warped discs - again 2004 E53 3.0 D

[X5-D-Sport]

Exactly the one....
this is the same kit of parts I did my front callipers with.
I also did the rears too... as they all drive the same mileage 

[Smeeagain]

So two questions

What can cause the pistons to stick?
You mentioned the discs warping as it heats up - is it possible that if I fix the sticking piston that the disc will then be fine (I appreciate you havent see the discs and they maybe be fubar but just asking if it is possible that they might be ok after sorting the piston?

R

[Raj]

[quote="Smeeagain"]
So two questions

What can cause the pistons to stick?
You mentioned the discs warping as it heats up - is it possible that if I fix the sticking piston that the disc will then be fine (I appreciate you havent see the discs and they maybe be fubar but just asking if it is possible that they might be ok after sorting the piston?

R
[/quote]

Check it's definitely sticking first. If it is then if you try to free spin the wheel when jacked up it will bind. Also the disc will show signs of burning in terms of a blue tinge to it normally as it gets overly hot.

[Smeeagain]

so if it isn't binding it is just the disc has warped after only a month? Only seems to happen when it is hot ie after repeated braking?

[X5-D-Sport]

Mmmm OK....
lets throw another spanner in the works here....

its often possible that when you jack the car & spin the wheels... all will seem ok !!

You did mention that it is specifically a noticeable issue on a longer journey...
so...
if the disk is permanently warped & buggered, it give symptoms on long or short trips...
The juddering on a longer journey hints at binding calliper, which may need a few jabs of the brakes to get the cycle going...

so, for the sake of simply getting to the bottom of this in one fell-swoop...
get your butt in the car, take it for a run... on a clear long road, gently feather the brake pedal & apply throttle to compensate at the same time... ie .. deliberately heat up the brakes.... untill you get the judder...

keep going another mile or so as normal driving & then pull over & stop.
just by touching the wheel around the area of the wheel bolts, you will likely find one wheel centre is significantly hotter than the other.. and you may even smell the hot pads & disk too...
Et Voila... the hot one is the binding unit..

normally caused by a small amount of rust/corrosion around the piston bore or a minute leak/ vapour of brake fluid causing corrosion again, that will bind the piston to the bore and not allow it to move freely.

the simple fact it happens on a longer journey hints strongly at binding pistons/callipers.

get the kit you spotted & simply fix it - problem solved.

[briankerrys47]

My two penneth,my rear O/S calliper stuck sent message 'check brake linings' sprayed all callipers  with WD40 let  it soak overnight eased o/s pads off prob cured but will replace pads soon.As said touch discs and you will find the 'hot one'

[storminmike]

There are other "sliding parts" in the brake calipers that might not "slide"

When I've done discs and pads I've always paid special attention to the guide pins and polished them to a mirror finish. Same goes for the carriers to paying special attention the where the ears of the pads sit.

Without removing shed loads of material (and make the pads rattle) I've tickled the surfaces with emery or worst cases and gentle waft of the dremel on the carrier faces where the ears go. Applied a smidgen of copper grease too

[Smeeagain]

[quote="Smeeagain"]
So two questions

What can cause the pistons to stick?
You mentioned the discs warping as it heats up - is it possible that if I fix the sticking piston that the disc will then be fine (I appreciate you havent see the discs and they maybe be fubar but just asking if it is possible that they might be ok after sorting the piston?

R
[/quote]

So back to my second question above, ......

[X5Sport]

It depends upon how corroded the piston itself is along with the slider pins.  If they clean up OK then the caliper is recoverable, but if badly corroded/pitted then throw it away and start with a new caliper assembly.

[Smeeagain]

I was asking about the disc ......

Smee

[Raj]

Once a disc has warped that's it. No going back unless you have it skimmed somewhere to remove the runout.

[Smeeagain]

so why does it only wobble when it is hot and not when it is cold ?

[X5-D-Sport]

SIMPLES my friend, it wobbles when hot, because the calliper piston is partially jammed in its' bore, or the pads are partially jammed in the location slots with lining dust & road grunge baked hard.

The short or slow journey wont heat the disk up & hence all feels fine..

The long and/or fast journey causes the pads/disks to get hotter & hotter due to the pad interference with the disk.... at some point there is a temperature runaway where the pads/piston or calliper expands & the binding increases making the issue exponentially worse rapidly.
The disk will temporarily gently warp over time due to binding & heat & the tiniest warp will then amplify due to binding also.
The disk clearance is a measurement normally measured in "Microns" whereby the pad floats on a very layer of air between the disk & pad... but for all intensive purposes, it is in contact always..
Hence the smallest amount of binding or disk warpage has an effect.
A warped disk may only be 0.05 mm out of true to cause a judder thru the steering...

Simply, order the new piston set, mentioned before, fit it & clear the edges of the bores that the pistons go into of rust debris etc, clean out the pad slots in the calliper, replace the pads... and all will be fine.
Job done, no more wobble.

We can discuss it here for ever, but you just gotta get these parts & fix it.

[Smeeagain]

Simply, order the new piston set, mentioned before, fit it & clear the edges of the bores that the pistons go into of rust debris etc, clean out the pad slots in the calliper, replace the pads... and all will be fine.
Job done, no more wobble.

We can discuss it here for ever, but you just gotta get these parts & fix it.
[/quote]

That's fine I have the parts and it is being done tomorrow, but last question (promise) - re the above if, the disc is warped then surely I also need to add replace disc to your list of chores above? As it happens I have a spare disc and was goign to do that anyway but curious as it wasnt listed
Smee

[M40CCA]

I've had pagid discs fitted 250 miles ago and I've now got a wobble under braking knew I should have bought some decent ones!!!
Can I send these back under any sort of warranty/guarantee ??


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