What causes brake judder?

[greypianosflying]

Got a MK6 Ford Fiesta which judders slightly through the steering wheel when braking. Nothing major, just annoying.

I've checked that both front wheels are true and round by sticking a pencil to a jack stand and rotating the wheels. Hardly any deviation from the tip of wheels, 0.5mm at most. Also did the same with the disks. Everything it round and true. I checked on both sides of each wheel and disk.

No play in any bushes as far as I could tell. I grabbed the various suspension components and gave them a shake, but no movement. Drive shaft has a bit of play if you push it backwards and forwards towards the transmission, but it is the same on both sides.

Any ideas what else it could be? I did notice that the inner side of the disks were worn slightly more than the outer side. Same on both disks.

Don't think it is a tire balance issue - just had new tires put on and it is exactly the same as it was with the old tires. It seems to have a slight judder when moving normally, but gets worse when braking.

Thanks!

[PositronicRay]

Usually discs. Sometimes the inside is worse, you just can't see it with a backing plate in the way. You want it clean and shiny on the whole of the friction surface.

[Warmfuzzies]

Brake pad deposits 9/10 times

K

[BigTom85]

I agree that the most likely cause is brake pad deposits on the discs, or a very slight warp. They are so cheap I'd just replace the pads and discs to be honest.

[TheAllSeeingPie]

BigTom85 said:

I agree that the most likely cause is brake pad deposits on the discs, or a very slight warp. They are so cheap I'd just replace the pads and discs to be honest.

Yup definitely worth swapping them out. In the past I've had it where either the discs are on their way out or the pads have worn funny.

[greypianosflying]

Thanks for the help. Will change the disks / pads if it gets worse.

Car is on 70k with the original disks / pads. Still loads of meat left.

[bearman68]

greypianosflying said:

Got a MK6 Ford Fiesta which judders slightly through the steering wheel when braking. Nothing major, just annoying.

I've checked that both front wheels are true and round by sticking a pencil to a jack stand and rotating the wheels. Hardly any deviation from the tip of wheels, 0.5mm at most. Also did the same with the disks. Everything it round and true. I checked on both sides of each wheel and disk.

Thanks!

0.5mm on the disk is HUGE.
Should be about 0.07mm, so tight you need a DTI to measure it.

Normally caused by differences in friction on the disc though - the above tends to cause excessive movement in the brake pedal.

[Boosted LS1]

Parkinsons, I'll get my coat.

[CarsOrBikes]

A pencil inside the wheel isn't going to tell you, if you had a dti gauge on the disc both sides it would, and a micrometer which will tell you the disc thickness variation, but as others say, economical parts, and at 70k OE they're done. If you have a judder that is only initial that settles, it may be more likely a soft or worn control arm bush. I'd just swap the brakes at 70k anyway.

Only my2p