Re: Disc Brakes

[patmor@utu.fi (Patrick Joel Morton)]

At 14:24 8.8.1997, Adriaan Loedolff wrote:

 * This happens because the disc pad does not contact the full width of
 * the rotor. A slight ridge then developes over a period of time untill
 * the pad actually runs in a wide groove in the rotor surface.

My brakes squeaked horribly after just 3,000km and I had new rotors, pads
and discs.  I thought it was the bearings - which were also new, but it
wasn't.  In the morning when the brakes were cold, the sound was
unbearable.  I drove about 200m in a straight line with the brakes and gas
on until the noise ceased.  I am glad that I have a new clutch as well.

 * This groove could be as shallow as a few thousands of an inch!

Well, I put my rotors onto a lathe and checked them for variations in
thickness.  There was no groving at all.  That theory went out the window.
I did polish them at the same time.  I also re-greased the bearings and
cleaned the rotors.

 * The squaling sound occurs when the edges of the pad cathes the edge
 * of this ridge cousing them to vibrate - even with the Brake-Quiet
 * stuff behind the pad. Incedently, one should'nt have to use any
 * vibration dampening compound on VW disc brakes. Behind the pads are
 * little piston retaining plates that hold the pistons at a 20 degree
 * angle thus preventing them from rotating and causing the brakes to
 * squeal.

This is true.  I am pretty sure that the sound comes from the pads (did not
take a rocket scientist to figure out that one).

[snip]

 * If you ever need new discs for a pre '71 type 3 and cannot find them
 * you could use discs off a later type 3 or a VW 411 or 412. They
 * all use the same wheel bearing and the discs are are thicker
 * so you car machine them down to the correct spec. for your vehicle.

I have never heard of this before - probably because I have never found a
set of TIV discs.  Actually, a customer has been looking for a pair for six
months now ... Big Boys had one disc in stock!  But who is interested in
Type IV heaps anyway!

BTW, Type III discs are readily available from many places.

Anyway, on Tuesday, I changed the pads.  The old ones were slightly worn
(probably from me driving with both the gas and brakes on), but otherwise
just fine.  I actually sold the pads later in the afternoon with my old
rotors!  Thankfully, now the noise is gone.  But lets see what happens
after another 3K.

Stay tuned.

Patrick