Help replacing rear brake pads GSX750 2000

I noticed a scraping sound when pushing my 2000 GSX750 out of the barn
on my last few drives. I thought it was my chain against the plastic
guard. Today I realized my rear rotars were looking scraped up and
rough feeling. I popped out the rear brake pads and they are worn to
the metal. Looks like it's been metal on metal stopping me. I'm not
a mechanic, but can usually fix things myself. I've ordered some new
brake pads, and have the service manual. I have a couple of questions
maybe someone can help with:

1) Initially I hear this scraping sound (even without the brakes
being applied - even as I push the bike), but since the pads were worn
out (and were much thinner) I would expect there would be no (or less)
contact with the rotar. Maybe the pistons were pushing out to far and
locked? If that makes any sense.

2) When I removed the pads, it appeared as if they were contacting the
rotar and were therefor hard to remove (scrapping as I pulled them
out). The pistons seem to be extended. I don't see what pushes the
piston open? I understand the brake fluid closes it. I sort of
expeced to see a return spring? I don't seem to be able to push the
pistons open (at least easily) so I am trying to figure out how I'm
going to fit the much thicker new pads in. Is there a simple way to
open the pistons? Or maybe I have to remove the brake fluid?

3) Should I try and sand down my rotar's with sandpaper maybe? Where
they are sort of rough, I'm guessing they will wear down my new pads
pretty quick.

I would appreciate any suggestions/comments.
Thanks,
Dave

On Sat, 22 Sep 2007 15:07:06 -0700, GSXRDave wrote:

> I noticed a scraping sound when pushing my 2000 GSX750 out of the barn
> on my last few drives. I thought it was my chain against the plastic
> guard. Today I realized my rear rotars were looking scraped up and
> rough feeling. I popped out the rear brake pads and they are worn to
> the metal. Looks like it's been metal on metal stopping me. I'm not a
> mechanic, but can usually fix things myself. I've ordered some new
> brake pads, and have the service manual. I have a couple of questions
> maybe someone can help with:
>
> 1) Initially I hear this scraping sound (even without the brakes being
> applied - even as I push the bike), but since the pads were worn out
> (and were much thinner) I would expect there would be no (or less)
> contact with the rotar. Maybe the pistons were pushing out to far and
> locked? If that makes any sense.
>
> 2) When I removed the pads, it appeared as if they were contacting the
> rotar and were therefor hard to remove (scrapping as I pulled them out).
> The pistons seem to be extended. I don't see what pushes the piston
> open? I understand the brake fluid closes it. I sort of expeced to see
> a return spring? I don't seem to be able to push the pistons open (at
> least easily) so I am trying to figure out how I'm going to fit the much
> thicker new pads in. Is there a simple way to open the pistons? Or
> maybe I have to remove the brake fluid?
>
> 3) Should I try and sand down my rotar's with sandpaper maybe? Where
> they are sort of rough, I'm guessing they will wear down my new pads
> pretty quick.
>
> I would appreciate any suggestions/comments. Thanks,
> Dave

First of all, it's a rotor not a rotar.


Secondly, currently your pistons are out, you need to PUSH them back in.
There is no "return" spring of any kind. When you apply your brakes, the
brake fluid is pressurized and that pushes the piston against your pad
which then pushes against your rotor creating friction and hopefully
slowing you down. When you let off the brake, all that happens is that
the pressure is relieved in the brake system and the rotational force of
the rotor against the pad pushes the rotor slightly back until eventually
there is no more friction. This basically keeps the brake pad as tightly
against the rotor as possible at all times without causing friction and
without having any visible gap.

Now I've seen two types of pistons on cars, not sure what types bikes
use. Haven't done my own brakes on a bike yet.

The one type you can simply push back in with a big C-Clamp. Just put the
C-Clamp around the piston and caliper, and then screw it tight and it'll
push in the piston. Make sure you put wooden blocks or something else in
between the C-Clamp and the caliper and piston to avoid scratches /
damage.

The other type of piston is a screw type piston which would need a
special tool that grabs the piston and turns it back into the caliper.
Can be done with a set of pliers too but I would not recommend it as this
can cause damage to the piston. This type you cannot push in with a C-
Clamp.

Like I said, not sure which type bikes use. You'll have to check that.

Next, your rotor is toast. Get rid of it. It'll wreck your new pads in no
time if it was riding metal to metal it's surface is damaged. Not only
that but it may also have been ground below the specified minimum
thickness which also isn't good. All sorts of bad thing could happen to
it under stress in that case.

Get a new rotor. No, you can't sand it down with sandpaper. Special
machinery is used to resurface rotors to ensure that the surfaces are
perfectly flat. But usually, any rotor that's been metal to metal is
toast and no amount of resurfacing is going to save it as it'll likely
end up below the minimum thickness.

--
Stephan
2003 Yamaha R6

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