Brake shudder only once

[Shaheenis]

Hi there,

When I was driving down the range from Toowoomba on Friday I noticed a very obvious shudder when I touched the brakes and tested a few times. It was felt most noticeably through the pedal. It is the first time I have noticed this and it didn't feel good. I don't remember being hard on the brakes before it happened either, just cruising. Once I returned to the flat it didn't repeat although I was on a freeway so braking was minimal. The car has 130K with original brakes. The rotors visually look in good condition but I have not removed wheels yet to have a better look. Any ideas?

I did do a search and most threads say warped rotors but I wouldn't expect this to develop after normal driving (last spirited drive was on a cruise 6mths ago) and then go away again.

Cheers,

[BillyCorgi]

Any ideas?

NVH issues are a cow of an item to diagnose. As you are willing to canvas ideas, here are some.

Warped Brake Disc
As this is not reoccurring on "the flat" it may be reduced in likelihood.
To diagnose whether the discs are within run-out tolerances, a dial gauge would be required. Mount the gauge of the brake calliper and use some wheel nuts to ensure the disc is clamped up against the hub.

Glazed Brake Pads
Take them out and inspect. Roughen up the friction surface by rubbing them in figure 8's on a concrete driveway, clean and reassemble.
The harshness will always likely to come back again once the friction material re-beds back in.

Caster Angle Critical
The brakes put a force on the wheel that creates a torque about the centre of rotation (as viewed from above).
The torque created from left and right side equalises through the steering and works in the direction of the natural castor torque from the steering geometry.
If the castor angle is not correct then some shimmying may be experienced during braking. Worn suspension bushes may allow the steering geometry to vary under braking.
One would expect that this would also be felt through the steering wheel also?
We have all had the wobbly wheeled trolley at the supermarket?
This is steering specialist territory

Here is the Brake Diagnostic Table from the Gen4 FSM
http://imgur.com/s73KubA

Good luck with your diagnosis.
Keep us posted with your updates.

[Shaheenis]

Thanks Peter some good advice. It didn't feel like a wobbly shopping trolley wheel (although I know exactly what you mean here), it felt more like a rotational shudder which would be more in line with a brake issue.