Is250 Brake Disc Thickness

[Lexus-IS]

The official lexus tech doc says that the standard thickness of the front discs are 28.00mm and the minimum thickness is 25.00mm. It says to use a micrometer to measure the thickness from the back surface to the front surface and if below minimum thickness then replace the disc.

Does this sound right? Thats basically a wear of only 3mm allowed on brand new discs? if that's the case how long can discs last?

Most mircometers on eBay seem to only go from 0-25. anyone know where i can get one that goes to at least 28mm ?

Also, the front pad minimum thickness says 1.00mm and it says to measure the pad lining using a ruler. Can anyone explain where i start the measurement from?

Thanks

[johnatg]

Those dimensions are correct. Discs don't wear much and they are more likely to be well grooved and generally not in great nick before they measure less than 25mm. They usually last over a couple of pad sets. Once upon a time they lasted more or less the lifetime of the car, but banning asbestos has meant that pads are much more abrasive now.

You can get bigger mikes on eBay or from places like Machine Mart. But don't bother - buy a dial caliper instead. Hold a couple of nuts against the discs and measure the combined thickness with it, then deduct the combined thickness of the nuts. That avoids measuring the edge crud. Dial calipers measure to 0.1mm - all you need.

You can get digital ones but they need batteries and if you don't use it much they'll be flat whenever you do want to use it. Mechanical ones are fine.

Measure pads from friction face to the start of the backing plate - ie just the 'lining', as we used to call it!

[Lexus-IS]

Would this do the trick: http://www.ebay.co.uk/itm/121434135675

Only problem i see with it is that the ends are flat so it wont go and touch the surface of the disc itself. Like you say maybe I can put a nut/washer or something on each end and minus the thickness of that.

[johnatg]

Yes - but it needs batteries, and they'll be forever flat. I find one like this much better:

http://www.ebay.co.uk/itm/PROOPS-METRIC-DIAL-CALIPER-VERNIER-MICROMETER-150mm-15CM-STAINLESS-HARDENED-/351211489820?pt=UK_Measuring_Tools_Levels&hash=item51c5d60a1c

And yes - you just need a couple of small hard flat things either side of the disc.

OK a micrometer would do the job in one go, but you'll probably only use it once in a blue moon, especially a 25-50mm one. Dial calipers are quite useful for quite a range of things. (eg you can use the depth function for measuring the brake pads!)