Brake Disc Thickness and Pad Wear

[james250]

It seems the the thickness of brake discs from new to to minimum value has only a tollerance of 2mm. So whatever the thickness of the brake disc is brand new, the minimum thickness before it needs changing is 2mm minus that. So in case of the IS250 the front discs are 28mm new and minimum thickness is 26mm. Other cars also seem to have the same 2mm wear threshold. Is this correct? Is 2mm the maximum a brake disc can wear out?

Also, how can you visually tell when brake pads are nearing the end? I've attached a photo below of a brand new brake pad and illustrated on one with a red mark, when that groove slot runs out is that the end of the brake pad life?

[jumbojake]

I've always taken the minimum thickness to mean just that, the minimum thickness of friction material left on the pad... to be honest I changed them before then, as the wear indicator scraper makes one hell of a noise at about 5mm.  I check them twice a year when I swap winter/summer tyres and check the calipers.  5min job when the caliper is already off.

Where did you read new - 2mm ? ... seems like a wasteful approach.

[james250]

56 minutes ago, jumbojake said:

I've always taken the minimum thickness to mean just that, the minimum thickness of friction material left on the pad... to be honest I changed them before then, as the wear indicator scraper makes one hell of a noise at about 5mm.  I check them twice a year when I swap winter/summer tyres and check the calipers.  5min job when the caliper is already off.

Where did you read new - 2mm ? ... seems like a wasteful approach.

ECP brake disc specs for front say new 28mm and minimum thickness is 26mm. But the Lexus tech doc says minimum is 25mm

[jumbojake]

ahh ... your talking about the disc itself  (not the pads)... yes,  that is more sensitive to wear .  Best to always check the Lexus requirements, not rely on shops.

for the front, Lexus state 28mm new, and 25mm minimum  (3mm wear) ... to gauge that use a micrometer or vernier.   I've just change my front, about 60000miles, seems reasonable.

[johnatg]

Yep - min front brake disc thickness is 25mm in workshop manual- not sure what is etched into the rim of the disc but the minimum is always specced there as well.

My car has solid rear discs - original thickness is 8mm, minimum 6.5mm.

According to Lexus minimum pad thickness is 1mm, but the MoT spec is 2mm and you will get an Mot fail for less than 2mm.

2mm is somewaht lower than where the slot ends, so the slot can (usually) be completely gone before the pads are illegal

[Britprius]

Strange thing is with the MOT the discs can be below minimum thickness without triggering a fail as long as they are not cracked or broken. 

The choice of brake pad material has a significant bearing on the ware rate of the discs. This is something often not taken into consideration when choosing new pads. I have seen pads with so much metal content that the discs need replacing before the pads.

John.

[rayaans]

On 7/7/2019 at 1:01 PM, Britprius said:

Strange thing is with the MOT the discs can be below minimum thickness without triggering a fail as long as they are not cracked or broken. 

The choice of brake pad material has a significant bearing on the ware rate of the discs. This is something often not taken into consideration when choosing new pads. I have seen pads with so much metal content that the discs need replacing before the pads.

John.

True, thus why Ive always been told to match brake discs and pads from the same manufacturer

[Linas.P]

On IS250 Discs wear is horrible anyway, no matter what pads you use. OE discs barely last 2 sets of pads, any softer pads would result in much more brake dust and Lexus low dust pads (although more aggressive) doesn't really wear discs much more, still requires replacement every second time.

[Bluejohn]

Hey.  I saw a thread that mentioned L1NAS.  I have a car that would work on.  Do you know where it is ? 

[Linas.P]

Not sure why this appears as sticky note on my profile and a bit confused how it is relevant to the thread:

Anyhow, I never seen L1NAS (number plate) for sale. However, I have accidentally noticed that such plate exist and it is attached to the exactly same car as mine Black Lexus IS250 SE-L. As it would be perfect match for my name I though that it is strange coincidence it is as well attached to the same car - perhaps another Linas has black IS250. In other hand I am not sure I would like to drive car with my name on it... sound like good idea at first, but when you think about it more it would be kind of weird.