STi Brembos - Manufacturer's Minimum Recommended Thickness

[LaszloT]

Most leading vehicle manufacturers recommend brake disc skimming (US: rotor turning) as a solution for lateral run-out (warping), vibration issues and brake noises. The machining process is performed in a brake lathe, which removes a very thin layer off the disc surface to clean off minor damage and restore uniform thickness. Machining the disc as necessary will maximise the mileage out of the current discs on the vehicle.

However, replacing your brake pads yourself can save you a lot of money with repair facilities charging upwards of $150 for the service, as of 2010. Repair facilities commonly use the fact they turn your rotors to account for the high charge. Many times you do not need rotor turning which can cause problems such as warping, excessive run out and brake noise. Brake rotors only need turning when you find large grooves in the rotor or heavy shaking when braking.

What are the risks of replacing the pads without first turning the discs, if it's Subaru's standard practice to do so?

[nitrowsb]

There are no risks unless there excessive run-out but in most cases it's the differences in thickness that causes brake pulsation.
If there were no problems with noise or pulsation before pad replacement then it's safe to assume that there will be none after new pad replacement.
Some manufacturers don't even recommend machining unless there is pulsation!

But if you really want rotors machined...I can do it for you(off vehicle only) for next to nothing!

[STeveD]

28mm was the minimum thickness for the 2004 STi yes. (30mm starting thickness) If those are your rotors, you're going to find that shops don't like skimming cross drilled or slotted rotors because it breaks the lathe blades. You can get it done, but only maybe 20% of shops will do it for slotted/cross drilled.

The risk in not skimming is that there is a transfer layer on the old rotor that the new pads won't like. For example, EBC Reds HATE Ferodo DS3000 transfer layers... they won't bite at all until you get rid of it. So what I do is remove the old rotor and use 120 grit sandpaper in a circular motion to remove most of the old layer (usually you can't see it) and scuff the surface enough for the new pads to bite. You don't have to scratch it deeply! Swirl marks are what you're going for, not scratch marks.

Or, if the surface is very uneven, you won't get a full contact patch initially.

When you get to be a hardcore Solosprinter / Track guy, you'll buy a separate set of front pads and rotors that you can swap when you arrive at the track.

[STeveD]

Geoff is selling a set of rotors that would fit your car. He comes to Toronto area now and again.

http://www.ottawasubaru.com/forum/viewtopic.php?t=25309&highlight=

[LaszloT]

Smiley,
I may take you up on that, but first will check to see if there are any grooves in the rear rotors at all.

Steve,
I'm planning to replace the OEM set of rear pads with Ferado DS2500 pads. Do I need to scuff the surface of the rear discs for this swap?

[STeveD]

No, I don't think that you will need to. Rear brakes don't do much, and the compound on the OE pads is similar in nature to the DS2500. Most likely, these would just be installed with no other effort. Look for deep grooves, but otherwise you should be good.

Minimum rear rotor thickness is 18mm and they wear very slowly if you never machine them.

[LaszloT]

Surface of the rear discs is very flat without noticeable grooves at all. There is a tiny ridge at the top and bottom of where the pad runs, which I estimate to be 30 thousanths of an inch.

I'm going to change them myself, and I found this how to link, entitled 2008 Subaru Impreza WRX STi : Brake Pad Change :

http://blogs.insideline.com/roadtests/2009/01/2008-subaru-impreza-wrx-sti-brake-pad-change.html

[LaszloT]

Rear brake pad change complete, with Ferado DS2500's all the way around now.

The rear pads had about one (1) mm of friction material left - which was close - and the Ferodo pads don't have the Brembo pad's wear indicator tang on them.

That was fairly straight forward job.

[JoeT]

Isn't it amazing how simple the tasks really are? (even for an engineer) ;-) LOL

Seriously, brakes are so simple, specially the brembo's that it's almost highway robbery to take it to a shop to do. Rotor replacement is simple too.

[Cavemanrjc]

Only easy when not rotten,
Mazda uses a similar system with the pins holding the pads. they get so rusted together that its a major task to do even just a pad swap,

I hate salt :)

[LaszloT]

Caveman :
Automated car washes with undercarriage spray are the ticket to preventing rust. This is the single best thing about a car wash that is often overlooked.
Canadian Tire gas bars often have car washes...
And they're 5 cents per litre off of fuel now, if you get the best one - plug, plug, lol.

[Cavemanrjc]

yes and you and I know that, but the vast majority of owners don't really care as much as you would think,
turn key and go, and if it fails, take it to the shop.

as a tech i get to see all the great wondrous designs and what neglect causes to them.

my stuff comes apart easy, only due to the amount of times i have to replace broken bits :)

race it,break it, fix it, repeat :)

I had a good year, only blew up 1 Honda, not a big loss :)