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Break disks, maybe time for replacements?

Posted: Mon Feb 28, 2005 4:58 pm
by Big Brother
While I was checking out the breaks today because I can hear them grinding and squeaking occasionally I found the disks were quite badly rusted around the edges and I don’t know if the lines I can see on them are cracks or just bad stains as it won’t wipe away. Going to have them looked at properly tomorrow.

Image

Posted: Mon Feb 28, 2005 5:11 pm
by dragon
I'd say they are OK at the moment - yes the edges are rusted, possibly very rusted, but they aren't the braking surface, so it's OK. Run your finger from the braking surface up to the edge of the disk, how much of a "lip" can you feel? If it's a couple of mm, they'll probably be fine for another few hundred miles, but if there's a serious lip to them, then yes it's probably replacement time. And what better time to start playing with mechanics yourself, as replacing discs and pads is fairly straightforward - was the first "proper" job I did on my turbo myself :)

As for the diagonal lines - I don't think it's to worry about, the discs that came off the turbo had them, and the discs that went on as new also had something similar. Watch someone tell me I'm wrong and find out I've been driving a deathtrap before it went to DBSs home for upgrades!!! :lol:

Posted: Mon Feb 28, 2005 5:15 pm
by Big Brother
I did run my finger along it but I couldn’t feel anything, I could only feel a slight lip when I ran my finger nail across it so I guess that means they are ok, I was planning to change the disks and pads at some point and anyway and yes I am going to do them myself :) I have the Haynes book of lies to guide me and my dad can make sure I’m doing it right.

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Posted: Mon Feb 28, 2005 5:57 pm
by chris1roll
Those lines are where someone, at some point has caned the brakes from high speed to a complete stop, rather than easing off towards the end of braking. The pads then partly fuse to the disc, leaving those marks. This contributes to pedal judder. I found this from the net somehwere, i'll try and find the link later.

Posted: Mon Feb 28, 2005 5:58 pm
by dragon
Since you said that, it makes sense, and after looking at the pics again, there are 2 oppsite lines, making the rough outline of the pad! :D

Also, caning of brakes generates lots more heat in the disc, which could well explain the advanced flakiness on the rim compared to the apparent lack of wear on the braking surface.

Certainly wasn't me doing that heavy braking, btw: I reserve that for turbo cars when racing certain automatics!!! :rofl:

Posted: Mon Feb 28, 2005 6:22 pm
by martinholmesuk
:rofl:

:lol:

Not the same day the brakes started to smoke :rofl:

:oops:

Posted: Mon Feb 28, 2005 7:13 pm
by Big Brother
I see what you mean Chris. I will be replacing them sometime in the future but the shocks need doing now and these have a couple of hundred miles left in them.

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Posted: Mon Feb 28, 2005 8:20 pm
by dragon
Something's been bugging me since I posted on this topic last - chris indicated the marks are caused by someone stamping on the brakes all the way to a stand before letting the pads off the discs.

But the car has ABS, I would have thought the action of the ABS would allow for enough cooling as it rapidly releases/applies the pads under extreme braking?

Posted: Mon Feb 28, 2005 9:29 pm
by pol
Still going to get hot under harsh braking.. Yep, those marks do look like the outline of a pad, but cant say i've ever seen it before...

pol

Posted: Mon Feb 28, 2005 10:20 pm
by rpruen
It's because they are also the handbrake.

The rear pads also operate when you put the handbrake on, so if the brakes are hot when it is applied, then it will leave material from the pads on the disk. There isn't much you can do about that, other than to drive gently for 10 miles after harsh braking, before putting the handbrake on.

Richard

Posted: Mon Feb 28, 2005 10:58 pm
by vins480t
or just leave it in gear and no handbreak at all
or put it stopped at the pavement