Minimum Brake Rotor Thickness

VA_Alfa · #1 (**permalink**) 04-20-2009, 04:57 AM

I'm getting ready to replace brake pads on my 69 SV and I have a few questions from the more seasoned ATE brake people before I get started.

1. Is it standard practice to turn the rotors down at a brake pad replacement or is a complete disc replacement in my future?

2. What is the minimum brake disc thickness specification for a 69 SV?

Thanks

**TorW** · #2 (**permalink**) 04-20-2009, 05:32 AM

1. Can't tell you what the standard practice is (not a shop, owns only one 105), but if the discs are straight and true (i.e. run-out within specs), I wouldn't turn them down.

2. 8.5 mm (.394") rear, 10 mm (.335") front, according to the DIASS manual

VA_Alfa · #3 (**permalink**) 04-20-2009, 04:45 PM

Dumb question: What is the DIASS manual?

**papajam** · #4 (**permalink**) 04-20-2009, 06:40 PM

DIASS is short for DIrezione ASSistenza Technica, the department within Alfa Romeo that, among other things, publishes technical, service and owners manuals.

**aralfa8589** · #5 (**permalink**) 04-20-2009, 07:17 PM

There may be other opinions, but it isn't always necessary to turn rotors at every pad replacement. There are symptoms that indicate turning rotors is needed...oscillation under moderate/heavy braking for example. Turning usually takes off about .015/side, so you can measure the initial width and figure if there is enough meat to end up with the minimum acceptable rotor thickness. I don't do it just as a matter of course...It is good to knock the glaze off of the rotors if you don't turn them.

Jim will reply, and you can take whatever he says to the bank!

VA_Alfa · #6 (**permalink**) 04-20-2009, 08:24 PM

With the front end on jack stands and the wheels off, I checked the rotors this evening. They show very little wear, no scoring, no pitting, etc. Is there a shadetree mechanic method for knocking the glaze off the rotors without removing them from the vehicle?

**TorW** · #7 (**permalink**) 04-21-2009, 03:50 AM

I used 600 grit sanding paper on my front rotors to remove glazing. Just wrap the paper around a piece of flat wood and apply it lightly to the rotor while you turn it.

barbone105 · #8 (**permalink**) 04-30-2009, 04:52 PM

there should not be any glaze.... if so, might want to look at a better pad.
in any case, coarse sand paper should do the job.
andy

**papajam** · #9 (**permalink**) 04-30-2009, 05:26 PM

Oh, poo. I forgot to post to this thread.

While sandpaper is commonly used to remove glaze, industry standard practice is to have a non-directional finish on the surface. This means making swirls on the surface of the rotor (caliper removal required for the inside surface). A non-direction finish reduces the pads' tendency to vibrate (squeal).

**aralfa8589** · #10 (**permalink**) 04-30-2009, 06:15 PM

All rotors will be glazed-shiney, I use 120 grit and seat the pads hard...

**Tifosi** · #11 (**permalink**) 04-30-2009, 06:59 PM

Quote:

Originally Posted by papajam

This means making swirls on the surface of the rotor .....A non-direction finish reduces the pads' tendency to vibrate