re: GTV-6 quirk #2 (noise)

[TJCallahan@domain.elided]

In AD v8n636, Joe wrote about quirk 2, an intermittent, quiet "whum" noise 
from the front left.

Joe - My money says it's the brake pads rubbing on the rotor as the 
wheel/brake assembly turns. The condition is caused by too much runout - you 
have a rotor that's not quite true. Disk brake pads are designed to stay 
waaay close (technical term) to the rotor. 

When there's too much runout (rotor true), as the wheel/rotor slowly rotates, 
the pad comes in contact with the rotor and you get the 'whum' sound. Then, 
as the rotor turns more and the contact between the pad and rotor is broken, 
the 'whum' sound ends. Based on your description ('... when inching forward 
it sounds like "whummmmm...whummmmm" ...'), you're getting a single long 
'whum' per turn of the rotor, so the frequency of the 'whum' increases as the 
wheel/rotor turns faster ('... at, say, 20 mph it sounds like "whumwhumwhum"' 
...).

If the rotor is true, you get no contact between the two surfaces until you 
step on the brake pedal and, by then, your passenger is screaming so loud 
that you can't hear the 'whum' sound anyway.

When you're at speed and you step on the brakes moderately hard, does the 
front end shimmy through the steering wheel? Even a little? If it does, 
that's another sign you have a rotor out of true.

Let's see, fixes could include:

1. replacement of the pads and rotors
2. checking the tightness of the lug nuts (if they're too tight, it can 
affect the hub, rotor, and wheels)
3. ensuring the rotor is seated properly on the hub (these are 'top-hat' 
rotors, right?)
4. ensuring the front wheel bearings are in good working order and tightened 
to spec

YMMV

Tom
Seattle
10123 (no rotors, beautiful Alfin triple shoe drums)
11615 (who needs brakes?)

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