Although I prefer to be in N and parking brake applied (thankfully a proper lever).

Edited by Pica-Pica on Monday 5th June 23:24