Juddering under braking?

[Somnophore]

Hey guys, the missuses Puma 1.7 is juddering under braking, any ideas what might be causing it, had a look at the discs and pads look ok at a glance, no other issues with handling, just under braking.

[maniac0796]

Discs and pads been changed recently, or have the discs been off? If you don't clean the mating face, then the disc doesn't sit even to the flange, which causes brake judder. It's usually caused by misaligned or warped discs.

[wildman0609]

warped discs.

[tog]

Can it also be caused by worn ball joints?

[Mr.Jimbo]

Ball joints would usually manifest a bit of a wobble under acceleration also.

My guess is warped discs, as I seem to have warped the E30's after chucking it round the ring

[jbi]

wildman0609 said:

warped discs.

no such thing

it could be uneven deposits on the disks though

[Big Rod]

Worn suspension bushes,
Worn track rod ends,
Warped/cracked disk(s),
Misalinged disk(s)
Unbalanced wheel(s),
Misaligned front wheel(s).

JM2pW.

[Mars]

jbi said:

wildman0609 said:

warped discs.

no such thing

it could be uneven deposits on the disks though

Yes, this is correct. Pads deposit material onto the disks to promote braking. If the deposits are unevely distributed, you get friction hotspots.

You can sometimes correct it with the following:

1. Rubbing the disks with a certain "sand" paper (I think it's an aluminium grain but can't remember exactly)

2. Replace pads with harder compound - it **can** have the same effect as above.



Neither of these is certain. My auto Legacy suffers with this every 15K miles or so. I have the disks very lightly lathed each time and just accept it that the life of the disks is reduced to ~45K miles (two lathings from new). Not too bad really. Lathing sorts it out **properly**.

Cause of the problem in the first place? I don't really know. Suspect the Legacy disks/pads aren't really up to the job of stopping this weight/speed of car without engine braking. If I could find a slightly harder pad, I would. I also suspect that, as it's an auto, I do occasionally brake for a junction then sit with my foot on the brake pedal for a short time (never for long - I am acutely aware that this might be the cause of the problem). On hot disks this can promote pad deposits in localised areas.

[Defcon5]

Have you driven it or just relaying what the missus is saying? Could it be the ABS playing up and activating under normal braking

[Superhoop]

jbi said:

wildman0609 said:

warped discs.

no such thing

it could be uneven deposits on the disks though

+1 Warped discs (On road cars anyway) is a complete myth

Discs, hubs and basically any rotating component that is mass produced suffers some run-out.

If both the disc and hub have run-out, then the each side of the disc will contact its corresponding brake pad once per rotation - This, over time, wears away the disc surface leading to disc thickness variation at two points of the brake disc.

This means that the piston has to travel slightly further at these points to keep the pad in contact with the disc - Meaning the piston is therefore has to move in and out, which is felt as a judder through the pedal and steering wheel.

The easiest way to check for this is to remove the wheel and caliper, and measure the brake disc thickness at about 20 - 30 points around the disc - The best repair, assumng the discs are still serviceable is to have them skimmed on the car, which will give not only an even thickness of the disc, but should also allow the disc to run true, preventing a reoccurence

[rob1234]

Go out for a proper hoon and get some really good hard braking in, as if you were bedding pads in.

This is what I have to do with my Mintex 1144s every month to 6 weeks of commuting...