Help brake judder
 

Advice needed. Can't seem to get rid of my cars brake judder I've tried everything at this stage. Just had discs skimmed and new pads fitted but I've got the same judder leading me to believe it's something other than the brakes any ideas much appreciated .

Where do you get the judder from?does the steering shake as you brake at speeds?do you have bbk or standard discs?standard pipes or braided?
You may need to check your front calipers.check the rubber bellows that cover the Pistons if one even has a slight tear in it it will ingress water that will erode the piston.what might be happening is the piston is seizing and not retracting causing disc to over heat and distort.another thing could be a collapsed brake pipe.best way to check all or any off those is get the brakes hot hot and when you come to lights you need to see if the car will free roll.as in slow down to a crawl and see if it stops abruptly or slows without any help.also even if you've had the discs skimmed and there is debris between the disc and hub you will create the same problem
Ideally you need to do a run out test on the discs and the hubs.
I had an e90 on Friday with a bent hub causing it to push the caliper out.cant explain how it did bend but I could physically see it wobble.

Another idea.do you feel the rear of the car judder when you hit the brakes
Silly question have you checked for a bulge in your tyre or an egg shaped tyre these also are factors

I have Ap bbk fitted front and rear. The shudder is from the front and shakes the steering it's not as bad when I brake lightly but is really bad when I brake harder basically it's taking the enjoyment out of driving the car. I had the calipers off the car and checked them over . All the pistons seem to be moving freely. The wheels where all refurbished recently so I can rule out any buckles in the wheels. The last pads I had fitted Aps own were so dusty the inside pads actually we're jamming in the calipers I thought that might be the cause so binned those pads and fitted new ones skimmed the discs but to no avail I've still got the same problem.

If I'm not wrong those calipers are held by standard bolts but they have washers between the caliper and hub.have you dropped a washer?question2 is is is shit I've lost myself
Oh yeah have you got floating discs or solid?the best way today diagnose this issue is by using a run out gauge question 3 does it vibrate from cold to hot or from hot only? .unless you have a set of discs sitting spare?this all has a bearing on what may be the cause of your issue
You say the piston seem to move freely you need to extend all 6 pistons and check for ANY kind of wear or water damage anything that will cause them not to return.theres lots to it to be honest not easy to diag on the forum.im just trying to guide you through tell tail signs.you need to know if your getting binding from the calipers when hot.where the discs the same immediately after having them skimmed or did it develop again after?when they were skimmed where they done on the car or on a lathe in a workshop?that also has an impact.do I have a spare set of discs you can try?ill have a look.im scared to say it but skimmed discs may not be the cure of your problem.reason being if you took them off got them lathed at a machine shop they may not be 100% and they may not be 100% clean on the mating face of the disc and hub.

Attachment 13135

This how they should be skimmed for 100% alignment to your hub
My own car brand new discs the day after fitting cheap crap spacers

That's the method I used The first time I had them done (pro cut)it didn't cure it completely and it gradually got just as bad again. I've got floating discs fitted. I must check the bolts and washers. Are these the bolts that fit the caliper bracket to the hub?. I only skimmed the discs the second time as I was fitting new pads and with the old pads sticking on the inside it left the discs scored and rusty on the inside.

I've spacers fitted on the front also? Could this be an issue?

Okay make my diag harder for me.
Yes on some ap sets I've seen washers between the caliper bracket and hub mating face.if you don't have washers then you couldn't have dropped one.
Ok so if you skimmed the discs to match the hub it cooouuuuullllldddddd be spacer related.youd need a micrometer to measure all the way round the spacer.
Reason being if one side is 5mm and the other side is 4.8mm when you bolt the wheel down there will be .2mm space between disc and spacer causing it to move which allows it to warp.
Only other thing is to place a run out gauge on your hubs and check run out tolerances.
Are all your wishbone bushes,ball joints rear brake force bushes in good condition?
Only 2 components in my mind can be at fault.1:brake disc bells 2:hubs

What spacers have you got?
Bought my brakes brand new,fitted them run them in.day later I got vibration.spoke to the Americans who insisted I post the discs back to them.it was cheaper to sim them.while I got them skimmed I asked the tech to figure out how they got destroyed.he checked my hub run out,fine.
Checked inside my rims,fine.
Checked my 5mm spacers and found one side was actually 4.8mm cold pressed spacers were my culprit.i waited and bought lazer machines spacers.fitted them and I've had no problems in over 7 years and I e done 10 trackdays.
So I wouldn't rule out a tolerance issue either between hub n bell or bell and rim.